UPDATE:
Got some more work done on it this weekend. The combustion leak test appeared to be negative, although I wasn't able to get the motor fully heated before the radiator started boiling all of the coolant out. Tried it again AFTER it boiled all the coolant out and still appeared to be negative. So I swapped the damn water pump, no improvement. The old WP looked fine. Burped, vacuum bled, and opened the thermostat bleeder valve repeatedly, still no better. Don't see how it could be the radiator since it holds pressure and vacuum well, has excellent flow rate when flushing, and looks clean enough to drink out of (I'm about to drink the orange Kool-Aid dealing with this nightmare!!! )

I guess I am going to try swapping the Autozone thermostat with a MOPAR unit. Maybe also see if I can get a more definitive combustion leak test without boiling over. Otherwise I am at my wits end here and about to take it to a Jeep shop to see if they can help figure it out.

I do have an exhaust leak and have recently read about bizarre situations where this can cause overheating. Is anyone familiar with this?

 

you should be doing that combustion test via the reservoir, not the radiator.

 

Resharp001,

Got it. I thought that may be better since it would allow me to get the motor heated up, but the kit specified with the radiator cap off oddly. I also wasn't sure if that would just be fresh air in the reservoir since it's exposed to the atmosphere from the overflow tube. I'll try another combustion leak test from the reservoir and swapping the thermostat to MOPAR here in the next day or so.

 

Do you check or change the radiator cap??

 

Yep, already swapped it.

 

Combustion leak test was negative again. Pulled air through the reservoir while I had a friend hold his foot on the throttle to get the motor overheated after driving home. Pulled about 50 bulbs of air through the test tube. See pics below. Guess we'll see if the Mopar thermostat does the trick.

 

UPDATE: Swapped the AutoZone thermostat with a MOPAR unit. The one from AutoZone was pretty clearly inferior, didn't even look quite the same. At first (like you described) it would still overheat, but this has gotten progressively better over a few bleed cycles. It is mostly fixed but still does overheat a bit more than before when climbing hills on the highway.

Any other ideas? At least it is drive-able now!! Thanks for the help/input from all of you!

 

Can't recall, but do you have anything blocking the radiator? winch? aftermarket grill? bumper? etc. My first thought now, if you have the system burped correctly and the thermostat is opening all the way, is that it's an airflow issue. Even those cool little grill inserts will make a huge difference on the highway. Remember that these jeeps are designed to run at a higher temperature already, so anything added to the front will reduce its ability to do so drastically. Larger tires, lower gears will add to the struggle as well.

 

I do have one of the mesh grill inserts (but it has fairly good airflow) and a winch/bumper but they never seemed to cause trouble before. Maybe I'll experiment with pulling the grille and seeing what happens. Thanks again!