xj Temp gauge behaving erratically - JeepForum.com
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post #1 of 4 Old 07-28-2020, 02:22 PM Thread Starter
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Location: Tucson
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Xj xj Temp gauge behaving erratically

The temperature gauge of my 98 xj has been dropping suddenly all the way to the first line after reaching 195 - 210 degrees, sometimes it stays on the first line for the rest of the day or goes up just a bit above the first line and sometimes goes back up all the way to 195 - 210 just as suddenly. Some days it does it some other days it does not.

It all started after I took the car to my usual mechanic to check the cooling system as the jeep usually overheats during summer season ever since I bought it; the guys at the shop told me that the fan clutch, the electric fan, and the radiator cap were bad. They replaced the fan clutch and the radiator cap the same day but not the electric fan. After a couple of days I noticed that the fan clutch was locked-in all the time and that's when the problem with the temp gauge started. I took it back to the shop and they told me that the erratic reading of the temp gauge could be due to the fan running at full speed all the time thus keeping the engine cool. They replaced the defective fan clutch and also installed a new electric fan, and during the next couple of days the problem seemed to have been fixed. All of this happened when I was about to move to another city, and so on the last day of my road trip the problem came back and the temperature gauge is erratic again, dropping suddenly and going back up suddenly, or just staying at or below the first line.

As I mentioned before, I never had this problem until the fan clutch and the radiator cap were replaced. Unfortunately, I cannot take it back to the shop as I am now 2000 miles away. Does anyone have had this problem before? Do you have any ideas on what could be causing the erratic temperature readings?

Last edited by IsmaSanz; 07-29-2020 at 01:17 PM.
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post #2 of 4 Old 07-28-2020, 04:42 PM
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2000 XJ Cherokee 
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Location: out in the garage - Minneapolis
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I would suspect either the thermostat, the radiator cap, or the Coolant Temperature Sensor (CTS) on the thermostat housing.

Make sure the CTS wire plug is tight, and that there are no issues with the wire insulation that allows bare wires and that there is no corrosion in the CTS wire plug.

I would replace:
The thermostat with a genuine Jeep or a STANT 195* thermostat.
The radiator cap ( should be 16 lbs rated).
The Coolant Temperature Sensor.

“When the people find that they can vote themselves money, that will herald the end of the Republic.”

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post #3 of 4 Old 07-29-2020, 01:15 PM Thread Starter
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Thanks a lot for the advice CJT-Tim. I got the new thermostat and sensor and will be installing them this week. I will post an update afterwards.
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post #4 of 4 Old 08-03-2020, 10:31 PM
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That mechanic took you for a ride if he told you that. Coolant temp sensor in the thermostat housing. I have had a few act up like this and I usually got away with wiggling the wires back down real good.
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