overheating problem.

[Rufio]

just recently my jeep temp gets really high while sitting at idle, but when i start driving the temp drops to the norm. is this cause of a shot water pump or could it be beacause the thermostat any help?

[Rufio]

anyone?

[RichP]

Fan clutch, typical sympton.

[Rufio]

my fan is still rotating though....?

[BillyBob]

loose serpentine belt?

[Rufio]

serpentine belt is nice and snug

[Tim96XJ]

I would check the radiator :repair: . This happens alot when they start to get cloged. Its what happened to mine. Also yes it could be the t-stat. Easiest to replace and cheepest to.


Not to be a smarta$$ but the coolant is full and there are no leaks you can see.

[Ridr]

my fan is still rotating though....?
that doesn't mean it is rotating with any force behind it, even with the clutch out the fan will spin , just not near as fast as it should
run the jeep up to normal heat range , shut it off and pop the hood. turn the fan by hand , you should feel strong resistance

[94_2wdcherokee]

I just had the same problem with my jeep and i changed out the Thermostat and it runs like a champ now! It was a real easy task.

[reddragon72]

I just had the same problem with my jeep and i changed out the Thermostat and it runs like a champ now! It was a real easy task.


I run no thermo in Houston, works alot better that way. My temps are easier to control when with it out, move just a tad and it is good to go. My radiator is starting to loose it tho, keeps killing water pumps with to much back pressure.

[RichP]

A normal healthy fan clutch tends to 'roar' when it starts up cold then gets quieter after about 30seconds to a minute. Not a scientific method just an observation.

[Gojeep]

I run no thermo in Houston, works alot better that way. My temps are easier to control when with it out, move just a tad and it is good to go. My radiator is starting to loose it tho, keeps killing water pumps with to much back pressure.

I doesn't matter where you live but that is not a good thing to do. It will still take longer to reach the 'correct' operational temp where 90% of all your engine wear takes place getting there if at all in your case. You have 4x as much wear at 160* than 180 for instance. Not to mention that your ECU will stay in open loop mode meaning you will be running a rich mixture so using more fuel and have less power. There is not a person in the world that recommends running without a thermostat that knows about cooling and how critical they are to a cooling system.

[jeeperjohn]

If you have too much back pressure you have: a clogged radiator, or a radiator cap with too high a pressure rating, or an obstruction of some kind in the cooling system. Oh yeah, or a bad head gasket.

[jeepsrock]

how high is really high ? how close to the red does it get .

pete

[ROADLESS]

The XJ forum at Jeeps Unlimited has a good sticky regarding this. Just click here http://www.jeepsunlimited.com/forums/

[reddragon72]

I do know that some of the long running offroad vehicles have ben known to run electric water pumps so while the engine is off the water will circulate and the cooling fans will cool the radiator to get the temps back down low so the engine will run faster. To my understading from several mechanics the thermostat really just gives hot water for the heater core, and many run without them during high heat months especially off roaders where slow speeds can really cause temps to soar, but keeping the water flowing consitantly allows for way better running. I'm not sure, but I have been running without one for over a year and have had no ill effects, still getting the crappy 4.0's 17MPG and still darts from a light like a lighning bolt even with 31" mudders on there, so I'm not sold on "it's better to run with one" They even sell lower ranged thermos to keep the car cooler, as everyone knows heat kills your engine not cold.

[Dr. Dyno]

just recently my jeep temp gets really high while sitting at idle, but when i start driving the temp drops to the norm...

What is happening is that your fans are not pulling enough air through the radiator when the engine's idling. When you drive off, you get enough "ram airflow" through the radiator to keep the engine cool and that's why the engine can run happily without a fan at all above 30mph.
Since you have two fans, at least one of them isn't working properly. The viscous clutch fan tightens up as the engine warms up so by the time the engine's hot, the clutch fan can rotate at up to a maximum of ~2000rpm. If the viscous clutch is shot, the fan just "freewheels" at a lower speed and doesn't pull in much air. Spin the fan by hand when the engine's hot (ignition off) and see how much resistance there is.
The electric fan should switch on when the temp. gauge moves to about 5/8 (220*F). If the gauge goes beyond that and the fan still doesn't come on, see if it works when you switch on the A/C. If it does, that means the sensor in the t'stat housing (HO engine) is at fault. If it doesn't the problem's either a blown fan relay, faulty wiring to the fan motor, or a burnt out fan motor. You can "hotwire" the fan motor directly to the battery to see if it works if you find yourself in this situation.

[5-90]

If you want to check your fan clutch; let the engine warm up, turn it off, and try to spin the fan by hand. It should go, but there should also be a definite "drag" when it does.

The thermal fan clutch/viscous coupling used on most mechanical fans is not a perfect device - I'm sure there's some slip, even when it's new and locked up. You can replace the thing (which you should do if it's more than a couple years old - my typical fan clutch life seems to be about three or four years,) or just "pin" it for a permanent, 1:1 coupling. The catch to that is that it will take a little longer to warm up.

As far as no thermostat - I've got my 88 that I run without one. No matter what else I do, it always wants to overheat with a thermostat in place (yes, I know how to bleed air out of the system, and I do flush regularly.) I've noted that this is just a fluky thing that happens - sometimes, perhaps once in a thousand or so, you'll get an engine that just doesn't like having one. Once I decided to remove the thing, no ill effects, and no overheating. Go figure... I don't recommend it for general use, but if your engine doesn't like having one, don't bother.

5-90

[Rufio]

ok i will check my fan clutch, but this just happend recently when i was out 4wheelin. it was fine tell i got out there did some light wheelin through water and mud then i idle'd and it started overheating

lol i even got a pic of it....

http://memimage.cardomain.net/member_images/6/web/2286000-2286999/2286156_3_full.jpg

[Pharaoh XJ]

can somebody tell me how to bleed air cause i have the same problem???

[5-90]

What year?

5-90

[RichP]

ok i will check my fan clutch, but this just happend recently when i was out 4wheelin. it was fine tell i got out there did some light wheelin through water and mud then i idle'd and it started overheating

lol i even got a pic of it....

http://memimage.cardomain.net/member_images/6/web/2286000-2286999/2286156_3_full.jpg


Clean the mud out of and between your radiator and condenser then see what happens.
As far as whether it is good or not, there is a method that involves drilling a small hole between the fan and the radiator then sticking a thermometer in there, watching it heat up, then block the radiator and whatch it get hotter, remove block and see it cool down. That the FSM method, the one I use is start it cold, the fan should ROAR for about 30 seconds then quiet down. Every bad one I've found did not ROAR when it was cold.

[DubaiXJ]

I There is not a person in the world that recommends running without a thermostat that knows about cooling and how critical they are to a cooling system.

True story.

[5-90]

True story.

Normally, I'd agree with you. Swing wrenches for somewhere around 30 years...

I've run across three engines total that DID NOT LIKE having thermostats installed, and ran better without them - all that I've owned, oddly enough. They were...

1980 Honda Accord 1.8L I4 CVCC
1985 Chevvy Cavalier 2.0L I4
1988 Jeep Cherokee 4.0L I6

I'm still not sure why, but they would not fail to overheat within the space of 30 minutes with a thermostat - with all the rest of the cooling system either new or just flushed (for the engine and heater core.) I know they were clean.

My 88 still don't like having a thermostat - and I just can't figure out why. I know it's maintained well - I do it myself. But, out of the probably couple hundred engines I've dealt with - in all sorts of vehicles and equipment - those are the only three I've run across that just didn't like thermostats. Go figure. One thing I do know - they're thoroughly individual examples. Maybe when I rebuild the engine in my 88 I can inspect it more thoroughly, and see what the issue it. I didn't have a chance to do so on the other two.

5-90