So I have 97 XJ Sport w/ the 4.0 i6. I've been having problems with it overheating since I got it and have been trying to track down and fix the problem ever since, unsuccessfully.
While driving, the temp gauge always shows normal temps and very rarely goes above 210. However, as soon as I park and turn off the engine, after a minute or 2 the coolant begins boiling out of the reservoir. It started as a rare problem and has been happening more frequently, especially after I pull a hill.
Here's what I've done so far:
New Cylinder head (found crack in old one when replacing gasket)
New Valves and seals
New gaskets
New water pump
New T-stat & housing
New clutch fan
New radiator & cap
Multiple system flushes & properly burped
Hoses are good, electric fan works, T-stat seams to be opening properly (hot upper hose, coolant drop at temp)

I'm at a loss now and have done everything I've seen and read about that should fix the problem.
If there's something I'm missing or anyone has any ideas of a peripheral problem that might be causing it I'd appreciate the help. Thanks!!!

 

How good does your electric fan work and does it work ? and what psi rad cap do you have ?

 

To me that sounds like a classic bad radiator cap scenario.
But you say that you replaced it.
So tech asked a good question about what PSI the cap is.
I wonder if it is just defective out of the box.
I say check the cap with a coolant pressure tester.

 

bad rad cap or wrong pressure cap?

 

Thanks for the input guys. In answer to the question, the electric fan is working. I'm not sure what PSI the cap is actually, it came with the new radiator so I never checked it assuming it was the correct one.
I'll pick up a new cap today and let you guys know how that goes.
Thank you!!

 

Okay, so I had a 16 PSI cap, which is the recommended cap from the parts store. I picked up a 13 PSI cap and tried that out, but having the same issue. Everything is fine until I park and shut off the engine, then coolant boils out of the reservoir. I did find a hairline crack in my exhaust manifold, but I haven't read anything yet that makes me think that would be connected to my problem.