Cherokee overheating problems

My 90 Cherokee has a problem overheating. i can drive it a couple miles when it has been sitting overnight. the temp just keeps on going past 210. could my thermostat be not working? any help would be great.atriot:

I have found Jeeps to be very finicky about the cooling system. They heat up fast, and if one component is not operating properly they overheat in a hurry!!

Could be lots of things.......just a few examples...

Radiator flow blocked

Soft radiator hoses collapsing

Thermostat bad/sticking

Sometimes, the water pump "vanes" could be eaten away due to corrosion over the years.

If you don't have any leaks, I would start by draining and flushing the cooling system....just make sure you don't leave air in the system. If the radiator flow is good, make sure your electric fan is working....it should come on about 210 or so and any time you have the A/C on. Good time to check the hoses and replace the thermostat as well.

You didn't state whether this was highway or city driving if on the highway its usually a flow problem and if in town its likely a fan problem.

I just went through the cooling system on a 96, changed the water pump, lower radiator hose, thermostat and fan clutch. In total, parts were less then $100.

Give us more info on the state of your cooling system (if known) and what situation (speeds/time of driving) the overheating occurs.

Dad had this problem with his '90 Larado, he swapped out a whole bunch of parts but the only one that actually made a difference was the water pump. Now that truck won't even hit 190* in most situations even with 281k on the clock.

jk333 said:

My 90 Cherokee has a problem overheating. i can drive it a couple miles when it has been sitting overnight. the temp just keeps on going past 210. could my thermostat be not working? any help would be great.atriot:

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As has been mentioned, it could be one of several things or maybe a combination of issues. How far past 210 has it gotten? Is this when running the A/C or does it happen regardless of whether the A/C is on or not?

If it really is continuing right on past 210 with no limit in sight, I would start with the thermostat. Chances are very good that it is sticking in the closed position not allowing coolant to reach the radiator. Buy OEM only for the thermostat. I went through 3 thermostats from my local Checker and Napa before I spent the extra 5.00 for an OEM one which finally cured my overheating problem.

BTW, if you determine that the problem lies with the radiator, research replacement options. Some say the three row core radiators are the way to go and others claim they offer poorer cooling than a stock radiator. Summit racing has affordable aluminum radiators if you don't mind buying a universal fit style and making it work, but I can't really say how well they cool since I haven't bought one myself.

If the temp on your jeep just keeps climbing and never pauses around 200-210, it is almost certainly your tstat, like Israel said. The other possibility is a hosed water pump, although not as likely. Both have happened to me. One time I had a water pump go out without any warning at all, no sound, leaks, or anything. I also had a bad tstat that wouldn't open until about 230 or so, so the temp would quickly reach 230, then zoom back down to about 200 in about 5 seconds when it finally opened; not good.

If the problem just started happening, it likely isn't your radiator. Radiators in my experience don't just suddenly fail (unless they spring a leak), they just gradually lose effectiveness. I suppose with the Renix you could have a faulty pressure bottle, but that probably wouldn't show itself it the symptoms you have described.

It isn't hard at all to change the stat, I don't know about the Renix but my 94 just has 2 bolts that hold the tstat housing on, pop it off, remove gasket and tstat, put new one in, apply gasket maker to new gasket and bolt it back on. Not hard. I've seen shops actually charge anywhere from $40-70 (70!!:huh. It took me 15 minutes the first time, 10 minutes now.

And get an OEM tstat!! They only cost 10 bucks or so and come with the gasket. Trust me when I say I've learned it makes no sense to use a lower temp stat or a cheaper non dealership tstat. Also, if the problem lies with your waterpump there is absolutely no reason to spend over $100 on a Flowkooler or some other "high-performance" one. An OEM style replacement is more than adequate. I have a stock or OEM replacement tstat, waterpump, hoses, and rad cap. The only "upgrade" in my system is a 3 row all metal radiator and my jeep always runs at 210. (I should add basic oem replacment fan clutch as well)

the driving was on highway and around town. ill tell you that when we were on the highway, the temp seemed to drop barely and we were blasting the heater the whole time. it did get hotter in around town driving. the temp did go right on up into the redzone. but i had to shut it off. and wait for it to cool down to limp it home. i think its the thermostat sticking. if memory serves me correctly, its the factory thermostat, (rig has about 150K) ill try replacing the thermostat and see what happens from there. thanks to all you guys for helping out with the overheating problem.

jk333, your last post sheds a bit of a different light on the situation. Now by all means, at 150K I would still be willing to bet that the tstat is the culprit of your problem, but it seems as though you're saying you noticed the temp dip slightly when you sped up? When you're on the highway and your tstat is stuck closed, it will only start heating up faster because your engine is working harder; it almost certainly won't show any sign of cooling down even in the slightest if your tstat is truly stuck shut.

With that in mind, it is difficult to know exactly how your gauge is reading when we on this forum can't drive it ourselves. It still sounds like a tstat, and no matter what you should replace it, even if it gets up into the 230-240 range one time a good tstat can be ruined.

But it could also be a w/p (especially if the original is still in there with 150k). If the impellers are rotten, they do very little to circulate coolant, especially at a low rpm. On the highway they may have enough speed to circulate a bit of coolant, which could slow the overheating process a bit. Again, this isn't likely to just suddenly happen, but I don't know how long you've been experiencing this issue, if it just occurred or has gradually been getting worse. Like I said before, I actually did have a waterpump spontaneously stop working without any sounds, leaks, nothing... weird.

My original w/p lasted about 110K, tstat about 112K (coincided with a overheat from a bad w/p...), upper hose around 70K, Lower still good at 140K but just replaced both at 145K along with new radiator. Original radiator started to get worse around 135K, replaced 145K.

While your replacing the t-stat, check the auxiliary electric fan to see that it turns on w/the a/c. Also spin the clutch fan after it warms up - engine off - and see that it's a lot stiffer than cold.

I installed the 3 core radiator, all brass, and it would still overheat in stop and go postal delivery if the electric fan didn't kick in. Once over 25mph, air flow alone was sufficient. The radiator dropped the average temp 15+ degrees, so it's worth it to me. If your stock radiator is that old, even a flush won't restore flow capacity, which is why lower hoses suck shut. At that point a new radiator is all that will do, and the industry recommends at least one core more to compensate for the clogged up engine.

I've run my '90 converted to the open system, and it sure it easier to fill and burp.

Yeah, I agree with TiRod... do check the operation of your aux and clutch fan. However, I guarantee you that even if they aren't working they aren't the source of your immediate problem. Even if both fans don't work at all (obviously the clutch fan will always spin a little, even if the clutch is completely shot) it would still take a long time to overheat unless you were completely still. On the highway the fans make little if any difference because of the forced air cooling.

By the way, if the a/c isn't on, the electric fan should come on by itself when the temp gauge reads about 220 degrees and shut off once the temp gets back down to 200; you can verify this by letting it idle for a long time with the a/c off. This shouldn't happen very often, unless you are sitting in traffic in very hot weather with the air off, or idling along a trail at a half mph; or if your tstat is stuck shut it will happen quickly!

I have a 90 laredo that was overheating i changed thermostats, hoses, resevoir ect.. finally wound up changing the water pump with one i have on a 93 HO engine & fixed the overheating