'92 Cherokee the Jeep will run a little over 210 and then if you hold the gas down at about 1500 rpms it will drop down to 180 "ish".

Thermostat sticking OR water
pump?

Thermostat opens then dumps cold water into block from radiator. Temperature will drop. The faster you pump the cold coolant from the radiator the faster the temperature drops. Then thermostat will close and the process will repeat.

Forgot to mention my engine runs around 220. When thermostat opens it drops below 200. It depends on the thermostat you're running. I always go with original equipment. I do believe the original equipment thermostat for the 4.0 opens at 210. Could be wrong.

Yes, I understand that. Its a 195* tstat which means it should open at 195. I know the factory gauges aren't 100% accurate but this isn't normal for this jeeps temp gauge to read that high, its apparent when it opens because it immediately drops down. When holding 1500 rpms the water pump spins faster and pushes more water. I think the tstat is sticking closed and when enough water is pushed it opens?

Does it do this all the time or just on initial start up? If it does this on initial start up it is "normal" (especially with aftermarket stats). If it is doing this all the time you may have a sticky thermostat, worn water pump impeller (the impeller is metal and corrodes over time, so blades may be missing even if the bearing is still good and it isn't making any noise), or a worn fan clutch (slipping and not moving enough air at lower rpm). If this is the case and you don't know when they were last done it wouldn't hurt to replace all three.


You are correct on the OE temp for the thermostat, it is 195 degrees, though it is relatively common for stats (especially after market ones) to overshoot slightly (especially on initial warm up) and open at around 205 to 210 (part of this is due to location, the sender for the gauge is on the back of the head, the thermostat is in the output housing so there is a slight variance in temp between the two locations).

Wonder what's making coolant temp go to 210 this time of year? Almost sounds like a air flow problem thru the rad when the motor is at idle. How old is the fan clutch? Is the fan shroud intact/in place? If u r running a 195 stat, something is wacked if temp drops to 180.

Temp probably drops back to 195* ish. Why shouldn't it run around 210? That's operating a temperature which is where its designed to run and everything is designed to function best?

Yeah I'm going with this guy. On cold mornings the first time my thermostat opens it drops down into the 170s.

Replace both water pump and the thermostat, flush the block and rad at the same time Can't spend too much money on XJ cooling!

However...

djb383's right. Does this happen at highway speeds or just when sitting still? If this problem doesn't occur when driving a fan clutch is likely.

It happens when driving or sitting still. The radiator is new and the block was flushed when I put the new radiator in. I'm going to try a tstat tomorrow.

Salad. Where did you get that quote from? Easy Riders? Fear and Loathing In Las Vegas? Swear I heard that somewhere before. Don't mean to hijack your thread.

Yes our dear buddy Hunter S Thompson

Love that Man's work. Goes good with an XJ Forum.

I can see temp dropping back to 195ish (not 180ish as stated in OP) if a 195 stat in installed. What/where does it say the XJ is designed to run at and function best at 210?

I interpreted the OP as the vehicle being stopped/idling and temp would reach 210........then increasing rpms from idle to 1500 would bring coolant temp down to 180. Reaching 210 then dropping to 180 just doesn't sound right in cool/cold ambient temps using a 195 stat. If the fan clutch is in functioning properly and the fan shroud is intact/in place, coolant temp reaching 210 (actual) doesn't sound right in cool/cold ambient temps. Likewise, dropping to 180 using 195 stat doesn't sound right in cool/cold ambient temps. The stat open/close temp can easily be tested/visually inspected in a pan of water on top of the stove using a cooking thermometer. Be sure to test a new stat before installing.