Temp Guage - flucuating?

Thanks for any help in advance.

I've got a 1998 Cherokee sport with the guage package. In the past, the temp guage has always topped out a 210 and has always been steady. once the engine was warmed up. Just recently, I noticed that after warming up, it now sits at about 150. I know the engine is reaching operating temps, and on cold days the heater works just fine. I also noticed that sometimes, when I'm driving down the road or sometimes even sitting at a stop light, the temp guage will slowly move up to 210, then drop to 200, them back to 210, the drop to 150, sporaticly moving up and down. Doesn't seem to be any rhyme or reason to it.

I'm assuming that most likely it's the temp sending unit, so I thought I might replace that. Does anyone have any other ideas, or something else I might consider? I know where the temp sensor is on the 96 and older renix engines, is it in the same place on the newer models?

Any suggestions or help is greatly appreciated.

I replaced my temp gauge because it was not accurate, i would just get a oem mechanical replacement for it at advanced.

Air in the cooling system making steam bubbles, the radiator cap is getting old, or the thermostat is ready to be retired. Your troubleshooting should always review basic maintenance first, then move on to sensor or systems diagnostics. Since you still get a 210 reading, I would guess the gauge and temp sensor are still OK.

mine did that then later it got worse it was jumping around so when i went to replace the sender i noticed that the connector was broke, so i replaced that and it works great now.

It's the sensor. It's only ~$15 at the local parts stores.

I'd try burping the cooling system before moving onto other possibilities. Not saying that is what it is but I always start with the simplest and no-$$ stuff first. Good Luck!

Later models don't generally need burping. I'd make sure coolant level is up, though, because the gauge will drop when it is not immersed. A thermostat problem might make it fluctuate too.

Thanks for the suggestions. Checked the coolant level and it is good. Thinking it might be the temp sensor connection or the sensor itself.

Not sure where it is located, anyone have a picture, or tell me where it is located on the engine.

I know on my old renix it was on the driver's side, towards the front under the intake.

Thanks

The ceramic part on the gauge temp sender at the top rear of the head on the driver's side is known to crack. Happened to mine and a friend's. Creates faulty connection, fluctuating gauge, or just not working at all..or sometimes working fine if it makes a secure connection long enough.

You won't have this extra sensor though if you have a 97+ head.

Well, found the sensor on the termostat housing. Pulled the plug and cleaned the connectors and put it back on. Started up the jeep and ran it for a while and the temp guage went to 210 like it always did before.

Looks like it might have fixed it.

I hope - check it out more tommorrow

thanks for the help