Hey everyone, I'm working on my girlfriend's jeep. It is a 94, 4.0, 4x4, 5speed. To start off, I know a good bit about auto mechanics in general. I was a tech for a while but I mostly worked with newer imports. Computers did the diagnosing for me. lol Anyway,

All was well with the car until one morning we started the car and it was burning coolant. A consistent white smoke from the exhaust that increased with revs. Smelled like coolant and there was a lot of pressure in the radiator. Oil was very clean with no signs of coolant. The coolant however was brown and had chunks of a gritty substance. My guess was it was some sort of STOPleak additive. The car, even at this point, was running perfectly fine. Smooth revs, no miss-fires, etc. But it wouldn't stop burning coolant or creating a ton of pressure in the radiator. It is possible the car overheated at some point due to the fact that it is a base model with no "real" temp gauge. Just the red "oh ****" light. But for the record, that never came on. It may have never even worked.

I immediately thought, the head gasket is done or the head has a very small crack.
We left the car and continued the day in my car. The next day I started up the car and there was no sign of burning coolant, no pressure in the radiator, no issues at all. I drove it for awhile, let it idle for awhile, and still nothing happened. I ran a leak down test and it showed no exhaust gasses in the liquid.

I flushed the radiator to see if I could get whatever gunk was in there out of it. I pulled the thermostat housing and found that gunk EVERYWHERE inside of it, the thermostat gasket was falling apart and bits and pieces were loose inside the housing.

For peace of mind I decided to pull the head. I had it checked by a machine shop and they said it was crack free and everything was in pretty good shape. Only issue he saw was that the surface of the head was some-what far off in the center. He thinks its possible that the head may have lifted and cause the gasket to let go.

The gasket was a metal gasket and seemed to be intact, it was definitely old, but I don't know if it was bad enough to let coolant through. All of the head bolts were tight and required the same amount of effort to get off. The coolant jackets were all dirty with, again, that STOPleak gunk.

Also, to note, when I pulled the head off, I did see a good bit of coolant on 2 cylinders. But, that could have just been left over coolant in the water jackets that drained out when I lifted the head off, however, the others were all completely dry.


At this point, I am not sure what to think. I plan on replacing all necessary gaskets and hoping it all goes well. But I don't want to feel like I wasted time and money if this happens again.

Can any of you far more jeep-savvy people shed some light on this? I've done a good bit of searching and haven't had any luck. So now I am here.


I apologize in advance if this is the wrong forum to be posting in.

Thank you!

 

still scratching my head on this one!

 

You did have the head resurfaced at the very least didn't you if it wasn't true?

 

of course, the heads being completely re-done. valve job, shot-peen, the works.

 

Can't help with your problem, but FYI:

Good guess, but probably wrong. That brown crap is what is left behind when the water boils out of your coolant. That doesn't necessarily mean that you overheated the entire motor, only that the water reached boiling temperature somewhere in the system. If the system is not properly pressurized (which it's not if you have a leak somewhere), the water will boil at 212°, while it would boil at a much higher temp if the system is properly sealed up.

 

Interesting, thank you for the information.

So clearly, the engine has overheated at some point. So I guess its good I pulled the head and assumed a head gasket. Hopefully this fixes the issue. I'll be upgrading the cooling system while everything is apart and getting a decent digital temp gauge to properly monitor temps..

Thanks again for the help.

 

Did you perform a compression test, if so what were the results?