Overheating... STILL

Alright, so ever since I bought my jeep a few years ago, my cooling system has always been a nightmare.

Things I have replaced:
-Radiator (4 times). Aluminum one in there now
-Thermostat / Thermostat Housing (High Flow From TurboCity, 180*f)
-Water pump - OEM
-Radiator Hoses - OEM
-Flushed the system multiple times
-Hood is lifted in the rear for a little bit of vent (not much)
-Mechanical fan clutch replaced with a new one
-Electrical fan is wired in via switch (also starts up fine w/o the switch)


It only happens when I leave the area and go camping. I wouldn't say it's dependent on altitude, but it could be. This past trip it seemed that if the Jeep was running over 2k rpm, that it couldn't keep it cool. It never got into the Red, but it got pretty close and I pulled over to let it cool down. It does this mostly at highway speeds, never even gets close while off-roading.

At one point it started smoking a lot, and it was transmission fluid, let it cool down for about 15 minutes then went on, and never had that problem again.

So I am trying to figure it out what is wrong with it. The only thing I can think of is maybe the thermostat is stuck partially open / closed? My friend thinks it may be the head gasket, but that's only a guess on his part. So I am thinking about replacing the thermostat and putting some vents on the hood and going camping again and see if that helps at all.

I have checked the oil before, but never noticed anything wrong with the oil (like there was anti-freeze in it), so that's why I doubt it's the head gasket, is there anyway to know for sure it isn't? He made it sound like the headgasket is compressed too much and is possibly causing detonation...

Oh and the jeep has 170k miles, 33" tires 4.10 gears...

If its cooling while not at speed it usually means a flow problem. Check the lower radiator hose. There should be a spring in the hose to keep it from collapsing. If the spring is not there the hose can callapse and block flow.
I have had the best luck with Robert Shaw thermostats. Did you replace the tranny fluid after it bioled over? if not you definately need to do that.

Check the fans. You may need a new clutch fan and I put a 10 blade electric fan from a 98 or newer on in place of my 6 blade. I don't know what to tell you on checking them but it looks like your not afraid of changing parts so I would change the fan and fan clutch too.

...and what year is it?

I didn't see a fan clutch in your list of replacements. That'd be my first guess.

Also, put the 195 T-stat back in. It's supposed to be a 195 and changing it to 180 will not limit the high end of the temp. A lower t-stat will just open sooner. Won't help with overheating. Does the radiator leak? Why so many change-outs.

I would tend to doubt the head gasket being the culprit as it would be an issue ALL the time, you'd be pushing coolant, or oil.

squirrel80 said:

Check the fans. You may need a new clutch fan and I put a 10 blade electric fan from a 98 or newer on in place of my 6 blade. I don't know what to tell you on checking them but it looks like your not afraid of changing parts so I would change the fan and fan clutch too.

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Forgot to include I also replaced the clutch on the mechanical one, though I am reading about the ZJ one and considering upgrading to that one.

I know the electrical one works, and I have it wired to a switch, and I had to keep that one 24/7 when climbing hills.

jeepme said:

If its cooling while not at speed it usually means a flow problem. Check the lower radiator hose. There should be a spring in the hose to keep it from collapsing. If the spring is not there the hose can callapse and block flow.
I have had the best luck with Robert Shaw thermostats. Did you replace the tranny fluid after it bioled over? if not you definately need to do that.

Click to expand...

The hose I bought didn't have a spring in it, but I just moved the spring from the old one to the new one.

Haven't replaced the fluid in the tranny yet, but planning on doing that in the next few days... (don't really drive much anyways, about twice a week at most.)

HD ZJ fan clutch, NAPA #272310, $44.

ParadiseXJ said:

...and what year is it?

I didn't see a fan clutch in your list of replacements. That'd be my first guess.

Also, put the 195 T-stat back in. It's supposed to be a 195 and changing it to 180 will not limit the high end of the temp. A lower t-stat will just open sooner. Won't help with overheating. Does the radiator leak? Why so many change-outs.

I would tend to doubt the head gasket being the culprit as it would be an issue ALL the time, you'd be pushing coolant, or oil.

Click to expand...

Year: 1994
updated the first post to include I replaced the clutch on it, still thinking about upgrading to the ZJ one though.

First Radiator Leaked
Second Radiator Leaked
Third Radiator Leaked the tranny fluid / radiator fluid together
Fourth Radiator was destroyed in an Accident.

You can put a high-flow waterpump in. Hesco and Flowkooler are two of the more common ones (I have a Flowkooler in mine, seems to help) I also installed a pair of hood vents, helps reduce the underhood temp which helps with overall engine cooling. There are also some coolant additives which can help, I used a red colored one from NAPA years ago, seemed to make a little bit of difference.


On a simpler note, is your radiator cap good? If it's not holding pressure, the coolant will get hotter.

Do you have a transmission cooler?

if your trans is overheating and boiling over, its possible that its putting enough heat into the radiator to make you run warm. Try and put a good transmission cooler in..

I read a few posts about a clogged cat causing overheating

fubar XJ said:

You can put a high-flow waterpump in. Hesco and Flowkooler are two of the more common ones (I have a Flowkooler in mine, seems to help) I also installed a pair of hood vents, helps reduce the underhood temp which helps with overall engine cooling. There are also some coolant additives which can help, I used a red colored one from NAPA years ago, seemed to make a little bit of difference.


On a simpler note, is your radiator cap good? If it's not holding pressure, the coolant will get hotter.

Click to expand...

The waterpump is the one thing I regret, I felt I should have paid for the high-flow one back when i did it, but I didn't.

Radiator cap is good, it's the 15 psi one too, not the 13.

cal said:

Do you have a transmission cooler?

if your trans is overheating and boiling over, its possible that its putting enough heat into the radiator to make you run warm. Try and put a good transmission cooler in..

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I used to, but when I was in the accident in feb, it broke, and I hadn't put a new one in yet... was planning to before summer, but I've had some financial problems... (I haven't been paid since march, but I get paid on Friday they just told me!) Was just going to put in another B&M one like I had before.

ERock62 said:

I read a few posts about a clogged cat causing overheating

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I also questioned this. I don't do emissions testing often (like 3 years ago) as the jeep is registered in a location in cali that doesn't require Smog... Kinda was planning on replacing it when I replaced the rest of the exhaust system.

cal said:

Do you have a transmission cooler?

if your trans is overheating and boiling over, its possible that its putting enough heat into the radiator to make you run warm. Try and put a good transmission cooler in..

Click to expand...

I am with Cal all the way. An over heating transmission could/would cause the engine to over heat.

In one of your posts, you said one of the radiators leaked transmission fluid and water together. Water and coolant mixture could be causing all sorts of problems in the AW4. Try a flush of the AW4 and re-fil it with a good quality fluid. An additional external oil cooler is a must in my mind if you carry heavy loads or assend long steep hills. Is there a way you could verify the tranny temperature when the engine is hot?

You went through plenty of radiators lately. I would look over the entire coolong system again just to be certain that all the pieces are in good condition. And change the thermostat while you are at it.

Tenny said:

The waterpump is the one thing I regret, I felt I should have paid for the high-flow one back when i did it, but I didn't.

Radiator cap is good, it's the 15 psi one too, not the 13.


I used to, but when I was in the accident in feb, it broke, and I hadn't put a new one in yet... was planning to before summer, but I've had some financial problems... (I haven't been paid since march, but I get paid on Friday they just told me!) Was just going to put in another B&M one like I had before.



I also questioned this. I don't do emissions testing often (like 3 years ago) as the jeep is registered in a location in cali that doesn't require Smog... Kinda was planning on replacing it when I replaced the rest of the exhaust system.

Click to expand...

No smog in Cali? I am envious.

Tenny said:

The waterpump is the one thing I regret, I felt I should have paid for the high-flow one back when i did it, but I didn't.

Click to expand...

We use a stock 4.0 water pump with Goatmans stroker when he races. He will run for up to 10 hours at a time, holding over 4,000 RPM's in 2nd gear for loops of up to 50 miles... and it never gets warm.

A hi-flow water pump is the solution to a problem that does not exist, but it can introduce NEW problems.


In theory, you're radiator and your hot sump (the block and head) should hold about equal volume. The thermostat closes, one set of water gets hot, the other set of water gets cooled off. When the engine water gets warm enough, it switches the two volumes of water out and the process continues.

With a hi-flow/hi-pressure water pump, the thermostat often can't close all the way (particularly with Robert Shaw thermostats), and the water doesn't have time to cool off before making it back itno the block, OR, the block won't have time to warm the water up before sending it back to the radiator.. it will run too hot, or too cold.



lets assume that your engine is running correctly, for the moment. The water in the block should be getting hot at a given rate, but the water in the radiator is not cooling at that rate. You have expressed that the fans and radiator are in good upkeep, so we can assume the proper heat is being removed..

but you're still overheating, so too much heat is being added.


Start with the transmission cooler. You know you need it wether or not you have this problem, and there is a fair chance it is a factor if not the exclusive cause to the problem at hand.

Or, ignore me, I'm just a raving lunatic who can't keep his own jeep on the road. (it did however, never overheat).

I also say check the catalytic converter. When mine went bad the first symptom was overheating on the highway. Drove fine around town at speeds under 40 mph but once on the highway the temps starting creeping up. Finally plugged up on the trail and that is when all hell broke loose.

When my trans cooler in the radiator blew it took app. 15 gallons of trans fluid to flush the pink goo out of the tranny. Also not sure if you did, but you will need to flush the entire cooling system in the block. Trans fluid and coolant mixed makes a nasty pink goo that sticks to and can clog everything, and will cause overheating. Took me 4 flushes to get the block flushed completely.

i live in phx so theres not to many other place that are hotter in the summer. i was having probs last summer so i bought a hesco high flow pump way better than the others, mr. gasket t-stat 195* so the water has time to cool in the rad., CSF 3-row rad., new hoses and a good flushing. fixed all my probs even with A/C on 110* plus weather in traffic never over 210*. oh yeah i dont have any hood vents or washers in the to raise the hood.

wow, I am so glad I have a 5 speed (well, I have an AW4 also but not my trail rig)

Well a few updates....

So I put the B&M Transmission cooler in it, and it still over-heated. Not as bad as before but the temps still got up there... (oh and I consider over-heating anywhere around midway between 210 and the red.) But the hill that it did that on, 3 of the 5 vehicles we were with were overheating or very close also.

Still not acceptable. So I put some hood vents in yesterday, and we'll see how it goes this weekend. Hopefully it'll do a bit better, but I have my doubts being that the hood was already spaced up.

Next up is putting in another thermostat (balanced this time) & ZJ fan clutch. After that a new cat ( even if it's not needed, at least it'll run cleaner for the environment... eace: )

jeepme said:

When my trans cooler in the radiator blew it took app. 15 gallons of trans fluid to flush the pink goo out of the tranny. Also not sure if you did, but you will need to flush the entire cooling system in the block. Trans fluid and coolant mixed makes a nasty pink goo that sticks to and can clog everything, and will cause overheating. Took me 4 flushes to get the block flushed completely.

Click to expand...

Yeah I had my friends shop do all that. The Cooling system is nice and clean, as well as the tranny (when I drained it, it was still very bright red, just as clean looking as the stuff I was putting in it... )

Efan on a 2000 doesn't even kick in until 223F. Is your gage even right? Is your radiator boiling over?