temperature fluctuation?

so the second to last thong to do to get the heep ready for the summer is my temperature fluctuation deal i have going on. i have a 97 cherokee, 4.0l, aw4, np231. whats happening is, when im driving up longer hills, my temp gauge goes up to 210 and stays there. when im cruising at normal driving speeds, the temp gauge reads the mark before 210. and when im going down hills or am off the gas, it drops down to two marks above 100* what ever that measures out to be. what do y'all think

Have you done any cooling system work on it lately? Thermostat been changed lately? If not, do so. I like the Stant Superstat as well as stats purchased directly from Jeep. 195 degree only.

If the temperature drop on the gauge is almost instantaneous, the problem may not be a real temp. fluctuation, rather an electrical problem.

I use an infrared point and shoot thermometer pointed directly at the thermostat housing to verify coolant temp. Raytek MT6, $50, best money I've spent for analyzing cooling system problems.

If it were mine, after verifying/replacing thermostat, I would remove the connector from the coolant temp sensor located on the thermostat housing, clean it thoroughly and reconnect with a dab of dielectric grease.

Normal operating temperature 205~210, climbing a hill should raise it.

I would not expect to see a substantial drop coasting or going down hill. You "temperature gauge sending unit" is actually the CTS, coolant temperature sensor. It feeds data to the PCM and the PCM feeds the temperature gauge.

I would replace the thermostat, Stant SuperStat Premium 195 degree, and see what that gets you. The Stant SuperStat has built in provisions to level-out temperature swings.

Of course a good inspection of the rest of the system is never a bad idea.

Gradient wise, 1st mark is 100F, 2nd mark is 137F, 3rd mark is 174F, 4th or mid-mark 210F, 5th mark is 227F, 6th mark is 244F and 7th or last mark is 260F. Gauge in the middle or slightly lower sounds normal for the factory gauge.

thanks. the only things i have done to the cooling system lately was last summer. i replaced the radiator because it blew up and i put a 180 t-stat in because i was having cooling issues last summer and i didnt know much at all about things so thats what someone told me to do. and all the information i posted was based on on-road driving. i have not bee wheeling yet this year so i dont know how the temperatures will change once it warms up.

rcliftedXJ said:

thanks. the only things i have done to the cooling system lately was last summer. i replaced the radiator because it blew up and i put a 180 t-stat in because i was having cooling issues last summer and i didnt know much at all about things so thats what someone told me to do. and all the information i posted was based on on-road driving. i have not bee wheeling yet this year so i dont know how the temperatures will change once it warms up.

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Yeah, common error is trying to fix a cooling issue with a lower thermostat, all that does is delay the overheating. Lots of threads on here on cooling system maintenance/upgrades.

Good luck.