Stumped...still overheating

Hey guys, after searching through what seems like thousands of posts and trying everything I can...I am still stumped.

Heres what is going on...

1988 XJ, newly replaced 4.0, maybe 12K miles on it at most. AW4 trans...

Never had any overheating problems before....one day it boiled over, and I concluded that the thermostat was sticking closed. Replaced it with a 160 degree stat, at the same time flushed and replaced all the coolant, and burped the system with the nose downhill method.

Went for a whole summer with very little problems, maybe getting to 200-210 at the most while wheelin at slow speeds.

Well, Trans started to get hot, so I installed a aftermarket cooler. Temperatures underhood rose, as expected, so I installed a 10 inch auxillary cooling fan, helped maintain the temp at about 200 on highway and 215 while wheelin.

While making a trash run one day, the jeeps temp rose incredibly quick, I switched on the aux fan, no help...steam began blowing out from under the hood, as the coolant boiled over out of the "turtle" as some would call it.

Temp gauge was in the red when I was finally able to get off the highway.

Sat for 45 minutes while the truck cooled....topped the water off in the reservoir, drove back to the house, had to stop 2 more times as she boiled over before I actually made it home.

All hoses had pressure on them, belt tension is good, water pump is good... pulled it out this afternoon just to be sure.

Heater core has been bypassed, no cracks in the reservoir, replaced t-stat with a factory 195...burped it every time that I have replaced coolant/water.

Tried everything that I could think of, but cannot get it to stop overheating. Its a closed loop system, but it just consists of reservoir engine block/head and radiator...no heater. No AC either, took all that out.

The only conclusion that came to mind from reading the posts is the radiator...So, took it to a local radiator shop, the tested it, said it had good flow and held pressure....doesnt mean its good right?

I am stumped...this is my daily driver, but here lately its just sitting..with a puddle of coolant under her.

After the last overheating excapade, it started sputtering real bad at idle, and blowing a hell of a lot of white smoke....

Dear god not the head gasket...

Dont even want to fool with that unless I know what might have gotten me here in the first place....

Any help would be most appreciated.

white smoke out the tailpipe certainly sounds headgasketish. Have you checked the oil for coolant?
Pull the spark plugs. If one is a whoe lot cleaner than the other then that's an indicator of coolant in that cylinder.
Be a good idea to do a compression check.

Since you have checked most other things that would contribute to that quick of an overheat, I have to also say it sounds too much like blown head gasket as well.

A pressure test should reveal more results, or get the chemical test done to see if exhaust gas is present in your coolant.

As far as knowing what got you to this point in the first place? Well, those earlier overheats probably warped the head slightly, and over time, the gasket just gave way.

Okie dokie....well will do a compression test this afternoon, what should I expect from a pressure test? What pressure range would be right? Any tips for replacing the head gasket?

Just because a rad has good flow does not mean it's still a good rad. The copper fins tend to rot or go bad, old rad guy around here showed me a trick using my thumb nail, gently run your thumbnail backwards over the fins, enough to deflect them a bit not bend them over, if they stay bent then the fins are rotten and act more as an insulator then a heat transfer.
As for the turtle, they do go bad and once they warp from overheating I think they are pretty well finished...

Moore4X4 said:

Okie dokie....well will do a compression test this afternoon, what should I expect from a pressure test? What pressure range would be right? Any tips for replacing the head gasket?

Click to expand...

Pressure testing is done by pumping the system up to 15 psi and watching the pressure gauge for leakdown.

cylinder psi should be between 120 and 140, cylinders should be relatively close to eachother.
Taking the head off shouldn' be that difficult, just a PITA, you'll have to take off the manifolds, or get a few friends to help you pull the head with them on. I've not taken mine off, but I have a spare head here, and it weighs a ton!

Stumbling, white smoke, temp guage quickly flying into the red and boiling over...

Yeah, sounds like a head gasket, cracked head, or cracked block to me.

Grrrr. Well, found a wrecked 93 2wd with a fresh 4.0 (8,351 miles on the new motor when it was wrecked) and good trans for 400.00.

Maybe I will buy it and swap the bastard out.

Are the oil pans different? IE 2wd vs 4wd pans?

Hell anyone wanna buy it the way she sits?

Thanks for the help BTW...