Areyna23

99 XJ sport 4.0 4x4
I notice my temp gauge in the cluster board started fluctuating a few days ago. The jeep wasnt overheating, just the gauge going crazy. I replaced the coolant temp sensor and connector, serpentine belt, idler pulley, water pump, water pump pulley, and thermostat. It is still doing the same thing. The temp gauge is still fluctuating and the serpemfine belt is now squealing, especially when i turn on the A/C. How do i knw how tight to put the serpentine belt, anx what can be causing that temp gauge to go up and down.

jordan96xj

A squeaky belt after a belt change is pretty common. Especially when AC comes on and puts more load on the belt, and then even more so if the air has a lot of moisture in it. It probably is not related to your temp gauge bouncing around. Having a belt tension gauge is handy for the XJ because when done by "feel" we usually don't get it tight enough. But if you go overboard and really tighten it down, you can do damage to the pulleys/bearings as well.

For the temp gauge problem I think you should get a cheap OBD2 scanner so that you can see if the computer itself is logging strange data values for the coolant temperature. This would cause your computer to command the temp gauge to do strange things. If the computer values are normal, then I would begin suspecting general electrical problems, or a failing gauge.