My temp gauge is acting wierd. When I an setting at an idel the temp gauge shows about 190ish (normal). But when I start going down the highway the temp gauge drops to about 115ish and stays there at highway speed. Anyone have an idea or can help with this issue so it don't cause other issues?

 

sounds like your thermostat is stuck open - you need a new one

 

X2

 

Seems like actual coolant temp would be more than 115ish even without a t-stat. Could be gauge/sending unit/electrical problems as well.

 

In the winter in who knows where since it's not in his sig or avatar? Could be that low depending on where he is.

 

.......could be, but doubtful, it's an XJ.

 

Maybe it's a bit of both. OP, how well does your heater work?

 

Heat seems to work well. Have plunty of coolant.

 

Then it's not actually running 115*.

 

so is there a sensor that need to be changed out ?

 

I believe on '96 down the temp gauge/light sending unit is in the back drivers side of the cyl head and the coolant temp sensor for the ECU is in the t-stat cover. '97 up only have a coolant temp sensor in the t-stat cover.

A infrared point-n-shoot temp gun ($25-$30) is an extremely valuable tool to diagnose coolant temp issues from a stuck t-stat, plugged rad/heater core to electrical/gauge issues and just about anything in between. Handy as a pocket on a shirt.

 

^^ X2

 

So what am I looking for with this tool? I understand how it works but how do I know whether something is bad or good when I'm pointing it at an area?

 

The gauge hasn't acted up for a day or two now so Idk what is up to. Just waiting for it to do it again I guess. And if it is only doing it when I'm at highway speeds how do I find it when its at an idel if it work correctly at idel?

 

You are looking to see if the gauge is telling the truth.