Wrench

I have a 99 XJ with 127k when driving it a couple miles it will overheat. You pull over turn it off and turn it back on in less than 2 min the temp. is back to normal. It is getting hot not just a gauge. You may drive 2 miles or 20 no rhyme nor reason. When you turn on the heat it is hot at first then cools off but doesn't overheat because of this. I have searched threads and can't seem to find anyone that has had this problem. Will idle in driveway and never overheat. As of now I have changed
Radiator
Clutch Fan
Thermostat
Water Pump
Hoses
Radiator cap
No water in the oil
No Smoke
Runs great the whole time without missing

Turbo X_J

Thats not really enough information to come to a conclusion. When the problem first occured, what shape was the cooling system in? Meaning was the coolant green or brown, any previous use of stop leak or the like, did the engine over heat, etc.

Wrench

Had it flushed when first bought it and didn't see the coolant, this time it was pale green. No signs of stop leak and yes it did overheat to the first red line but not pegged. It blows the fluid out the overflow tank.

tjwalker

Time for more testing.

Start with a compression test. You may have a blown head gasket. Gotta rule it in or out.

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

Turbo X_J

I would do a compression or even better a cylinder leak down test and see where all that pressure is coming from.

tjwalker

I'm with you Turbo, cylinder leakdown test is definitely more comprehensive, but the compression test may tell the story by itself and is something that every arm chair mechanic can easily do on their own.

Wrench

Alright then compression test will be done tomorrow afternoon and I will report back.