I'm a bit worried about my xj. I was driving in stop and go traffic today with my ac running witch I do often without a problem. The engine runs at about 220. Well today it was doing the same then suddenly shot up to 250 and the check gauges light came on. I turned the ac off and cranked the heat. It suddenly dropped to 220 once again. This happened about 2 years ago so I did a coolant flush and a new thermostat. What could be causing this? Electric fan is working and coolant is full. Any help would be great I don't want to kill my engine

 

was just covered.....https://www.cherokeeforum.com/f2/ins...erheat-140598/

 

Thanks man ill try replacing the temp sensor. Autozone sensor good or should I go to jeep for this? I ask because I know the autozone oil pressure sensor sucks.

 

Don't get any sensor from Autozone. I've had bad luck with their oil pressure sending unit, throttle position sensor and coolant temperature sensor. And then I finally learned my lesson.

How quickly did it shoot up to 250? If it was within 1 second, I'd say to replace the sensor at the rear driver side of the head. If it was somewhat gradual, I would say that you may need to do some maintenance.

When was the last time any other cooling system maintenance was done? Radiator, water pump, mechanical fan clutch...

 

Mike make sure you have 12.5 quarts* of 50/50 coolant.

 

It was very sudden. Within a second or 2. Rediator was flushed as well as the block and heater core last year. Never touched the water pump at all or the machanical fan clutch. So the sensor u say is located at the back of the head? What is the one on the thermostat housing for?

 

"The computer will bump the gauge way up and light the check gauges light when it reaches a certain threshold. This makes sense to me as the gauge creeps up under load until it gets to a needles width over the 220 line and then bang."

"Yours is buffered by the PCM and once it crosses a certain threshold the needle is driven far right and the light comes on.
You are probably not really operating at 260 deg, Chrysler did this so the "average" driver could easily see which gauge reading was out of bounds. "

Basically once the gauge reaches 221* it will spike to get your attention. try testing with temp gun to see for sure.