When I drive my car for over a half hour, and start doing some serious city stop and go driving, my car runs hot, but not to the point where the temp gauge will reflect it. The reason I know it is a problem is if I stop the engine, then try to restart it. It cranks but doesn't start, and I get an error message on dash saying something like it's in some engine disabled mode. After waiting about a half hour, it cools down to the point where it'll start back up.

Thermostat, Water pump, thermostat housing, AND THE ENGINE were replaced almost two years ago. This problem started after that work was done. I've had hoses changed as they've ruptured since the engine replacement, probably from the high heat.

The system has been pressure tested, it's good. Mechanic claims the radiator is working fine.

I've had it at an independent Jag mechanic for about two weeks and he said something on the phone the other day about some water/coolant tubes between the heads but I didn't understand him.

Does anybody have any clues as to what it might be?

 

Step 1: Read the OBDII fault codes. Post them here for advice.

 

Fuel Pump return valve gone bad. That's my guess. I, and many others have gone through it.
Does it start quickly after sitting? or when the engine is cold? Try running you car as you usually would. Shut it off. Immediately try starting it. It should start right up. Then drive it again. shut it down for a few minutes and try to start it. If it won't start,you've found your problem.

 

The fuel pump return valve issue only applies to the 4.2 liter (2003 and later US, 2002 and later UK) vehicles.

 

Sorry XK, I missed the year of his car. As usual, you are correct.