Erratic Temp Gauge on 98 XJ

[Lost_Wrench]

Yesterday on my way home from a trip to Utah my temp gauge randomly started reading about 140 for running temp. Once in awhile it will spike up to 210 for a minute or two and then drop back to 140 or so. It is a 195 degree t-stat. After it has been reading 140 for awhile I turn the heater on and it is definitely not very warm which makes me think it's a malfunctioning t-stat. Once I see it spike up to 210 I turn the heater on and it is warm. Gotta be the t-stat right? I purchased a new 195 t-stat but haven't installed it yet.

 

[Unclewolverine]

It's low on coolant.

 

[Tim_MN]

I almost never recommend installing random parts with no diagnostics, but thermostats are cheap, easy to install, and the symptoms are what one might expect for a failed thermostat. When my 00 had those symptoms, the thermostat had broken apart.

 

[Wayne Sihler]

On my 98 its usually the connection on the sensor is corroded. un-plug>plug back up good to go.

 

[SleeperXJ]

Had this same thing happen today on my 99 XJ. Plenty of coolant so I tried disconnecting the sensor at the tstat housing and re-mating, that seemed to fix the low reading.

 

[Lost_Wrench]

So I topped with coolant but it was only a tad bit low. I unplugged the coolant temp sensor and inspected, no corrosion. I was about to replace the thermostat but now everything seems fine. Air bubble? I'm keeping the thermostat/gasket and tools to change it out with me in the Jeep for awhile just to be safe.

Thanks for the responses.

 

[Tim_MN]

Wire plug corrosion does happen.

The Cherokee open cooling system is self bleeding, after a few start/run/stop cycles of driving any air bubbles are purged.