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Unread 07-24-2012, 07:19 PM   #1
ttrevino
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XJ overheating when stopping

When I first bought this XJ, I opened the radiator cap and overflow reservoir and it looked all sluggy, so I flushed it with water, ran the heater for a bit, running water from the top, letting it flow out the drain cap at the bottom of the radiator, closed the drain, filled it with water, let it cool, and replaced the fluiability about 70/30. A couple of weeks later, my lower hose blew a hole while I was out, so I bought some repair tape, filled it back with fluid and water, and made it home, about an hours drive. As soon as I turned off the truck, the lower hose blew out past the tape, but at least I made it home. I bought a new hose, new fluids, and thought I'd replace the thermostat at the same time. Today I drove about 2 hours, and when I stopped, the temp gauge pegged to red and I could hear bubbling under the hood, but it didn't lose any fluid. I ran the heater, which dropped the temp back to normal, then shut it off while I went to the ear doc, but had to drive another hour to my next destination, and when I stopped there, it heated up again, but not as bad.
My question is when I replaced the thermostat, I used a 195 degree unit, but noticed the PO had a 160 unit installed. Normally the XJ runs around 210-215 but not higher. Should I have replaced the thermostat with another (or the same) 160? I'm concerned that it's going to keep overheating and maybe there's another problem that I'm not seeing?

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Unread 07-24-2012, 07:27 PM   #2
YoureverydayXJ
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You'd probably be better off matching your old t-stat, since that's when it went awry. Also, test your radiator cap. If its not tight, or is faulty you'd definitely overheat like that.
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Unread 07-24-2012, 07:40 PM   #3
donthelegend
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Did you run your XJ between replacing parts and driving the two hours? When you open the system up to work on it, air gets in and it takes a few hot/cold cycles to get it all out. While there is air in the system, higher than normal temps and hot spots can occur. I usually try to cycle the sytem a few times after working on it before driving it any long distances, this helps get most of the air out.

What is the condition of the rest of your cooling system? Water pump, upper radiator hose, heater hoses, fan clutch, radiator cap, radiator? The entire cooling system needs to be in good condition to work properly and any single part can cause a major problem in the operation of the entire system.

The fact that you removed a 160 thermostat would suggest the the PO had overheating issues he was trying to cover up, and now you are dealing with them. I would suggest an overhaul of the entire cooling system (all hoses that you haven't replaced, fan clutch, radiator cap, water pump). Be prepared to replace the radiator as well, you may be able to leave it alone, but its not uncommon for a side tank to fail after replacing the rest of the system because it hasn't had to hold proper pressures until new parts are installed, and the plastic has fatigued to the point of failure.
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Unread 07-24-2012, 07:44 PM   #4
CJ7-Tim
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Overheating can be caused by anything that decreases the cooling system’s ability to absorb, transport, and dissipate heat, such as a low coolant level, loss of coolant (through internal or external leaks), poor heat conductivity inside the engine because of accumulated mineral deposits in the water jackets or radiator, a defective thermostat that doesn’t open, poor airflow through the radiator, a slipping fan clutch, an inoperative electric cooling fan, a collapsed lower radiator hose, an eroded or loose water pump impeller or even a defective radiator cap.

The cooling system is a group of related parts that depend on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under-performing or suspected weak parts. Any component part of the cooling system that is not fully doing its job will stress the others and your cooling system will overheat. The most important maintenance item is to flush and refill the coolant periodically. Coolant should be replaced every 36,000 miles or every three years. Anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system, but they have a limited life span. The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat.


-Use a flushing/cleaning solution and then drain and fill the radiator with a fresh 50/50 coolant and water mix. With a neglected cooling system you may have to flush several times.
-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside. Clean or replace as needed.
-Replace the thermostat with a STANT or Robertshaw 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap if your Jeep has one. An old worn out cap will allow boil overs and/or allow the coolant flash over into to steam. You will see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.
-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that “looks” OK is not the same as working OK.
-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.

If you have covered all the points listed above and still have overheating issues, inspect the head for cracks and head gasket for leaks. Exhaust gasses entering the coolant can raise the temperature of the coolant or cause steam pockets in the coolant that will temporarily block the flow of coolant

Read more about cooling systems here –

www.offroaders.com/tech/engine-overheating.htm

www.familycar.com/classroom/coolingsystem.htm
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Unread 07-24-2012, 08:14 PM   #5
ttrevino
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Definitely a lot to check out. Thanks for the quick responses!
But in short, the lower hose doesn't have the wire insert as it didn't come with it from O'Reilly's. Should I have added the old one? I bought the "fail open" 195 thermostat, about $12, instead of the econo that was $3.99. I don't see the temps jumping back and forth, just overheating without steaming or losing coolant. when I did the initial flush, I ran a hose into the radiator, opened the drain valve, and ran the truck on that water until it ran clear water out of the drain, including running the heater.
I didn't run the truck except around the neighborhood for about 10 minutes, before making the 2 hour drive. All the other parts seem to be in working order, upper hose looks good, heater hoses and pump aren't leaking but I don't know what they look like inside. I do think the PO was trying to "rig" something rather than fix the problem, as I found that out when working on the throttle body and he added a nut under the throttle linkage to idle the truck up, instead of cleaning the TB and replacing the TPS.
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Unread 07-24-2012, 08:32 PM   #6
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One might reasonably assume that the cooling system has been neglected for a long time, and that it needs some TLC and parts replacement. Overheating tends to prove this point. Looking good, and actually being good, are not the same thing.
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Unread 07-24-2012, 08:51 PM   #7
ttrevino
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Very true. When I pulled the thermostat housing, I did look inside the upper hose and heater hose and could see a little sludge in there, but not 'too' bad. I'll start with the simple stuff first like the radiator cap, etc. The upper hose felt flexible and supple, so I didn't think it needed replacing.
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Unread 07-25-2012, 12:38 PM   #8
ttrevino
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I replaced the radiator cap just now, drove 11 miles to work, stopped at a light, and the "check gauges" light came on, and the needle pegged to the hot side. I stopped in a parking lot, ran the heater a couple of minutes, and it cooled down enough to get off the high end. I'm not losing fluid bubbling over, but did notice there's a small leak at the thermostat housing from either the upper radiator hose, or the housing itself, but I couldn't tell which since it was too hot. I listened and didn't hear the 'bubbling' sound that I have been hearing though...?
I checked the truck after letting it sit for about 10 minutes, and ran it for a few. The thermostat housing read 226, and with the truck running for those few minutes, I never saw the extra cooling fan start up. I'm assuming this should kick on when needed, at a certain degrees? This might be my whole problem, if I'm lucky!
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Unread 07-26-2012, 07:21 PM   #9
YoureverydayXJ
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If the lower hose collapses (needs spring) it would basically seal off coolant flow to the radiator. If there's a definite leak, you are building minimal to no pressure and drastically reducing the boiling point of your coolant. http://www.engineeringtoolbox.com/bo...ter-d_926.html
If your fan doesn't work, you can guess. You can test by turning on the AC at running temp. It should run every time the compressor is on.
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Unread 07-27-2012, 07:57 AM   #10
ttrevino
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Definitely not coming on with A/C on, I live in Texas, we run the A/C even in the 'winter'!

I swapped out some relays and fuses, and all those seem good, but I haven't tried wiring the fan directly to 12v yet, will try that this afternoon. It might be the fan is dead and needs to be replaced. The strange thing is yesterday it was pretty warm, and I drove the truck home, parked in the driveway and waited about 10 minutes for the gauge to peg to the right, but it never did. I was actually trying to overheat it, so I could confirm that the fan wasn't coming on over a certain temp but it never went over the line past 210 (220?) Strange. I'm not saying it's healed itself, but definitely want to make sure it doesn't happen again and leave me stranded somewhere. Thanks for the advice on the lower hose spring, I tossed the other one, so I'm not sure where I can buy just the inner spring? Any suggestions?
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Unread 08-13-2012, 06:26 PM   #11
ttrevino
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I replaced the cooling fan and problem solved! Thanks everyone for the advice!
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