I have a 98 XJ with just over 200k on her. Literally the ONLY issue I have ever had with this awesome vehicle is overheating! I replaced the radiator approx 1-1.5 years ago and she instantly ran a little cooler due to that. After a couple months the thermostat locked up and overheated her again. After buying the best thermostat I could possibly find, I've gone a year without having any issues.....UNTIL NOW!

Just a side note, the water pump blew about a month ago, no overheating prior to it though, and I replaced the thermostat again just for good measure when I had that replaced.

Think of the worst possible time for this issue to re-arise....yup you guessed it, I had a potential buyer test driving the thing with me in the passenger seat and she cranked up the heat!! WTF? So my question is what else could possibly be the reason for this 4.0L to be overheating with a very nice radiator, and a brand new water pump+thermostat??

It seems to me like the thermostat is getting stuck shut due to the lack of heat one second and then the blazing hot heat the next (after I punched it to get the darn thing to pop!)

Any input would be greatly appreciated....the guy is supposed to pick it up Saturday!

 

Fan clutch??

 

Thats literally the only other thing that I could think of that would affect it

 

Have you been able to verify that the dummy gauge is giving accurate readings?

 

If the heater is "coming" and "going" your most likely low on coolant and have air in the cooling system. I would check coolant level and look for leaks. Fan coming on? fan clutch?

 

I normally don't post for technical issues but my father in law had this exact same issue. He swapped fan clutches, thermostats, etc.... his had gotten air in the coolant system. He flushed it and refilled it with a tube holding it above to keep air out, heating problems vanished. I could get more details if needed but just trying to share what I knew. Anyways hope it helps!

 

1. What is the coolant temperature on the dash gauge reading? The devil is in the details. Most 4.0 engines run in the 200-210 range. You should verify this with an infrared point and shoot thermometer pointed directly at the thermostat housing to be sure that what you are seeing is accurate.

2. Radiator cap. New? $5.00 part. Get one if you haven't already.

3. If the overheating is only at idle and not when driving, the FAN CLUTCH is the primary suspect.

4. The best thermostat you can get is from your Jeep dealer. OEM MOPAR. 195 degree. Get one. It is the only stat is use and recommend.

 

very true

 

To answer some questions, the fan is coming on and the issue is not at idle, its while I'm driving. Fan clutch ruled out??

Secondly, yes I checked the t-stat housing with a digital laser thermometer and it read 230! The gauge in the dash is dead on the line directly past 210 and I'm pretty sure that it's correct.

As for being low on coolant, I'm not because my overflow reservoir has the normal amount in it and the radiator is topped off. Nobody thinks it could be a sticky POS thermostat?

And lastly, if there is in fact air in the system causing this problem, could anyone give me a detailed description of how to relieve any air that may be plaguing my system??

Thanks again guys! Any and all help is awesome and appreciated!

 

Oh and one more question to answer, there are no leaks within the system.