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Unread 03-31-2007, 01:47 AM   #1
dragginwagon406
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1998 TJ Wrangler 
 
Join Date: Jul 2006
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Cooling System knowledge - Coolant Antifreeze Overheating Thermostat Troubleshooting

I happened across a great article by Steve Litt on cooling systems the other day and saved the link. This seems to be a well researched and written page and should help sort just about any cooling system woe. Sorry for pasting a book, but it is great information which many of us should apply.

http://www.troubleshooters.com/tprom...204/200204.htm

For those who will look at this later and see the link broken:

How Cooling Systems Work
By Steve Litt

The cooling system has one and only one purpose -- to remove excess heat from your engine. As your engine burns gasoline, a little less than a third of the released energy goes into mechanical energy to run your car. The rest is converted to heat. Some of that heat is blown straight out the tailpipe, while the rest heats the engine itself. Without a cooling system, the engine would be destroyed by heat within 3 to 30 minutes of startup.

The cooling system works by moving coolant (water plus antifreeze) through the engine, and moving that heated coolant through the radiator, where its heat is transferred to the surrounding air. The cooling system must have enough cooling capacity to cool a car ascending a long, steep mountain road, where the driver might have the gas pedal 2/3 of the way to the floor.

But it must be regulated in such a way that at a steady 40 MPH on a flat road in subzero weather, the engine's temperature is allowed to quickly rise to the manufacturer's recommended temperature (usually about 200 Farenheit, give or take 20 degrees). That recommended temperature should also be maintained when the car goes up a 10 mile 7% grade in 100 degree weather. Such regulation is accomplished by the car's thermostat -- a heat sensitive valve that allows coolant to flow through the radiator at high temperatures, but cuts off that flow at low temperatures.

The water pump sucks cooled coolant from the radiator and pushes it into the engine. The coolant flows through the engine, absorbing the engine's heat. If the thermostat is open, that coolant then flows into the radiator for cooling. As it flows through the radiator, it heats the tubes and fins on the radiator, and that heat is transferred to the air flowing through the radiator. At low speeds that air flow is maintained by the fan, and at high speeds it's maintained by the relative velocity of the vehicle in relation to the outside air.

Meanwhile, a parallel path brings hot coolant from the engine through the heater in the passenger compartment, and back into the water pump. That path is controlled by the heater valve, which in turn is controled by the lever or electronic climate control on the dashboard. The parallel path is not restricted by the thermostat, so passengers get heat even when the thermostat is closed. However, some cars have a mechanism which shuts off coolant through the heater during an overheat, I guess on the theory that you want to maximize flow through the radiator by shutting off the heater. While such a theory might be credible when the cause of overheating is low coolant, it prevents the alert driver from turning on the heater full blast and thereby letting the heater act as a second radiator. Perhaps such a shutoff is a safety feature so there's no way overly pressurized coolant can rupture the heater and spray on the passengers. So if you've had symptom where "the car overheats and then the heater blows cold air", the heater probably has been shut off due to overheat.

The entire system is sealed with one exception. The radiator cap contains a spring which maintains a constant pressure by venting coolant (to the reservoir tank) when pressure rises above its specified value -- typically around 15 PSI. It's normal for some coolant to vent in this way, which is why the reservoir is more full when the car is hot than when it's cold. The radiator cap also allows the vacuum created when the system cools to "suck back" coolant from the reservoir. But in the case of an extreme overheat, vented coolant overflows the reservoir, thereby creating a low-coolant situation and making the overheat even worse.

Looking at the diagram, you see that oil, gasoline, combustion gasses and coolant all flow inside the engine. These materials are kept separate by the head gasket(s). A breached or broken head gasket, or a bent head, allows any or several of these materials to mix. Coolant into the cylinders produces huge clouds of white exhaust (steam) out the tailpipe. Coolant into the oil produces a yellow/white foam or gunk on the oil cap, as well as degrading the oil, possibly past the point of lubricating usefulness. Combustion gasses leaking from the cylinder to the coolant might produce no obvious symptom, but it's an extremely dangerous condition, because it can cause an overheat by any one or more of four different mechanisms:

1. By forcing excessive coolant out the reservoir, thereby creating a low-coolant situation
2. By forming a gas bubble around the thermostat's sensor, thereby preventing the thermostat from opening
3. By heating the coolant to such a degree that the radiator cannot dispense all the heat
4. By breaking down the coolant's corrosion protection, thereby damaging the water pump or radiator, ultimately causing overheating
It's possible for a broken head gasket to allow combustion gasses into the coolant, without allowing coolant into the cylinders or coolant into the oil or oil into the coolant. In such a situation, the broken head gasket could silently cause overheats. The definitive test for this type of head gasket problem is to test for combustion gasses at both the radiator fill pipe and at the reservoir.

Excess Cooling Capacity
Automotive cooling systems must have HUGE levels of excess cooling capacity. Next time you drive 60 mph on a flat deserted road, notice how far you push on the gas pedal. Probably a millimeter to a centimeter. Now see how much you need to push the gas pedal to ascend a 6% grade at 45mph. Probably an inch or two. Go up to 65 and on some cars you'll be near flooring it. 1/3 of all that gasoline is consumed heating the engine.

Your cooling system must be able to get rid of all that heat. Difficult enough, it becomes even more of a challenge if the air temperature is warm (less heat transfer from radiator to air), and brutal if your car is heavily loaded or towing something. If the heat generated by combustion significantly exceeds the cooling capacity, you'll severely overheat quickly (typically after a mile or two of climbing).
A well functioning cooling system has the capacity to maintain the engine at under 100 degrees temperature during continuous 50mph level drives on cool days. But of course the temperature needs to be 160-230 Fahrenheit, depending on the car (consult your owners manual). That means in most driving situations the cooling capacity must be partially defeated. This is accomplished by the thermostat, which acts as a deliberate bottleneck, regulating the amount of cooling to keep the temperature at a proper level. A somewhat typical thermostat would be closed until 180 Fahrenheit, after which it would open further as the temperature increases, until at 195 it's completely open. This means that in the 15 degrees between 180 and 195, the cooling capacity would go from 0 to the full capacity of the system (enough to scoot up a long 6% grade at 65 mph carrying 5 people in a well designed and maintained machine). Below is a graph showing how temperature increases with increased engine heat production (i.e., more gas):

The portion in blue represents a level of heat production so small that it can be disbursed by the direct contact of the engine with ambient air. In practice this might be achieved in the case of a 40mph wind blowing into the open hood of a car idling in the deep of a northern Minnesota winter's night, but otherwise this condition is never seen in real life. An idling engine, and certainly driving, at anything resembling normal conditions requires radiator cooling.

NOTE: Don't make the mistake of thinking the preceding diagram represents temperature versus time. While that graph would look similar at the leftmost part of the graph, that's not what's being represented. You can think of the preceding diagram as a graph of various driving conditions, each maintained for 10 minutes or more.
The violet portion represents heat production levels within the regulated cooling capacity of the cooling system. The slight temperature gain across this range is due to the fact that the thermostat opens slowly and steadily over a range of about 15 degrees Fahrenheit. This is the normal operating range of the vehicle. Once the engine is warmed up, all driving should be done in this range.

The red portion represents a heat production level beyond the cooling capacity of the cooling system. The temperature goes sky high. On a well maintained vehicle, you would expect the red portion only when the car is used beyond its design capabilities, like using a compact car to pull a trailer up a long 6% grade.
The bottom line is that on a well maintained vehicle, the bottleneck, by a huge margin, is the thermostat. Contrast that with a vehicle with a compromised cooling system not capable of cooling a hard worked engine, or in extreme cases even a lightly worked engine:

Here there's no regulation. The entire graph is basically a straight line. Moderate hard usage sends the car into the red. The operating temperature of a vehicle in this state of repair would vary widely with ambient temperature and length of time driving. Typically no "normal operating temperature" can be identified for a vehicle in this condition. Such a vehicle will almost certainly experience a catastrophic overheat the first time the driver takes a lengthy drive, or drives in hot weather, or drives up a moderate hill.

The controlling bottleneck of this vehicle is not the thermostat -- it's something else in the cooling system. The automotive technician's task is to find that bottleneck.
Steve Litt is the author of "Troubleshooting Techniques of the Successful Technologist". Steve can be reached at Steve Litt's email address.


Last edited by dragginwagon406; 03-31-2007 at 02:55 AM..
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Unread 03-31-2007, 01:48 AM   #2
dragginwagon406
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Cost of an Overheat
By Steve Litt

This article is written primarily for the car owner. Professional Auto Techs know this information all too well, and most do it yourself mechanics know it also. Anyone not knowing this information leaves himself vulnerable to making some very bad decisions that will cost a great deal of time and money.

Sometimes you get lucky and an overheat can be corrected by fixing its root cause. But all to often, overheating -- even a single 3 minute incident -- can cause consequential damage that costs thousands to fix. An overheat is a very bad thing.

The most common consequential damage is a broken head gasket. This happens when the head and block expand differently than the head gasket, or even worse, when an aluminum head and a cast iron block expand at radically different rates, breaking the head gasket. Bimetal engines, whether they be aluminum heads on a cast iron block, or cast iron heads on an aluminum block, are likely to break head gaskets with the slightest overheat. Unfortunately, replacing head gaskets is a big job requiring hours for even an experienced mechanic with all the right tools. For a do it yourselfer, it could be prohibitively time consuming or even impossible. As a result, the cost of replacing a head gasket ranges from $500.00 to $2500.00, depending on the make and model, and whether the heads must be machined.

Broken head gaskets result from a moderate overheat, or even a mild overheat on a bimetalic engine. A more serious overheat can bend or break the heads. Now you have a large parts cost to add to the huge labor charge for replacing the head gasket(s). New heads cost hundreds, and machining heads is also costly.
Some folks consider continuing to drive the car with a broken head gasket. That's a very bad idea if you want to keep the car more than a year. Combustion gas in the coolant can easily cause even more severe overheats, plus it can quickly cancel the anti-corrosion properties of your antifreeze, leaving you open to corrosion, leaks, and blockages, all of which result in further overheating. If coolant gets into the oil, the oil's lubricating ability is compromised, leading to engine seizes, bearing freezes, and all sorts of other problems. If coolant gets into the cylinders it can cause a broken starter, solenoid, or flywheel. Broken head gaskets often make the car run poorly, and often make it a gross polluter, which can be costly indeed in states that enforce smog regulations.

Your engine was designed to operate at a certain temperature. When it operates colder than that, emissions go up, efficiency goes down, and engine wear increases. This is why cars don't drive as well cold as they do when they're "warmed up". On the opposite end, cars operating hotter than designed, even at temperatures lower than what it would take to break a head gasket on a cast iron block/head combination, risk pre-ignition/detonation caused by too-high engine temperature. Such pre-ignition/detonation can damage various components in your engine. If you've ever driven a seriously overheated car you know it sounds much different, and it doesn't sound good.

But what if you're one of these wild and crazy guys who doesn't shut down the car even when the temperature gauge is pinned, there are huge clouds of steam coming out the hood, and the car has started running funny. You, my friend, will most likely need a new engine. Extremely overheated engines seize, freeze, warp, and who knows what else. Engines aren't too expensive, but the labor is prohibitive, and all too often the new engine lasts 10,000 miles and then blows up.

Added to those costs is the cost of having an unreliable vehicle. Cars that overheat once tend to overheat often; unless an unusually competent and comprehensive repair job is done. Overheats results in a tow charges, missed work, and even hazards to personal safety. It's doubtful anyone's personnel record lists "broken head gasket" as a cause for job termination, but it just might list "excessive absence" and "unreliability".

I hope I've gotten your attention. A single overheat can cost you thousands. You need to know that, because during the rest of this magazine I'll be recommending preventive maintenance that costs nearly $100.00 per year, and diagnostic procedures which cost almost $100.00 not counting the actual fix. When evaluating the cost of my suggestions you must realize the cost of the alternatives -- $1500.00 to fix a head gasket, $300.00 for a new radiator installed, and if you go to an incompetant Automotive Technician who practices diagnosis by serial replacement, you'll spend even more.

When viewed alongside the alternatives, $100.00/year to keep your cooling system healthy starts sounding downright cheap.
Steve Litt is the author of Rapid Learning: Secret Weapon of the Successful Technologist. He can be reached at Steve Litt's email address.

Anatomy of an Overheat
By Steve Litt
In the simplest possible terms, any overheat must be caused by one of these five causes:
1. Grossly malfunctioning engine
2. Using the vehicle beyond its capabilities
3. Inadequate cooling system
4. Low coolant level
5. Inability to adequately transfer heat

Grossly malfunctioning engine
This almost never happens. In order to produce enough heat to overload a well functioning cooling system, the car would need to be in such bad shape that going 55 MPH would require pressing half way down on the gas. A car this mistuned would have many more symptoms. Sometimes a grossly mistuned or damaged engine combines with a compromised cooling system to cause an overheat, but it's extremely rare that the primary cause of an overheat is a malfunctioning engine.

NOTE:
Considerable documentation on the web and in other places states that an overly lean fuel mixture can cause overheating, so you might want to check your mixture. That being said, I can tell you that my 1973 Ford Country Squire ran incredibly lean (former owner's smog workaround) and yet did not overheat.

Using the vehicle beyond its capabilities
This is pretty obvious. If you tow a heavy trailer cross country using a little truck with a small six cylinder engine, you're using the vehicle beyond its capabilities and should not be surprised if it overheats. If you expect to do hauling and towing, at the least you need a radiator designed to dissapate the heat generated by an engine hauling a load up a mountain road.

Inadequate cooling system
Many cars are manufactured with cooling systems barely capable of cooling them in extreme conditions. If such a vehicle goes up a 10 mile stretch of 6% grade when it's 100 farenheit outside, it's likely to overheat. If a car with little excess cooling capacity is driven in stop and go traffic on hot days with the air conditioning on full blast, it's likely to overheat. If a relatively new car overheats in challenging conditions but not straight 40 MPH drives on 60 degree days, it just might have been manufactured with insufficient excess cooling capacity.

In addition, many used cars have insufficient cooling capacity because somebody cut corners when replacing a radiator. I once bought a Dodge Coronet with a radiator salvaged from a Dodge Dart. On hot days the slightest hill would overheat it. I had a radiator shop make and install a huge custom 4 row and it no longer overheated. Some used cars lack cooling capacity because the fan shroud has been removed. Such cars tend to overheat more at idle and low speed.
If you've proven to a reasonable degree that the car's cooling system, as manufactured, is insufficient to cool the car during extremely challenging driving, see if you can install a higher capacity radiator. Install the highest capacity radiator you can purchase or have manufactured.

NOTE:
When replacing a radiator, it's best to use a similar type of radiator, but bigger. For instance, if the original radiator was aluminum, it's best to make the new radiator aluminum. Try to replace plastic radiators with bigger plastic radiators. If you need to use a different type replacement, be aware that you might need to change the type of antifreeze you use.

Low coolant level
Low coolant level is a more common overheating cause than grossly malfunctioning engines, usage beyond capabilities, and inadequate cooling systems combined. If coolant gets seriously low, cooling capacity is compromised and the engine overheats, either in challenging circumstances or sometimes in all circumstances.

When researching low coolant it's important to discover where the coolant is going. It's either leaving through the radiator cap or reservoir, or it's not. In either case, there are various mechanisms:
• Coolant leaving SOMEWHERE BESIDES through reservoir or radiator cap
o External leak
o Internal leak
• Coolant leaving through reservoir or radiator cap
o A breached head gasket allowing combustion gas into the coolant, thus pushing the coolant out the reservoir.
o A bad radiator cap allowing coolant out the reservoir (or occasionally right out the cap).
o An existing overheat venting excessive coolant into the reservoir, overflowing the reservoir. Note the coolant could be in vapor form.

External Leak Not Involving the Reservoir or Radiator Cap
A pressure test can prove leakage other than out the reservoir or radiator cap. By replacing the radiator cap with the pressure tester, large pressures can be put into a completely closed cooling system. If the system holds pressure, there's no leak. If it doesn't hold pressure, there's a leak, at which time your job is to find it. If the leak is to the outside of the engine (and most are), you should see coolant dripping. Then you need to follow its trail. If you can't see well enought to follow its trail, you can put ultraviolet sensitive dye into the coolant, hang an ultraviolet lamp (a black light) in the engine compartment, and see the river of luminescent coolant. Typical sites of external leaks are:
• Hoses
• Radiator
• Water pump (especially at the drain hole)
• Freeze plugs
• Heater core (coolant smell inside passenger compartment, possibly puddles on floor of passenger seat)
• Drain plug on engine
• Drain petcock on radiator

Note that in the case of the heater core, a pressure test might not reveal that leak because the heater valve may be shut. Let the engine run til it's hot (but nowhere near overheat), and with all the car doors shut and the windows closed, turn the heater on full blast and carefully sniff around the passenger seat and the floor of the passenger seat (wear eye protection and be careful not to get sprayed with hot coolant). If you smell coolant, suspect a leaking heater core. If you see a puddle of coolant on the floor, suspect a leaking heater core. Also, be sure to visually inspect the heater hoses under the hood while the car is hot (but not overheated) and the heater is on full blast. If you see a leak in a heater hose, that's at least one source of your leak.

Internal Leak Not Involving the Reservoir or Radiator Cap
If the cooling system fails the pressure test but no leak is observed and no coolant falls to the ground, it's possibly an internal leak through a breached head gasket or a breach in the separation between the radiator and the transmission fluid cooler. Such a leak would typically be one of these three:
• Coolant through the head gasket into the cylinders
• Coolant through the head gasket into the oil
• Coolant through the radiator into the transmission fluid
Voluminous white smoke out the exhaust, especially when starting, indicates coolant into the cylinders. Yellow or white foam or gunk on the oil cap indicates coolant into the oil, as does beads of water in the oil or a water film. Thankfully, water into the transmission fluid is rare. If the transmission fluid on the transmission dipstick looks good, coolant into the transmission fluid is probably not the problem.

Breached head gasket: combustion gas in the coolant pushing coolant out the reservoir
This is best detected with a combustion gas detection test, using either a smog sniffer or a block tester. There are different kinds of block testers, one of which is from NAPA and costs in the neighborhood of $45.00.

Bad radiator cap allowing coolant out the reservoir or cap
Observe the cap for cracks (in rubber or in metal) or swelling. Put your thumb on the base and fingers on the top of the cap and squeeze. If it's easy to squeeze, the radiator cap is bad and will probably lose coolant.

Existing overheat venting excess coolant through the reservoir
If the cooling system passes its pressure test, there's no evidence of a heater core or heater hose leak, the radiator cap is good, the block test indicates there is no combustion gas in the coolant, and there's no evidence of coolant in the oil, cylinders or transmission fluid, it's best to assume that the coolant loss was due to an overheat caused by something other than coolant loss. In that case, investigate the possibility of grossly malfunctioning engine, using the vehicle beyond its capabilities, and inadequate cooling system. All three are unusual. If it's none of those, treat this as an inability to adequately transfer heat.

Catastrophic Coolant Loss
If the upper or lower radiator hose breaks, or if the radiator ruptures, the car will be drained of coolant within seconds, and the temperature will rise precipitously. If such a car is not shut down within a minute of such a catastrophic coolant loss, a blown engine is the likely result. If you ever see smoke or steam coming out the hood while driving, pull over safely and shut it down instantly. Don't wait for the the next exit -- it's likely your engine will be ruined by then. Towing is expensive, but it's much cheaper than replacing an engine.

Inability to transfer heat
If a pressure test shows the root cause not to be a leak, and if the cause is not a grossly malfunctioning engine, usage beyond design, or weakly designed cooling system, then the problem is caused by an inability to adequately transfer heat. Now is the time to look for the cause of overheating within the closed system of your cooling system.
Here are some of the mechanisms of inadequate heat transfer:
• Circulation stopped by collapsed lower hose
• Circulation slowed and heat transfer retarded by excessive deposits in radiator
• Thermostat always closed, or opens at higher than specified temperature
• Coolant not able to absorb and carry heat
• Inadequate air flow through radiator
• Blockage in upper radiator hose (highly unlikely)
• Insufficient water pump pressure
• Blockages in water pathways within the engine block

Last edited by dragginwagon406; 03-31-2007 at 02:09 AM..
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Unread 03-31-2007, 01:50 AM   #3
dragginwagon406
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Join Date: Jul 2006
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Posts: 1,277
Circulation stopped by collapsed lower hose
As you can see from the preceding diagram, the water pump sucks water out of the radiator through the lower radiator hose, and shoots it into the engine block. That suction would cause the lower radiator hose to collapse if it weren't for the fact that a sturdy spring inside the lower hose prevents such collapse. A collapsed lower hose would prevent circulation through the radiator and quickly cause an overheat.
So with the car running and warmed up (but not overheated), visually inspect the hose and make sure it's not collapsed. With the car not running and the engine cool, feel the hose and make sure it's incompressible with your fingers. Also make sure it's not cracked or brittle.

SAFETY WARNING: When feeling hoses or in any way reaching into the engine compartment, wear eye protection and take reasonable precautions to prevent getting burned. Never allow your fingers, hands, hair, clothing, or other body part to come near the fan or belts. Remember that electric fans can suddenly turn on even if the car is not running and the key is not in the ignition.

Although a collapsed bottom hose would cause an overheat, it's possible that a massive radiator blockage caused the collapsed hose. If you see a collapsed hose and it appears to have been the correct hose (i.e. it has a spring but the spring failed), look very carefully for blockages in the radiator. Whatever the cause of the collapse, replace any bottom radiator hose that has ever collapsed, and be sure to fix whatever caused the collapse.

Circulation slowed and heat transfer retarded by excessive deposits in radiator
Radiator deposits and corrosion lead to blockage and overheat. In fact, many coolant losses and head gasket failures start out as simple radiator blockages. Detecting radiator deposits starts with the customer's symptom description. If the car's stable temperature has been slowly rising for weeks or months, radiator deposits are one possible cause. If the car ran at a specific temperature, then all of a sudden jumped to a higher temperature, radiator deposits aren't a likely cause. As in all deductions based on symptom descriptions, you must evaluate the customer's ability to relate the facts as they happened.
Most radiator deposits serious enough to push the temperature anywhere near redline are visually observable if you drain a few inches of coolant from the radiator. Other diagnostic tests include using an infrared temperature sensor to detect "hot spots" in a radiator. Such hot spots indicate places that are cooling efficiently (the hot coolant is flowing through them), as opposed to the "cool spots" that have no coolant.

Steve Litt's Radiator Opinions
In my personal opinion, a radiator with enough corrosion or deposits to make it a likely cause (not THE likely cause, just A likely cause) of overheating, should be replaced with a higher capacity radiator. The preceding sentence assumes that the customer wants to keep the car. Before the customer can decide whether he wants to keep the car, the customer needs to know whether there's a head gasket problem, so a block test, visual inspection of the car's exhaust, visual inspection of the transmission's dipstick, visual inspection of the oilcap, and a pressure test should all be performed to determine the likelyhood of a broken head gasket.

You noticed I said replace the radiator, not "rod it out". I'm of the opinion that oftentimes "rodding out" does not cure the problem, and in many other instances it cures the problem for only a few months. "Rodding out" is labor intensive and not cheap. The extra money spent on a brand new radiator is money well spent in my opinion.
And in my opinion, there's no such thing as too much radiator. Get the biggest one you can. A huge radiator can, in some cases, compensate for suboptimal conditions:
• Long, steep grades
• 100+ degree weather
• Accidentally running with too little coolant
• Towing
• Small head gasket breach (at least for a short while)
• Severely mistuned or misrepaired engine
• Missing fan shroud

When I say "a huge radiator", area counts more than thickness. I'd much rather have a 24x16 two row than a 12x16 four row, but certainly all other things being equal, a four row is better than a two row. When getting huge radiators keep in mind that when the radiator extends beyond the area that can be ventilated by the grill, the benefits of big area are decreased.

If you're a car owner, upon hearing that your current radiator is seriously corroded, deposited or plugged, I'd advise getting the biggest possible radiator. If you need to spend extra money to have a huge radiator manufactured, that's a good idea, assuming you have confidence in the outfit doing the manufacturing.

NOTE:
When replacing a radiator, it's best to use a similar type of radiator, but bigger. For instance, if the original radiator was aluminum, it's best to make the new radiator aluminum. Try to replace plastic radiators with bigger plastic radiators. If you need to use a different type replacement, be aware that you might need to change the type of antifreeze you use.
If you're an Automotive Technician, try to get your customer to see the value in a huge, brand new radiator.

Thermostat always closed, or opens at higher than specified temperatures
If the thermostat remains closed at all times, no coolant will enter the radiator, and the engine will overheat. If the thermostat opens only at an excessively high temperature, the engine will remain at that temperature, and if that temperature is hot enough to cause coolant loss, additional overheating will result.

You can deduce when a thermostat opens by a number of means, including feeling for pressure changes on the upper hose, or viewing water flow through the radiator. SUCH VIEWING SHOULD BE DONE IN A SAFE WAY -- warm but not hot, eye protection, do not lean over the radiator.

Once you can determine the opening and closing of the thermostat, measuring the engine temperature with a thermometer can tell you the opening temperature. I've never measured the temperature this way. Many techniques exist, but I can't vouch for any particular techniques.

Thermostats typically malfunction by one of two mechanisms:
• Thermostat cannot sense water temperature because of a gas bubble
• Defective thermostat

Perhaps the easiest way to rule out all thermostat problems is to run without a thermostat for an hour or so. If overheating ceases, your thermostat is involved in one way or another. If overheating continues (but perhaps taking longer to happen), the thermostat is ruled out as a cause. If the thermostat appears to be at fault, you might try putting it in a pot of hot water and see if it opens at the correct temperature. If it does, the thermostat is probably not defective, meaning that you might have a gas bubble problem.

NOTE: Running without a thermostat is a diagnostic test, not a solution. To reduce the risk of engine damage, "thermostatless" operation should occur for the minimum time necessary to reproduce an overheat, or confirm that the overheat does not occur in the absence of a thermostat.

Many people have successfully cured gas bubble problems by drilling a 1/8" hole in the thermostat. This hole lets the gas rise past the thermostat, allowing the thermostat's wax temperature sensor to once again contact coolant. However, it's possible that such a hole could cause some problems, so you might want to weigh that possibility.
Here are the instructions one Troubleshooters.Com visitor, A.S.E. certified master truck and auto mechanic Dennis Buler, gave me for drilling the 1/8" hole:


Top view of thermostat. The violet dot at the 12 o'clock position of the rim is where Dennis recommends drilling the 1/8" hole.
Side view of thermostat
Bottom view of thermostat
Dennis' exact words were "i drill the hole in the flat disk part like half way between where the gasket would seal and the center opening mechanism".
One more thing. Remember that a gas bubble can be caused by combustion gasses passed through a head gasket breach. In such a case it's likely you'll need to replace your head gasket.

Coolant not able to absorb and carry heat
When I was younger and less wise, I drained the cooling system of my 1973 Ford Country Squire and replaced it with 100% ethylene glycol (antifreeze). The car overheated badly. 100% ethylene glycol is a poor absorber of heat. 100% propylene glycol is a somewhat better absorber of heat, and in some cases is useful as a coolant. But it doesn't absorb as much heat as 50/50.

At temperatures below the boiling point of water, water is more effective at absorbing and carrying heat than any mixture of water and either ethylene glycol or propylene glycol. If you have a 160 degree thermostat and your cooling system is functioning well, you could theoretically add cooling capacity by replacing your water/antifreeze mixture with pure water.
But the added cooling capacity would be short lived indeed. Adding antifreeze gives the following benefits that water alone cannot:
• Higher boiling temperature at a given pressure
• Lower freezing temperature
• Corrosion resistance

You need coolant capable of absorbing and carrying heat. Pure ethylene glycol is not such a coolant. Pure propylene glycol is barely adequate. Pure water will absorb and carry heat very well, but if your engine is designed to run hot, your water will boil away, causing an overheat. Additionally, pure water will lead to a cracked block in cold climates, and excessive cooling system corrosion in any climate.

Always know what you're using for coolant. If you know there's no propylene glycol in the coolant mixture, you can use a simple specific gravity indicator to deduce your mixture. The ideal mixture is 50/50, but in extremely cold climates you can get by with 70% antifreeze and 30% water. Any more antifreeze will lead to overheating.

If there's a likelihood that some or all of your coolant is propylene glycol, specific gravity measurements will not accurately indicate your mixture. Use a refractometer instead.

If the coolant is so old that the driver does not know what all is in it, perhaps it's time to flush the cooling system and replace it with whatever the car's manufacturer recommends. Coolant is discussed in more detail later in this magazine.

Inadequate air flow through radiator
No matter how well heat is transferred to the radiator, unless the radiator is cooled by air flow, the cooling system will not function. At moderate and high driving speeds, air is forced through the radiator as the car pushes through the air. At idle and low driving speeds, a fan is required to ventilate the radiator with cool air. Therefore, when a symptom description mentions overheating at low speed, idle, or stop and go traffic, the fan system should be investigated first.

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The Fan System
There are mechanical fan systems and electrical fan systems. Transverse engines have electrical fan systems because of the difficulty of having a belt turn a right angle to operate a front-facing fan. Electrical fan systems are comprised of a fan attached to the radiator (on the engine side), and electronics to turn the fan on and off as needed. If the electronics malfunction such that the fan never comes on, overheats at slow and idle will be the result. If that's suspected, there are ways to jumper the fan so it's always on. Be sure to check electrical diagrams so as not to inadvertently damage the fan control electronics. If the jumpered fan runs and the overheat goes away, the problem is in the electronics or in whatever senses the temperature. If the fan doesn't run even after jumpering it directly across the battery, the fan is defective. Either way, jumpering the fan is a temporary diagnostic test, not a solution. Immediately fix the root cause -- don't continue to use a car with a jumpered fan.

Most cars with forward facing engines use a mechanical fan system, consisting of the fan, fan clutch, fan belt, and radiator shroud. On such a system the fan belt turns the fan clutch, which turns the fan, which pulls air through the radiator, constrained by the radiator shroud.

If the fanbelt slips, it can't deliver necessary torque to drive the fan at sufficient speed, and idle/low speed overheating can result. The fan clutch is designed to deliver more torque at higher temperatures. If it doesn't function right, it doesn't transmit enough torque to drive the fan at sufficient speed, and idle/low speed overheating can result. The fan shroud is like a tunnel between the fan and the radiator, ensuring that all air pulled by the fan comes through the radiator, instead of simply being sucked from the surrounding area or around from the back of the fan. Without a fan shroud, idle and low speed overheating is likely to occur.

You might wonder why a fan shroud is necessary on a mechanical fan when it's not necessary on an electrical fan. An electrical fan is mounted to the radiator itself. It's very close to the radiator, and moves with the radiator. Contrast this with the mechanical fan, which must be mounted several inches away from the radiator. Because the mechanical fan moves with the engine, and not with the radiator, installing the mechanical fan close enough to eliminate the need for the fan shroud would cause the fan to gouge the radiator when extreme engine torque causes the engine to move. This is especially true when a motor mount is broken.

Other impediments to cool air through the radiator
Other impediments to cool air through the radiator can cause overheating at all driving speeds. One such impediment is the air conditioning cooling coils, which typically sit right in front of the radiator. Obviously, the air conditioning coils restrict the flow of air to the radiator, but more important, if the air conditioner is on, the air conditioning coils get very hot, heating the air intended to cool the radiator. It's like driving on a 120 degree day. Add to that the fact that air conditioner consumes power that must be provided by burning more gasoline, and it becomes obvious why you should turn off your air conditioner during mountain travel.

Bugs, dirt and debris can clog the air flow passages of your radiator, or of the air conditioner cooling coils before the radiator. Either way, airflow is restricted, and overheating can result. There are methods of cleaning the radiator and cooling coils, but be very careful not to damage the delicate tubes and vains. Also, these areas are often difficult to access. Sometimes compressed air is the best way to clean them. Once cleaned, you might want to install a "bug catching net" in your grill, especially in climates where there are numerous flying bugs.

Radiators are typically constructed with tiny tubes soldered to fins, or else oval tubes. Either way, the idea is to allow air to flow through the radiator. If these things become bent, air flow is impeded. Bent tubes and fins can be straightened, but trying to do so can also further damage the radiator or cause a leak. Radiators should be handled delicately.

Another impediment to air flow is a damaged radiator. Vains and tubes are bent and twisted by crashes and mishandling of the radiator by inept technicians. Another cause of radiator damage is fan damage, in which a mechanical fan hits the radiator. The primary cause of fan damage is a bad motor mount, so always maintain your motor mounts.

In general, you might deduce impediments to cool air by observation, or lacking that by seeing how well compressed air goes from the outside of the grill to the area between the radiator and the engine. On my 1988 Buick Park Avenue with air conditioning, when I put the blowing end of a 5HP industrial vacuum on the grill, I could feel the breeze on my hand inside the engine compartment, but just barely. If you have an easy way of removing your grill, perhaps the best and quickest test is to investigate is visually. Even if the air conditioning cooling coils block your view of the radiator, it's a good bet that if the air conditioning coils are clean, so is the radiator.
A complete radiator investication involves removal of the radiator, which is labor intensive and should only be done when there's good reason to strongly suspect dirt on the radiator or bending of the radiator's components.

Blockage in upper radiator hose (highly unlikely)
This is so unlikely that it should be tested only in cases of unexplained overheating. The test might be to let the car cool, then disconnect the upper radiator hose from the radiator, at which time you'd lose coolant. If there appears to be a blockage, replace the hose. Once again, this is highly unlikely.

Another extreme unlikelihood is that the water pump is pushing flow backward, so that there's suction on the upper hose. This could conceivably happen if a water pump made for a serpentine belt is used with a belt off the crankshaft, or vice versa. Reversed pump direction would likely cause other strange symptoms.

Insufficient water pump pressure
If the water pump can't circulate the coolant, the car will overheat. Not only that, but the pressure and flow must be sufficient to support high velocities through the radiator. It's important that the coolant experience turbulance in the radiator tubes, so that all the hot water contacts the tubes. Turbulance can occur only when coolant velocities are above a certain level.

That being said, the water pump's job is to circulate coolant through a well functioning system, not to brute force coolant through a radiator whose tubes are clogged with deposits. There's no easy and accurate way to assess the level of water pump functioning. Here are some things that can go wrong with a water pump.
• Bad belt or wrong tension
• Bad bearings
• Undersized or oversized pulley
• Bad impellers

Belt tension can quickly be checked by hand. Bad bearings can often be deduced by manipulating the water pump shaft to determine whether there is play. Further confirmation can be had by loosening the belt driving the water pump, and seeing if the pump turns reasonably free. Be careful not to stretch the belt -- loosen a component, do not strongarm the belt off the pulley.

An undersized or oversized pulley can be deduced by obtaining the manufacturer's documentation, or by comparing the pulley to what the manufacturer put in similar cars. Be sure the similar car is similar enough. For instance, if your water pump is driven by a serpentine belt, make sure you compare it to a similar model and year with a serpentine belt. An oversized pulley causes the pump to turn too slowly, thus reducing coolant flow, possibly to the point of overheat. Note that theoretically the overheat should be speed independent because high speeds require faster coolant flow. But that's just theory.

One might think that an undersized pulley would cause the pump to spin faster, thereby increasing coolant flow. While this may be true for a moderately undersized pulley, if the pulley is significantly undersized it's just as likely to present so much torque, and so little traction area, that the belt will slip, causing a vast decrease in coolant flow -- probably at high speeds where coolant flow is most crucial.

Blockages in water pathways within the engine block
This is very hard to determine without partially disassembling the engine. For this reason the best way to "rule out" blockages is to find a different cause. Luckily such blockages are usually localized and may not harm the engine excessively. Moderately quick diagnostic techniques that are at least a little useful include using an infrared thermometer to try to find "hotspots" on the engine, and removing spark plugs to see if any show symptoms of excessive heat.
Because internal blockages in the engine block or heads are so hard to diagnose, it's best if they never happen. Practicing corrosion protection and impurity protection is probably your best defense.

Root Cause Drilldown
So far this article has explained most common mechanisms by which an overheat can occur. But these mechanisms also have root causes, and an understanding of these ultimate root causes is essential for constructing an economical preventive maintenance plan and for constructing economical diagnostic procedures.
This section discusses four lower level causes, as well as their ultimate causes and effects. Those three lower level causes are:
• Corrosion
• Breached head gasket
• Radiator damage
• Normal wear and tear

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Corrosion
Corrosion can cause the following overheating mechanisms:
• Radiator leaks
• Radiator deposits and blockages
• Heater core leaks
• Heater blockages
• Hose deterioration (through electrolysis, in conjunction with heat, age and vibration)
• Head gasket breaches
• Water pump failures
• Thermostat failures
• Engine "hot spots"

As you can see, preventing corrosion goes a long way toward preventing overheats.

Corrosion happens when the coolant loses its anticorrosive properties. With standard antifreeze in a 50/50 mixture this happens in about 2 years or 24,000 to 30,000 miles. Same with 50/50 propylene glycol or 100% propylene glycol. There are several "extended life" antifreezes. Some, such as the GM "Dex-Cool" complient antifreezes (Texaco/Havoline Dex-Cool and Prestone Extended Life 5/150), are designed to go 5 years or 150,000 miles between changes. Many new GM cars come from the factory with this type of coolant. However, "long life" coolants often revert to 2 years when mixed with other types of coolants, or when used in a system with trapped air or rust/corrosion. Mixing antifreezes is generally a bad idea, and certain combinations can actually promote corrosion.

Furthermore, encroachment of combustion gasses into the coolant via a head gasket breach can neutralize any coolant's corrosion inhibition long before the specified life.

Most antifreeze is extremely cheap. My local Discount Auto Center sells Prestone brand Ethylene Glycol standard antifreeze for $6.99 a gallon, and Havoline Dex-Cool for the same price. You can get 3 gallons of high quality ethylene glycol antifreeze for $21.00. Propylene glycol is less likely to poison animals and is a little more costly, as are the various more exotic antifreezes. In my opinion, it's time flush and change your antifreeze when:
• You see any rust in your antifreeze, and it's been over 4 months since your last coolant replacement
• Corrosion or deposits are detected in your radiator, and it's been over 6 months since your last coolant replacement
• Different types of antifreezes have been mixed
• The cooling system needs service or diagnosis and the exact type and mixture of the coolant is unknown
• Your cooling system needs service requiring a major draining of coolant
• Somebody has used a "leak seal" type of product in the cooling system (these are usually temporary stopgap measures, and often clog passages and components leading to further problems).

I personally believe that unless you know for certain that your cooling system is in perfect shape and always has been, you should flush and change your coolant yearly. It's such a low price for preventing corrosion. I personally believe that if you're using a 5 year/150,000 mile coolant, it's best to change it every 3 years or 90,000 miles once the car is out of warranty. If you have reason to believe there's air, gasses, impurities, deposits or rust in the coolant, 2 year or 1 year intervals might be even better.

While we're on the subject of economics of corrosion protection, distilled water is just too cheap not to use, assuming you're a car owner doing your own work. Distilled water costs about $0.70 per gallon, so for about $2.00 per year you can give the anticorrosives in your antifreeze a fighting chance by not introducing calcium, lime or who knows what into your cooling system. This is especially important if your antifreeze uses phosphates as a corrosion inhibiter, because phosphates react with calcium to produce radiator-clogging scale. Naturally, if you find yourself low on coolant and need to get home, use tapwater. Never use softened water, as it contains salts that can quickly corrode your cooling system.

If you can conquer the corrosion monster, you're most of the way to making sure your car never has a single incident of overheating.

Breached Head Gasket
A breached head gasket can cause the following:
• Overheating
• Loss of coolant, with or without overheating
• Corrosion of the cooling system
• Destruction of the oil's lubricating properties
• Breakage of the starter, solinoid or flywheel

The most common cause of breached head gaskets are overheats. Even a single overheating incident can break a head gasket, especially in a car with a bimetalic engine. The best way to protect against an overheat is to take proper care of your cooling system, and to look at your temperature gauge often. If your car has an idiot light instead of a temperature gauge, installing an aftermarket temperature gauge is an excellent investment.

Radiator Damage
Radiator damage retards proper air flow through the radiator, thereby causing or contributing to overheating. Also, radiator damage can cause leaks, either immediately following the damage, or months or years later. Here are some ways to lessen the chance of radiator damage:
• When doing your own work, handle the radiator like the fragile piece it is
• Use only competant automotive technicians
• Don't crash your car, and if you do, replace a damaged radiator before it can cause overheating
• Check motor mounts frequently, and replace them when they break

A broken motor mount can allow the fan to rip through the radiator. Typical causes of premature failure of motor mounts are aggressive driving and bad shocks.

Normal Wear and Tear
Things wear out. Many of those things can cause overheats if they break. As we've seen, even one overheat can severely damage a car. Many of the components that can cause overheat when they wear out are cheap. They should be replaced in a preventive maintenance program:
• Belts
• Hoses
• Hose clamps
• Thermostat
• Radiator cap
• Coolant

By replacing these cheap and easy components on a regular schedule of preventive maintenance, you limit the likelihood of damaging expensive parts such as the radiator, water pump, head gasket, heads, or engine.

Summary
This article discussed the common mechanisms by which an overheat occurs, and discussed root causes of many of those mechanisms. As this article strongly implies, the best way to avoid overheats is by a program of preventive maintenance.
Steve Litt is the author of Rapid Learning: Secret Weapon of the Successful Technologist. He can be reached at Steve Litt's email address.

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Unread 03-31-2007, 01:59 AM   #6
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Preventive Maintenance of Cooling Systems
By Steve Litt

As you can imagine from the preceding article, cooling system preventive maintenance can make the difference between a reliable car with few problems, or a lemon with huge yearly shop costs. If you figure the yearly cooling system preventive maintenance costs $100.00, and you drive 10,000 miles per year, you're spending a penny a mile to keep your. If the two year maintenance costs another $100.00, that adds a half a cent a mile. And if the three year maintenance costs $150.00, that adds another half penny. So for two cents a mile you can keep your car overheat free for a good long time.

The sad thing is that most people won't spend the money. Two cents per mile doesn't sound like much, but when you spend it all at once, and when you're spending it on a car that seems perfectly healthy, many folks feel it doesn't make much sense. If you're an automotive tech, your job is to explain why it does make sense. Explain that the customer's car may only seem healthy. Cooling system problems are a disease with a long incubation period. It can take 4 years for radiator corrosion and deposits to reach the point where they compromise everyday driving.

But once the symptoms appear, they're often relentless. That clogged radiator, if not replaced in time, can lead to a head-gasket busting catastrophic overheat. And if the head gasket isn't diagnosed correctly, replacing the radiator doesn't completely eliminate the symptom. The customer begins to believe his car is possessed by the overheating demon.
The radiator isn't the only component being compromised. Old coolant corrodes the water pump, leading to failure. And you know how replacement water pumps are -- they're seldom as good as the original, so after the first replacement, water pumps become a regular maintenance item at a couple hundred a pop.

An undiscovered bad hose can break, and unless the car's driver has the sense to safely pull over and shut it down immediately, the head gasket will be breached.

Check your motor mounts often. A broken motor mount can allow a mechanical fan to slice into the radiator. This can render the vehicle undriveable, or it can simply reduce the excess cooling capacity to the point where the vehicle will overheat in challenging driving conditions.

Preventive maintenance can't necessarily prevent all these problems, but it can usually postpone most of them until well past the car's first decade, and such preventive maintenance makes it likely that any cooling system problems will be caught before heads or head gaskets are damaged.

This article contains an example of a cooling system preventive maintenance program. I'd imagine it costs about two cents a mile, and will probably enable the cooling system to be problem free for its first decade, and limit problems to minor repairs thereafter.

If I ran an automotive shop, I'd package the yearly, two year and three year maintenance items for a fixed price, and sell them to customers as peace of mind. It takes a little education, but it's worth it in dollars and cents and in customer goodwill. Note that much of this maintenance overlaps other maintenance, such as oil and lube and transmission, so it could be combined with those. Finally, by keeping track of the customer's maintenance, the shop can provide a valuable service to customers with better things to remember than exactly when they last replaced their thermostat or belts. Also, by providing that service, the shop can maximize the likelihood that the customer will use the shop for all work, and not grind for the lowest price.

Troubleshooters.Com Suggested Yearly Preventive Maintenance (or every 15,000 miles, whichever's first)
This looks like a lot, but most of it is easy inspection. Because of the nature of the 2 and 3 year maintenance items, these inspection items are unlikely to uncover problems after the first yearly inspection. The only parts involved in the yearly maintenance are the radiator cap and the coolant.
• Bounce test the shocks (to insure protection motor mounts)
• Inspect belts for wear and tension
• Check function of serpentine tensioner arm
• Inspect hoses for excessive mushiness, excessive hardness, brittleness or cracking. By feeling from the outside, inspect hoses for internal gaps that might indicate electrolytic breakdown. Also inspect hoses for evidence of leaks.
• Inspect inside of radiator for corrosion and to verify reasonable coolant flow.
• To the extent possible without extensive labor, inspect exterior of radiator and air conditioner cooling coils for dirt and damage. Clean as necessary.
• Inspect water pump for leaks and excessive shaft play or binding
• Revv test the motor mounts (to insure protection of radiator in a mechanical fan system)
• Verify that the engine maintains a temperature within manufacturer's specification
• Verify that the thermostat is opening and closing at approximately the right temperature
• Verify that the temperature gauge is reasonably accurate
• Verify that the electrical fan turns on at the right temperature, or
• Verify that the mechanical fan spins and its fan clutch is in good working order
• Verify proper heater function
• Verify the absense of white or yellow foam or gunk on the oilcap
• Verify the absense of steam in the exhaust, especially on startup
• Verify clean and pure transmission fluid
• Verify clean and pure coolant with no rust or other impurities
• Perform a pressure test
• Replace Radiator Cap
• Thoroughly backflush and replace the coolant (or else drain radiator and replace with new coolant twice yearly)

Troubleshooters.Com Suggested Every Two Years Preventive Maintenance (or every 30,000 miles, whichever's first)
I'd imagine thermostat replacement plus testing for combustion gas could be done for less than $100.00. As long as high quality thermostats are used, I'm of the opinion that this would make thermostat failures almost obsolete, and it would hopefully detect bad head gaskets long before they contributed to the destruction of other components. Given the yearly maintenance, it's doubtful that combustion gas would be found.
• Test for combustion gas in the coolant
• Replace the thermostat

Troubleshooters.Com Suggested Every Three Years Preventive Maintenance (or every 45,000 miles, whichever's first)
Unless a driver is very well informed, a broken water pump belt or a broken radiator hose will lead to a catastrophic overheat. Even if the customer seems intelligent enough to safely pull over and shut down upon first detection of a cooling problem, all sorts of teenagers might be driving the car. Unless the car is shut down within a minute or so of the dropped belt or ruptured hose, severe engine damage will result. The money saved by trying to extend belt and hose life past three years isn't worth the problems that result if the life estimate proves too optimistic.
• Replace any belts that have not been replaced in the past 2 years
• Replace top and bottom radiator hoses that have not been replaced in the past 2 years

Steve Litt is the author of "Troubleshooting Techniques of the Successful Technologist". Steve can be reached at Steve Litt's email address.


Optimizing Overheating Diagnosis
By Steve Litt
As the webmaster of Troubleshooters.Com, I've gotten dozens of letters that go something like this:

My car overheated , so I took it to the shop. They replaced the thermostat. I drove it for a few days and it overheated again. They then charged me another $200 to replace the water pump, but as soon as I got the car home it overheated so badly that it wouldn't even start. This time they rodded out the radiator for $150, and it got better, but still overheated. So they charged me another $200 to replace the radiator with a new one (and told me they were giving me a break on the price). That improved the situation even more, but it still overheats on long trips, and it runs rough and there's a lot of white smoke coming out the exhaust. When I took it back to the shop they said it was a broken head gasket, and it would cost $1200 to fix. What do I do?

It's entirely likely that the original root cause was the radiator, and nothing but the radiator. But during the time consumed by diagnosis by serial replacement, successive overheats broke the head gasket, thereby adding yet a new overheating cause. Or take the case of an even less competant shop:

My car overheated, so I took it to the shop. They replaced the thermostat, but it still overheated. They then charged me another $200 to replace the water pump, but nothing changed. So they replaced the radiator, but everything was still as bad. Yesterday I took it to another shop, who told me the white foam on the oil cap and steam coming out the exhaust indicates a broken head gasket, which was caused by all the overheating. And they told me I have a collapsed lower radiator hose, which probably caused the original overheating, and that the cost to install a replacement hose would have been $50. Could this be true?

Diagnosis by serial replacement is NOT an option if you want to have a profitable shop over the long term. Although some components are hard to test (water pumps, for instance), enough easy tests are available that you can usually pinpoint the root cause if you do all the simple tests. Another reason to do a full scale diagnostic workup is that by the time you see a typical overheat, multiple causes may be at work.

The following outline lists and categorizes relatively cheap and simple tests that will maximize the probability of accurately identifying the root cause, thus preventing costly and credibility busting diagnosis by serial replacement:
• Symptom description
o When did the overheating start?
o Was the onset of overheating gradual or sudden?
o What situations tend to make the overheating worse?
o Does it happen more at idle, low speeds or stop and go traffic? (suspect fan system)
o How long does it take to overheat?
o Has the overheating ever caused the car to stall? (suspect head gasket as a consequential damage)
o Does the engine temperature tend to go up and down as you drive? (suspect head gasket as a cause)
o Does it overheat once, and then return to normal for the rest of the drive? (suspect head gasket as a cause)
o Have you seen puddles of liquid where you've parked? (suspect leak)
o How long do you go between cooling system flushes (if never, suspect corrosion)
o Do you see steam? Where does it seem to come from?
o Describe anything you've seen, heard or smelled.
o Do you have any other observations you think might have anything to do with this overheating?
• Symptom reproduction
o Compare engine temperature with manufacturer's spec when running car according to customer's description of the symptom's reproduction sequence
o Verify that the temperature gauge is reasonably accurate
o Verify other specifics of the symptom description
• Evaluate Head Gasket Function
o Verify the absense of white or yellow foam or gunk on the oilcap
o Verify the absense of steam in the exhaust, especially on startup
o Verify clean and pure transmission fluid
o Verify clean and pure coolant with no oil, rust or other impurities
o Test for combustion gas in coolant at radiator fill pipe and at reservoir
• Did coolant loss cause overheat, or did overheat cause coolant loss?
o Perform a pressure test, locate any leaks
o Observe and test radiator cap
• Evaluate fan system
o Ask customer whether it tends to overheat more at idle, slow speeds, or stop and go traffic
o Verify that the electrical fan turns on at the right temperature, or
o Verify that the mechanical fan spins and its fan clutch is in good working order
o Check fan belt driving mechanical fan
• Research fanbelt related causes
o Inspect belts for wear and proper tension
o Check function of serpentine tensioner arm
• Radiator, water pump and thermostat
o Inspect water pump for leaks and excessive shaft play or binding
o To the extent possible without extensive labor, inspect exterior of radiator and air conditioner cooling coils for dirt and damage. Clean as necessary.
o Inspect inside of radiator for corrosion and to verify reasonable coolant flow.
o Verify that the thermostat is opening and closing at approximately the right temperature
 Both by pressure increase in top hose, and by viewing coolant flow through radiator
• Heater
o Verify proper heater function
o Look for coolant on the floor in passenger compartment, smell for coolant smell in passenger compartment
• Prevent and predict future problems
o Inspect hoses for excessive mushiness, excessive hardness, brittleness or cracking. Inspect hoses for internal gaps that might indicate electrolytic breakdown. Also inspect hoses for evidence of leaks.

Steve Litt is the author of Rapid Learning: Secret Weapon of the Successful Technologist. He can be reached at Steve Litt's email address.

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Unread 03-31-2007, 02:00 AM   #7
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Coolants 101
By Steve Litt

One could write a PHD thesis on coolants. This article simply strives to give a layman's overview of the subject.
Automotive coolant is a mixture of two liquids:
• Water (ideally distilled)
• Antifreeze

The antifreeze consists of two types of components:
• Freeze inhibitors
• Corrosion inhibitors

Current antifreeze products inhibit freezing with either ethylene glycol or propylene glycol. The former is a better freeze inhibitor, boils at a higher temperature, and in a 50/50 to 70/30 mixture with water is a better absorber of heat. The advantage of propylene glycol is it doesn't smell or taste as sweet, so animals and small children aren't as tempted to drink it. This is important, because both ethylene glycol or propylene glycol are lethally poisonous in small quantities. The other advantage of propylene glycol is that in a pure form it absorbs enough heat to be useful as a coolant, whereas pure ethylene glycol is not useful as a coolant in its pure form.

Propylene glycol/water mixtures have the disadvantage of not being measurable with a traditional specific gravity measurement tool. Instead these mixtures must be measured by the much more expensive refractometers. And, as previously mentioned, at all but the most concentrated mixtures, ethylene glycol solutions are more efficient coolants.
"Ordinary" antifreezes use ethylene glycol as their freeze inhibitor. "Environmental" antifreezes use propylene glycol. Most of the new "long life" antifreezes use ethylene glycol. They derive their long life from their corrosion inhibitors, not from a special freeze inhibitor.

Corrosion Inhibitors
As freeze inhibitors react with air and other chemicals over time, they become acidic. This causes corrosion to the metal parts of the cooling system, and in fact can turn the whole system into a battery whose anodes (typically the aluminum parts) are consumed. Within a very short number of years, the radiator, water pump, and even the hoses are corroded and clogged. Once that happens, the overheating begins, leading to a broken head gasket or worse if the compromised parts are not replaced. Corrosion protection is THE biggest factor in keeping a cooling system healthy. Which is why antifreeze comes with corrosion inhibitors.

Ordinary "2 year" antifreezes use borates, phosphates and/or silicates as corrosion inhibitors. Most North American standard antifreezes contain phosphates, which are great at corrosion protection, but can react with calcium in tap water to produce radiator-clogging sentiment and scale. The harder the water, the more of a problem this becomes. If you change your own coolant, you can avoid this by using only distilled water. At less than a dollar a gallon, it's a bargain.
Never use softened water in a cooling system. Softened water contains salt (NaCl), which becomes conductive in water and turns your entire cooling system into a battery, destroying first your aluminum parts, and then going to work on even the cast iron.

The new "extended life" antifreezes are the same as conventional antifreezes except for their corrosion inhibitors. Most "extended life" antifreezes use organic acids instead of inorganic salts (borates, phosphates and silicates) for corrosion protection. When used correctly, these organic acids are said to protect against corrosion for up to 5 years and 150,000 miles. There have been a few reports of problems with corrosion on lead-soldered copper/brass radiators protected with organic acids, and also a few reports of sludging with organic acids. These are discussed in more detail in some of automotive author Larry Carley's writings (URL in this magazine's URL's section). The two organic acid technology antifreezes approved by GM are Texaco/Havoline Dex-Cool and Prestone Long Life 5/100.

From the car company's point of view, organic acid corrosion inhibitors are great way to protect against warranty problems caused by customer neglect. Most warranties are over by 5 years or 150,000 miles. Once your car is out of warranty and you are responsible for its upkeep, even if your car came with extended life antifreeze there's no reason you can't change the antifreeze more often. That way, if conditions are less than perfect, you're improving your cooling system's chances. Texaco/Havoline Dex-Cool was selling for $6.99 a gallon at my local Discount Auto Parts store -- the same price as conventional Prestone antifreeze.

Coolant Replacement Recommendations
In my opinion, unless you have a very good reason to do otherwise, you should use the manufacturer recommended antifreeze for your car. The manufacturer has chemists and engineers on staff to figure out the exact best formula to use with the components in your car model. It's absurd to think that either you or an automotive technician could second guess them in ordinary circumstances.

So what would constitute a very good reason? One would be a radiator replacement with a substantially different radiator type. For instance, if the original was plastic and you put in an aluminum radiator, you'd need to totally reevaluate your choice of coolant, as this is something the car company's engineers did not design. Likewise, if the original was lead soldered copper and you're replacing with plastic. The list goes on.

Another good reason would be a known design defect involving a specific antifreeze. Certainly if the manufacturer later changed their antifreeze recommendation for a specific model, you should follow the new recommendation. And in certain circumstances where experts believe that the manufacturer was wrong, and your car is now out of warranty, you may decide to take the risk of going against the manufacturer's recommendations.

Never mix antifreezes. At best this would eliminate the long life of long life antifreezes, at worst it could cause a new corrosion problem worse than either of the antifreezes by itself. When you switch antifreeze types, you must totally drain the old antifreeze.

Steve Litt is the author of Rapid Learning: Secret Weapon of the Successful Technologist. He can be reached at Steve Litt's email address.

Last edited by dragginwagon406; 03-31-2007 at 02:36 AM..
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Unread 03-31-2007, 02:01 AM   #8
dragginwagon406
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Do It Yourself Coolant Changes
By Steve Litt

If you're old enough to remember coolant changes before the age of environmental law, all I can tell you is "everything's changed". Letting the engine run for 30 minutes, with the radiator petcock open and a garden hose pumping water into the radiator fill pipe is now seriously illegal. In most locales, all drained coolant must now be collected and taken to a licensed disposal facility. If the drained coolant is diluted with a garden hose, you might have 100 gallons to bring in :-).

The environmental laws change everything. What was an easy 20 minute procedure is now a day-long affair, complete with risks of injury, car damage, and legal difficulties. For that reason I've split this article in two sections:
• Traditional do it yourself backflush/replacement changes
• Easier coolant maintenance methods

I recommend the easier coolant maintenance methods. The reason the traditional methods are discussed first is so you understand all the hassle that goes along with the traditional methods. After reading the time, expense, difficulty and legal risks of traditional changes, I think you'll be ready to accept some of the disadvantages of the easier coolant maintenance procedures. And once again, nobody said the traditional change methods are difficult in and of themselves -- they're just incredibly difficult to do legally.

Traditional do it yourself backflush/replacement changes
Probably the toughest part of changing your coolant is disposing the old coolant in a safe and legal manner. Ethylene glycol is a potent poison that smells and tastes sweet, so if left in a pan or on the ground animals and small children will drink it and die. Propylene glycol isn't as sweet so it isn't as tempting, but it's still a poison.
Before starting your coolant change, make sure you read this whole article and note the extreme hassles, damage risks, legal risks, and personal injury risks in draining a cooling system in an environmentally responsible way. Check with your city or county as to the lawful coolant disposal procedures. Sometimes those procedures are costly enough that you're better off having a shop do your coolant change.
1. Pre-Drain procedures
2. Drain the reservoir
3. Drain the cooling system
4. Install the flush kit
5. Flush
6. 2nd Drain
7. Add Coolant
8. Close system
9. Test

Pre-Drain procedures
There exist various cooling system cleaners and flushers. The idea is that you add this liquid for 10 minutes and idle with the heater on full blast, or with some cleaners run the car for 6 hours and then drain and flush. I cannot comment on possible harmful side effects of these cleaners and flushers. I wouldn't use them on a car that has had annual coolant changes. They might be indicated on a car whose coolant is rusty, or a car whose radiator is partially clogged. If you use these cleaners or flushers, try to research any possible side effects.

Drain the reservoir
There are various ways to do this, including removing and inverting the reservoir (pour it into a container for disposal), or finding a way to drain it via the hose to the radiator fill neck. Another way would be to drain some coolant, run the car until it's well warmed up (but never overheated), and shutting down the car. The coolant in the reservoir should be sucked back into the radiator. You can also syphon the reservoir contents into a disposal container, but NEVER syphon by mouth, because antifreeze is a potent poison that can be fatal. After draining the reservoir, clean it by running a garden hose into it to remove dirt.

Drain the cooling system
Always make sure old coolant is poured into a pan -- never let it run into the ground or down the driveway and into the storm sewers. Antifreeze is a sweet tasting poison, and it kills animals and even small children. Never let the pan you drained it into remain unobserved, or a neighborhood dog or cat might die. Pour the contents of the pan into closed containers, and if your county provides a liquid waste drop off center, bring the containers there. Always conform to your city or county's laws concerning antifreeze disposal.
It seems like everyone has their own technique for draining the cooling system. Here are a few:
• Successive half-dilution
• Single half-dilution
• Running quick empty
• Running quick empty with thermostat removed
• Simultaneous draining of radiator and engine

Successive half-dilution
The most common seems to be the successive half-dilution technique. This technique involves waiting for the radiator to cool, removing the radiator cap, draining the radiator through the radiator petcock, filling the radiator with pure water, running the engine til hot with the heater on full blast. Every time this procedure is done the amount of antifreeze in the system is cut roughly in half, because at any one time about half the coolant resides in the radiator and the other half in the engine and heater. Four such half dilutions will have diluted the antifreeze by a factor of 16, at which time it's less dangerous. But there's still a significant amount of antifreeze, so you might be violating the law by flushing and letting the dilute spill. Not only that, but this method drains 2 to 3 gallons per dilution, meaning you'll need to take 8 to 12 gallons to the licensed disposal facility. That's lots of containers, and lots of stuff to carry.

Be sure to let the engine cool completely each time, or you'll be burned severely when you open the radiator cap and the radiator petcock.

Successive Half Dilution
PRO
• Safe for the engine
• Only the radiator petcock is touched

CON
• Takes a long time (cooling every dilution)
• Excessive materials to dispose of
• Spills significant amounts of antifreeze during later flush
• Risk of injury if done wrong

Single half-dilution
Some recommend simply draining the radiator once, refilling it with water, and then starting the flush procedure. Thus only the radiator's contents are brought to the licensed disposal facility. The antifreeze remaining in the engine is diluted during flush and spilled onto the driveway and down the street gutters to the storm drain. Although the flushing process greatly dilutes this antifreeze, it can still pose a grave danger for animals, it's not environmentally sound, and it's probably illegal in most locations.

Single Half Dilution
PRO

• Safe for the engine
• Only the radiator petcock is touched
• Very quick
• Very little material to dispose of

CON
• Illegal in most places
• Spills dangerous amounts of antifreeze during later flush
• Spilled antifreeze runs down the street and into the storm drain
o Any animal can drink it all along the way
• Risk of injury if done wrong

Running quick empty
I used to do this. It's risky. Basically, with the engine cold, open the radiator petcock into a large collection pan, start the engine, and turn on the heater full blast. The radiator drains while the system is still cool, and when the thermostat opens, the engine and heater are likewise drained into the radiator. If the radiator petcock can drain the coolant before the engine overheats, you're fine. Otherwise, you can cause an overheat and consequential damage.

As a practical matter, you'd want to watch the thermostat and shut down the engine when the temperature begins to head for the red. Better still, have one person watch the petcock and one watch the temperature gauge, and shut down when the draining stops, or when the engine begins to head for the red -- whichever comes first. If the drainage was not complete, you'll need to use the dilution techniques discussed previously.

To increase your chances of a total drain, you might want to disconnect the lower radiator hose. This allows coolant to drain very quickly, hopefully long before engine temperature becomes a problem. When removing the lower hose, try not to pry it off with a screwdriver, as that could damage the fitting on the radiator. If it won't twist off or pull off, perhaps you shouldn't remove this hose, unless you want to carefully cut it off with a knife, and then purchase a new lower hose.

Running quick empty
PRO

• Very quick
• All coolant drained and gathered without dilution
• Legal and environmentally sound

CON
• Risk of overheat and engine damage
• Risk of injury if done wrong

Running quick empty with thermostat removed
This is exactly like the normal running quick empty, except the lack of a thermostat means engine and heater coolant will circulate to the radiator while the engine is still cold, thereby reducing the risk of engine damage.

One problem is that some coolant will spill when the thermostat is removed. Unless that spilled coolant is caught in a pan, it's an environmental problem, a risk to pets and small children, and may be illegal.

One possibility is to start with a normal running quick empty, let the engine get cold, then remove the thermostat and do the second quick empty. The second quick empty occurs immediately instead of waiting for the engine to warm up. This lessens the risk of consequential damage to the water pump when it operates without liquid, and lessens the likelihood of overheat. To reduce it more, you might consider simply draining the radiator, closing the petcock, and running until hot (at which time much of the engine's coolant will have moved to the radiator. Because the thermostat is amongst the highest points of the cooling system, there's a good chance that it can be removed without significant spillage.

Running quick empty with thermostat removed
PRO

• Very quick
• All coolant drained and gathered without dilution
• Legal and environmentally sound
• Great reduction in likelihood of overheat

CON
• Removing thermostat is time consuming
• Slight risk of overheat and engine damage
• Increased possibility of coolant spill
• Risk of injury if done wrong

Simultaneous draining of radiator and engine
Most engines have one or more coolant drain plug to drain the engine itself. Theoretically, by opening all air bleeds, all engine drain plugs (remember to drain each into a pan), and the radiator cap and petcock (once again, drain into a pan), you can drain most of the system's coolant while the engine is cold and not running. This eliminates the risk of overheat and reduces the risk of personal injury. And assuming that you catch and turn in all the drained coolant, it's one of the most environmentally responsible methods.

But drain plug locations are specific to specific car makes and models, and they're usually very difficult to get to. If you strip, shear or break an engine drain plug, you're in a heap of trouble, son. And you should really replace the washers on those drain plugs -- and those parts might not be so easy to get. Before attempting this, be sure to obtain the manufacturer's documentation on coolant draining.

Simultaneous draining of radiator and engine
PRO

• All coolant drained and gathered without dilution
• Legal and environmentally sound if care is taken to avoid spillage when removing thermostat
• When done right, remores all risk of overheat
• Reduces risk of burns

CON
• Loosening and replacing engine drain plugs is difficult and time consuming
• Drain plug washers should be replaced
• Danger of damaging a drain plug, cross threading it, or not being able to get it back in.
• Greater risk of injury due to working under the vehicle
• Very difficult and time consuming

Install the flush kit
You can buy a flush kit to "wash out" your cooling system. As far as I know, the law says you must have already drained all your coolant, so that the only thing you're spilling is water. Check with your local authorities.

One way to flush the cooling system is to run it with the heater running full blast, the radiator petcock open and spilling on the ground (there's no more antifreeze left, remember), and a garden hose pouring in the radiator. Such a method would take a long time to do a good flush. A much more efficient flush method is to buy a flush kit. My local Discount Auto Parts store sells a Zerex flush kit for about $4.00.
The flush kit comes with the following parts:
• Back flow prevention coupler
• Flushing T
• Cap for flushing T
• Two hose clamps
• Deflector

According to the instructions, you start by installing the flushing T. Start with a cold engine. Cut the heater inlet hose in a convienient place at least a couple inches from hot engine parts. It's the hose between the firewall and the engine block, not the one between the firewall and the water pump. Remember, the system has been mostly drained, so very little coolant will spill. Slip a hose clamp over the hose on each side of the cut, then slip the hoses over each end of the flushing T. The kit comes with three different sized flushing T's to accommodate any sized heater hose. Make sure the vertical part of the T is pointed upward. Then tighten the hose clamps so that the flushing T is permanently and securely installed. Finally, screw the appropriate end of the back flow prevention coupler onto the T. The instructions will tell you which end is appropriate.

Last edited by dragginwagon406; 03-31-2007 at 02:47 AM..
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Unread 03-31-2007, 02:03 AM   #9
dragginwagon406
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Flush
One flushing method is running a garden hose into the radiator fill pipe of a running car with the radiator petcock open. This method isn't particularly efficient.

The other way is to use a flush kit. The preceding section discussed its installation. To flush using a flush kit, do the following on a car with a cold engine:
1. Screw a garden hose onto the back flow prevention coupler whose other end is connected to the flushing T
2. Make sure the radiator petcock is closed
3. Remove the radiator cap
4. Insert the deflector into the radiator fill pipe **
5. Turn the heater control onto the high position
6. Turn on the water to the garden hose
7. Start the car

** The deflector is made of a tough plastic. It snaps into the fill pipe with a tight pressure fit. I believe that with an old corroded metal radiator, or a radiator with a plastic fill pipe, it's conceivable that such a press fit could damage the fill pipe. The only function of the deflector is to move the spillage away from the car. You might decide it's better to let the water spill right out of the fill pipe.

Also, the deflector is too short to move the spilled water away from the car. If you use the deflector, you might want to tape a short length of hose to it in order to move the spillage entirely away from the engine compartment and car. Do not let the hose get anywhere near the fan, fanbelts, or other moving parts, or the result could be severe damage or injury.

WARNING!
If you connect the back flow connector in the wrong direction, or if the back flow connector malfunctions, or if you forget to remove the radiator cap, it is possible for the car's coolant to "back up" into the hose and into the water supply. This is an extreme sanitary breach, and if there are significant toxins in the cooling system (flushing solutions and antifreeze are both very toxic), people could be poisoned. Be VERY careful!

Run the car until the fluid coming out the radiator has been clear for five minutes. At that point your cooling system can be considered flushed and clean.

2nd Drain
Shut down the engine and wait for it to cool. It shouldn't be very hot because you've been moving cold water through and out of it. If you're using a flush kit, remove the back flow prevention coupler from the flushing T. Turn the heater on full hot. Remove the radiator cap and open the radiator petcock. let drain. Because you have all clean water in the system, there's no need to drain the engine.

Add Coolant
Close the petcock. If you're using the flush kit, leave the flush T open. Turn the heater to the full heat position. Open any bleeder valves that are reasonably easy to open.

Look up in your owners manual the amount of antifreeze (not coolant, but the amount of antifreeze necessary to fill the cooling system with 50/50 coolant (or whatever mixture you need to give freeze protection for your coldest days). If your owners manual lists only the cooling system's fluid capacity, divide that amount by 2 for the amount of antifreeze to make a 50/50 mixture. If, in order to protect against freezing in extremely cold weather, you need a 60/40 mixture (60% antifreeze), multiply the cooling system fluid capacity by 0.6.

Put that amount of pure antifreeze in your radiator. Then top off with distilled water. Make sure you add enough to bleed all air from the system. You should see some coolant come out the bleeder valves and/or flush T.
The reason you don't simply add 50/50 is that the engine contains 100% water, so you could never reach 50/50 by adding 50/50. Similar logic applies for any mixture percentage.

Close system
Close the bleeder valves. Put the cap on the flushing T. Install the radiator cap

Test
The big reason for testing is that air can get trapped in the system. Trapped air can cause overheats in two ways:
1. By creating a low coolant situation
2. By creating a bubble around the thermostat's heat sensor, so that the thermostat "thinks" the engine is cool and does not open.

Most of the trapped air comes out within minutes after running the car. Some comes out for a few days after. As the air comes out, it must be replaced by the desired mixture of coolant.

Run the car for several minutes, revving the motor every once in a while. Shut down instantly if the temperature starts heading for redline. Otherwise, let it run for 15 minutes and then shut down. Open the hood, and fill the reservoir to the "full, hot" mark with the proper mixture of coolant. Let the engine cool. Then open the radiator cap, and if the coolant isn't up to the top, top it off with the proper coolant mixture. Repeat until the cool engine doesn't require a top off.

Then, for the next few mornings, remove the radiator cap and verify that the coolant is up to the top, and if it isn't, top it off with the proper coolant mixture. Likewise, if the reservoir coolant level is below the "full, cold" level, top off the reservoir with the proper mixture.

Easier Coolant Maintenance Methods
Do the traditional methods seem to involve too much time, hassle, injury risk, and legal risk? How did you like the risk of accidentally backing up your coolant into the water supply if you accidentally build up pressure in the system and the back flow prevention coupler fails or is connected wrong? Might that involve some fines and lawsuits?
There are two easy methods for coolant maintenance. One's not as thorough as the traditional methods, and one is expensive and might not be as thorough. But they both lower the risks of damage, injury, environmental harm and legal liability to acceptable levels. When viewing the deficiencies of these methods, keep in mind that the traditional alternatives might be even less attractive. The two easy methods are:
• Frequent radiator drains
• Letting a professional do it

Frequent radiator drains
One interesting solution to the flushing problem is to replace quality with quantity when it comes to coolant replacement. Instead of replacing every drop of coolent every year or two, replace half the coolant every 6 months. This can be done by draining and refilling the radiator, without the hassle of draining the engine. When done this way, you can consider the 6 months between the radiator drain/replacements as a long "flush" period. This solution is quick and cheap.

Start with the engine cold, and open radiator cap and then the radiator petcock and drain the radiator into a pan for disposal at the disposal facility. Also, find a way to drain the reservoir into that same disposal pan. Add a gallon of water to the radiator with a garden hose, and catch what comes out the petcock in the pan That should remove most of the remaining ounces of coolant.

Unless you're extremely environmentally responsible, you can then rinse the radiator and reservoir with a garden hose. After all, probably there are only a few drops of coolant left in the radiator, and you're diluting that coolant 100 to 1, so risk to animals and the environment is minimal. Once again, allow the radiator to drain completely, and then close the petcock. Now fill the radiator with the proper antifreeze/water combination for your climate, squeezing the hoses to try to free air bubbles.
If all went well you didn't introduce air pockets into your cooling system. But sometimes air pockets happen. Too much air can cause overheats, either through a low coolant condition, or by an air bubble surrounding the thermostat's temperature sensor.

Fill the reservoir to the "full, cool" line with the proper mixture for your climate. Place a closed bottle of that mixture in your trunk for use while testing. Now start the engine and drive it around the block a few times, keeping a VERY careful eye on the temperature gauge. If it starts to move toward the redline, shut it down immediately. Otherwise, after about 10 minutes pull back into your driveway. Either way, with the engine hot, top off the reservoir to the "fill hot" line with the proper mixture. When the car is cold again, note the reservoir level. If it's below the "full, cool" level, repeat the instructions in this paragraph.

Every day for a week, when you get up in the morning, before starting the car open the cold radiator and top off with the proper coolant mixture if necessary, and top off the reservoir to the "full, cool" line. This is replacement of air that got burped out during yesterday's driving. During the first week watch the temperature gauge very carefully. If you have no gauge (only an idiot lite), try not to go on long drives for the first week, and check the reservoir level every time you come out to the car.

For even better accuracy, before refilling with coolant, measure the coolant mixture with a hydrometer (assuming you've always used ethylene glycol), and when calculating the replacement mixture, make sure to compensate for any excess in the existing mixture.

This method takes maybe 15 minutes (not counting around the block testing or the trip to the licensed disposal facility), it's performed almost entirely on a cold engine, it's cheap (typically a gallon or 1.5 gallons of antifreeze), it's environmentally sound because it's trivially easy to catch all the coolant.
Each time you perform this procedure you replace roughly half the coolant, and as a simplification you can assume you're removing 1/2 of the coolant's disolved impurities. If you do this procedure twice a year (that's about $20.00 and a half hour of your time plus time spent testing and at the disposal facility), you've replaced 75% of your coolant every year, and every 2 years you've replaced 93.75% of your coolant. This isn't as good doing a 100% replacement and backflush every 2 years, but if you continually refill the radiator every 6 months it's probably good enough to keep your cooling system healthy for a very long time. And remember, without knowing exactly what an auto shop does, it's very possible that this procedure is actually more thorough than what the shop does.
A huge advantage of frequent radiator drains is that you control the water being used. By using only distilled water, you cut way down on the likelihood of calcium-caused deposits. Even if your system started with tap water, within 4 changes you've replaced 93.75% of the old tap water with distilled water.

Frequent radiator drains
PRO

• Legal and environmentally sound if you're reasonably careful not to spill.
• Extremely fast and easy
• When done right, removes all risk of overheat
• Reduces risk of burns
• You know exactly what went into the system
• You can use distilled water

CON
• Not as thorough as a flush
• May not reduce heavy deposits in a previously undermaintained car
• Must be done every 6 months

Letting a professional do it
Perhaps the easiest solution is to let a professional clean, flush and replace the coolant. You need to ascertain that the professional will really remove all (well, 99%) of the old coolant, flush the system with water, drain the flushed water, and then replace with brand new coolant. Some professionals merely drain the and rinse the radiator, and then refill with the correct solution. You could easily do that yourself -- it's not what you're paying them to do.

Be sure the professional uses the correct antifreeze for the car. Some shops don't take the time to look up recommendations. And ask whether the shop is using recycled antifreeze. Recycled antifreeze is made from old antifreeze and contaminants -- many from cars much dirtier than yours. The quality of recycled antifreeze is dependent on the ability of the recycling machine to filter out whatever bizarre contaminants were present in the raw material, and upon the corrosion inhibitor which the shop adds. With new antifreeze priced at $6.99 a gallon (add a couple bucks for the shop's markup), recycled antifreeze might not be worth it.

Letting a professional do it
PRO
• Effortless and not time consuming
• You are not responsible for coolant disposal or any environmental or liability problems.

CON
• Costs money
• Requires being without your car for hours or days
• You need to research how the professional does the job. For instance, some professionals simply drain the radiator and pour in coolant. You could have done that yourself in less time than it takes to drive to the shop.

Last edited by dragginwagon406; 03-31-2007 at 02:54 AM..
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