You all have helped remind me why forum writing is so fun.
After reading all the responses I am a little taken back.
First, let me say I am a fan of KISS (keep it stock stupid). I don't agree in the idea of “upgrading” for the sake of upgrading specifically when it comes to engine, transmission and driveline components. You can put all the bling you want on your ride, those are personal preferences. When it comes to modifying the reliability of your vehicle I always caution against. The majority of people don't understand the principles of how a vehicle works in the first place, let alone how that modification will “add” to its reliability.
Let me talk directly to a couple of the points brought out in the responses:
the conception my Jeep is supposed to heat up 210 and stay there.
I have to call you on that. Reality being I have a 195° thermostat. A thermostat is a regulation not a moderation device. In a properly operating cooling system the thermostat will open at 195° allowing the cooled water from the radiator to mix with the warm water in the water jacket of the block. If the system is working correctly the temperature of the water in the water jacket would not exceed 195°. If the water is consistently 210° the 195° thermostat has no effect. By practical definition the vehicle is overheating.
I have to call you on that. The conception is the stock cooling system is more than adequate:
the reality being Chrysler Corporation has acknowledged it has cooling system problems as outlined in their technical service bulletin:
Technical Service Bulletin, OEM 7 Blade Fan-HD Fan Clutch
2001 Jeep Truck Wrangler L6-242 4.0L VIN S SFI
Temperature/Check Gauges Light ON
Engine - High Temperature/Check Gauges Light ON
NUMBER: 07-004-01 REV A
DATE: Dec. 14, 2001
THIS BULLETIN SUPERCEDES TECHNICAL SERVICE BULLETIN 07-004-01, DATED JULY 20, 2001.
High Engine Temperatures Due To Extended In-Gear Idling In Hot Ambient Temperatures
So let’s go ahead and put that rabid dog down now. Making an absolute statement is absolutely foolish.
The generalized assumption made here is I'm looking for cooling while off-road in a rock crawling:
the reality being I do very little rock crawling or off-roading. My issue is sitting on the capital Beltway at 4:30 in the afternoon not moving. Assumption is the deadliest enemy of all. Never ever come to a conclusion without challenging all of your facts.
Let me quickly go over the operation of an internal combustion liquid cooled engine and how temperature is regulated. In a four stroke engine during one cycle of the piston there is a fuel vapor explosion. The average temperature of that explosion is 1700°F. That temperature quickly heats the cylinder wall. For the next three strokes you have exhaust intake and compression which helped to cool the cylinder somewhat. There is an immediate need to transfer that heat away from the cylinder. So engineers built what's referred to as the water jacket surrounding the cylinder. We fill that water jacket with a “heat transfer fluid” the most abundant and cheapest of which is water. Don't be confused water is not the coolant; water is the heat transfer agent. Air is the coolant. The water serves a secondary function of heat moderator. In other words it helps slow the rapid heating of the cylinder and conversely helps to slow the cooling of the cylinder when the internal combustion stops. This allows the metal to expand and contract at a more consistent rate reducing the chances of cracking.
Now we need to regulate how cool water is brought in and hot water is removed. We do that with the thermostat. As you know thermostats come in varying temperature ranges that control their opening and closing. We cycle the heat transfer fluid out of the water jacket in into the radiator. The radiator function is to be a heat sink as well as a storage tank to increase the capacity of the heat transfer fluid. The radiator was not designed to be a convection style heat dispensation unit. In other words it has not been designed as a passive heat sink. It is designed to have forced air moving through it. Contrary to what you might think the forced air is the vehicle moving in a forward direction at a sustained rate of speed. When the vehicle is sitting still, obviously there is no air movement.
Enter the need of the fan. Any fan on a vehicle regardless if it’s electrical or mechanical is a parasitic drain on the engine. The fan by design is not adequate enough to move the appropriate amount of air through the radiator with the engine under load. The fan is designed to move enough air through the radiator to dispensat heat while the engine is in a no-load condition. As most of us know there are fans the bolt directly to the water pump pulley turning one-for-one with water pump pulley speed. Of course this hampers engine performance. To overcome those issues introduce the hydraulic fan clutch.
The fan clutch is a hydraulically operated unit that consists of a bimetallic spring, a valve and some hydraulic fluid. The bimetallic spring sets on the front of the fan clutch and reacts to the temperature between the radiator and the spring. As the temperature between the radiator and the spring increases the spring deforms and opens a valve inside of the fan clutch allowing the hydraulic fluid to engage the fan clutch. As the temperature cools the valve closes and the fan clutch disengages. The bimetallic spring moderates the temperature between the radiator and a fan clutch. The standard Jeep Wrangler fan clutch starts to engage 165° ambient temperature between the radiator and the bimetallic spring. Typically it starts to disengage a 180° ambient temperature between the radiator and a bimetallic spring. That's cooling system 101. There's a lot more science that goes in to an automotive cooling system but what I just described is the operation of the cooling system.
Let's talk about the fan clutch for a minute. The standard fan clutch while we use the word disengaged is not completely disengaged. All fan clutches regardless of their designation typically turn 20 to 30% of the time while they are in the disengaged state. While that's nice to know what you need to know is engagement. The standard fan clutch when engaged only turns the fan 60 to 70% of the rotational speed of the pulley. In other words it's not a one-for-one rotation. When you move up to a heavy-duty fan clutch the rotational speed increases to 80 to 90% of the rotation of the pulley. How much do you need is really dependent upon your application. How much air do you need moving through the radiator at no or low vehicle speed? There is a secondary consideration for standard versus heavy-duty or severe duty fan clutch and that his blade pitch in other words how much the blade is angled. Standard fan clutches typically are for a 1 1/2 inch blade pitch. Heavy-duty and severe duties are typically for a 2 1/2 inch blade pitch.
Now let's talk about application. If you're a rock crawler or off roading and your speed is typically 0 to 15 miles an hour that would mean:
- low forced air rates through the radiator
- constant fan clutch lockup
- accelerated fan clutch wear
if you are a road warrior and your speeds are typically in excess of 30 miles an hour what would that mean:
- hi forced air rates to the radiator
- consistent fan clutch disengagement
- diminished fan clutch wear
That's not my opinion it's just the physics of the way the system works. From all the replies the one that spiked my interest was the one about the fan clutch wearing out. When I read that response the author states; cooling was increased between 1500 and 3000 RPMs but the fan clutch was fully engaged. I can totally understand that the reciprocal being your engine was under a load at 3000 RPMs but wasn't moving fast enough to force air through radiator. In other words rock crawling or four-wheel driving. Makes all the sense in the world.
But I am a curious type. One post stated initially there had been something wrong with my radiator suggesting it was plugged or crimped. Had to think about that one for a minute. I had to think about it so much I went out and put the old five blade fan back on. In the ambient air temperature of 60° I went back to idling at 210. Put the nine blade fan back on, idling at 195 Test proof conclusive not enough air moving through the radiator.