austinjoe13

So I've noticed a LOT of overheating threads in the past month and have learned a bit about what causes them. I thought it would be nice to have A thread dedicated to overheating issues.

Before I start listing causes, if you're new to jeeps or cars in general, don't slack on maintenance. Trust me, it cost me a jeep. Before you have overheating issues, have your system flushed every 36k miles or three years, whichever is sooner. If it's a renix XJ (87-90 4.0L models) you call a DD then maintenance should be done religiously. 50/50 mixtures are very common, but if you live somewhere that sees temperatures below -25F it will freeze, so you lucky guys and girls get to run 70/30 . If you're a DIYer use pure distilled water as minerals from well water like to deposit in things like the radiator, heater core, everywhere. Running pure water in the system is fine in a pinch, but drain some out and refill it with coolant later. Water just doesn't transfer heat like antifreeze does.

Always check your coolant level and condition before throwing money at your vehicle. Never open a system that is under pressure.

Alright, now we're onto the good stuff. Situation One: your jeep runs hot or cold all the time regardless of ambient temperature. This is a telltale sign of a bad thermostat. People will fight to the death over what temp stat to use, but the 4.0 came with a 195F from the factory. Thermostats can be faulty right out of the box so maybe buy two or three and boil them in water to see which ones work and which don't.

Situation Two: it's always warm or hot. This can be a little trickier as leaks in the system will cause a rise in temperature. For every psi of pressure applied to water the boiling point is raised 4F. The first thing you want to do is remove the serpentine belt and check for play in the water pump pulley. If there is slop, replace it. If not, start looking and listening for leaks. When you get done driving it pop the hood and listen hard for hissing. Both my renixes have hissed at the pressure bottle overflow hose. In my experience this doesn't affect it much but tighten the hose clamp anyways. You might as well tighten everything while you're in there, it'll take all of five minutes. Another cause for always running hot is a bad radiator cap; it could be stuck open or the spring is weak. Most caps are 16psi (16psi x 4F/psi = and extra 64F of boiling temperature). They're cheap and easy to replace. But don't be that guy who opens it right after shutting down, you will be severely burned.

Situation Three: overheats in traffic but is fine on the highway: most likely the mechanical fan clutch. Lots of guys upgrade it with a ZJ clutch. The weight of that fan spinning saps power, so some guys opt for an electric fan instead. Many write ups can be found on that subject. Another thing to check out is the electric fan. It turns on at 220F I believe via sensor and relay, both of which can go bad. A good test for that system is to turn the AC on and listen for the e-fan. Replace the relay if nothing happens. If it passes that test, but still doesn't turn on periodically without AC try a new switch, located in the radiator on the driver's side.

It's 2:10am right now, I'll be back later to add and edit.

Finally, the best way to solve a problem is to find others with the same problem and learn how they fixed it. Share some stories and pass some knowledge.

DISCLAIMER: I only know what I have read often. I am no cooling system guru.

To save a little money, buy straight coolant. $12 for a gallon vs $8 for half water and half coolant.

Bob98Classic

Good write up. I read that 50/50 premix manufactures do not use
or recommend distilled water, but use filtered tap water.
I use filtered rain water myself. Tap water here is very bad.
I have been flushing my cooling system out often this summer, and
will add 50/50 soon before winter.
There is one coolant manufacture that has a no water coolant, "Evans".
Expensive, but states no corrosion. I guess this could be true, since
no water is used.

nitroxsteve

I would like to see that recommendation, because all engine manufacturers I work with recommended distilled water never tap or hard water.

DougyFresh

what about this situation...

Stays under 190 idleing. It can sit and idle all day perfectly fine.

Get out on the road and it overheats. Doesn't do it all the time, maybe one out of every 15 20+ mile drives

austinjoe13

Do you have the heat or AC on when this happens?

Cjjcalhoun

I am a proud first Cherokee owner. I purchased my cherokee from a friend for $400. It was overheating and she couldn't drive it. Her mechanic said it had a blown head gasket and she couldn't afford the work. I like to tinker with things so I took it on.

I started by removing the head. Didnt check a thing, just jumped right in. To my surprise I found nothing wrong with the gasket. There was no thermostat installed in the head, but that was all I could find wrong with it. I figured the overheating problem she described was caused by something else. I cleaned the head and replaced the valve seals (included in the kit) and reinstalled with a new thermostat and gasket.

When my first repair was complete I looked for other problems that could cause the overheating condition. As soon as I cranked the engine I saw coolant flowing from under the cap (on the overflow tank, sealed system). I bought a new one, installed, cranked the car, and the new cap blew off. I figured this must be the cause of the over heating. I ordered a new overflow tank and cap. When that was installed I took the jeep for a test drive, very confident that I had repaired the problem. I was mistaken. I got about a mile.

At this time I start scratching my head, so I came to the forums. I read about jacking up the back of the jeep to make sure the coolant system is full. I did that with the same results. I read about the clutch fan, so I checked mine and it seemed ok. It didn't have an exorbitant amount of tension but it isn't a bran new jeep either. I also read about having a water pump that turned the wrong way. I removed mine to only be disappointed yet again. Since I had the pump off I bought a new one and put it on because it was only about $30. This time I ran my jeep at my house, at idol, for 30 minutes with no problems. I got excited about my dumb luck and took it out for a test ride. I made it about three miles before it overheated.

Still scratching my head I decided to go ahead and change the radiator. My fan shroud was in bad shape as well so I changed it too. Took it for a test drive... 3 miles later it was overheating again.

So today I used my last glimmer of hope. I too out my freeze plugs, just hoping to find something to explain this problem. I found nothing. Then I thought "you idiot- it's got to be the thermostat" so I took it out and boiled it. It worked great.

At this point, I figured I had covered every possibility, so I started over. I took my spark plugs out, tested my compression, and this is what it got: #1 170 , #2 145, #3 160, #4 165, #5 140, #6 135. #6 is the only one out of specs so I added a little oil to it and it was good which means it has bad rings. And for this thing to be running hot that quickly I am sure that I would be looking for a huge difference.

Couple of things I do need to add in, every time I would overheat I would loose water through the cap but wouldn't loose any until it was overheating. I have no white smoke coming out of the tailpipe either. My electric fan is operated by a toggle switch under my steering wheel and I kept it on through all of these tests.

Any ideas?

Bob98Classic

Prestone, John Deere, Delo-Extended use "demineralized" water.

GM Dex-cool, Castrol, Polaris, use "de-ionized" water.

I am sure none of the above companies would want to use the water

from the river near me for their water supply. Cow country here.

I do not recall where I read about the distilled water....

nitroxsteve

I have gone to school for JD and Cummins engines and distilled is all we were ever told to use I guess if your filter gets all the minerals out that would work too. Just never thought a filter was good for this. Hard water causes cavitation.