Temperature Gauge Spiking
 

My jeep has developed a problem where my temp gauge will read normal (the line above 210 or a little less) and suddenly jump up to 260. This does not happen gradually. I am certain the jeep IS NOT overheating, the gauge is lying to me. I have replaced the temperature sending unit, but the problem still persists. I am not sure where to go from here. Any help would be appreciated. Thanks

The first thing you need to do is verify your temp when it goes up. Use an I.R. temp gun aimed at the t-stat housing. Once you do that then we can go from there. If it isn't reading hot then you may have got a bad sending unit from the parts store or a bad wire or a bad connection?

Year?

Edit: Never mind, I see it under your name.

The temperature jump is a potential symptom of a head issue. What happens is that if you have a leak between your cylinder and the cooling system that opens intermittently, hot exhaust gas will spew into the coolant and boil it, causing your temp to suddenly jump like you're describing.

Or it could be something else. These things are weird.

Are you losing coolant? Has your oil level increased? Are you seeing red mud in your coolant system? If I were you, I'd do the regular tests for coolant in your oil and exhaust gas in your coolant, then go from there.

1998 xj 4.0

Yeah, I saw it after I posted. See my edited post above.

Yep, like Robert said, u need to verify temp. The line above 210 mathematically is 222.5.....which is a little toastier than "normal".

I failed to mention that after a few seconds or sometimes minutes, the gauge will return to normal. I haven't noticed any coolant loss but i cant be positive.

EDIT: more info- the jeep is running completely normal. plenty of power in all situations, just the gauge jumps up. Would a compression test rule out head problems?

Before you worry about anything else you need to verify the temp. You may just have a bad sending unit or bad connections. Without verification you can be going in circles for ever.