Ye Ol' Cherokee

98 4.0 xj

I posted earlier, but with no hits, posting a short version, so maybe I can get some help.

My temp sensor croaked while on the highway, so my engine overheated and I didn't know it. I got home, it spewed coolant. It overheated anywhere from 1 - 30 min.

Now a few days later, it has intermittent rough running. Sometimes I'll start it and the rpms will drop then jump, etc, while the engine is bucking and puttering. I have no codes. It will occasionally do this while driving. Most of the time though, it runs like a champ still. Replaced oil and trans fluid, no sign of coolant in oil

please help! Headgasket? Head? Or something less serious like a melted sensor or baked spark plug ?

Donovan Claiborne

Same issue but have not fixed it yet. Once I figure it out I'll update

tjwalker

Start with a simple compression check. If it's a headgasket, a compression test can often snake it out.

The compression spec. for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.

What did you find as the "root cause" of the overheat?

Donovan Claiborne

Got it from my dad because they quit driving it. It did not make it home 2 miles up the street without running really hot. I'm not sure how many times people ran it hot before I got it which is bad... It is on its 3rd motor by the time I got the Jeep. I have been trying to get it for years and finally got it.

Overheating was caused by trash in the overflow. It was allowing coolant to enter but the trash would stop up the hose and stop coolant from coming back into the radiator.

Using a waterhose with a few attachments cleaned the overflow tank, back flushed the cooling system, and was shocked at all the rusty trash that came out. Back flushing the heater core actually made the heat work again. There was so much trash inside the heat barely blew luke warm air!

Compression check is a genius idea I will have to check that.
I didn't think to do that yet I appreciate the reminder!
Its rare but does seem to happen on low RPMs which would line up with compression issue. I do not think its ever missed under heavier accel.