Well I had an interesting ride today. Looked down and temperature was pinned at top of hot on the guage after a short errand.

A quick check just confused things. RealGuage alarm silent. Air-conditioning working (it auto shuts off if overheating). Fans weren't even on (by then I had heater on no a/c).

A short ride dropped temp indicator just below red zone. Engine running fine. I shut it off - temp guage was stuck(?) Just below 3 o'clock position.

By then I was convinced of faulty reading. Drove home. No issues. It was like the needle worked normally (i saw it move 5 degrees as thermostat opened closed).

When home immediately grabbed IR temp gun. Nothing was above 208 degrees, hose temperatures showed coolant was circulating.

Turned air conditioning on, yes fans work.

So, letting it get back to room temperature. Figured I'd launch this in case anyone recognized it.

After 30 minutes I looked again. Guage still sticking a few hash marks above cold with key off. Cycling key OFF on off, I could see the indicator stumble as it tried to get to zero when ignition off.

Thinking out loud, if Guage goes to zero with key out, I'm not sure how anything that feeds the guage can be at fault. I mean even if temp sensor is faulty, guage should need power to read anything. It is a switched circuit right?

Any thoughts?

John

 

Disconnect the battery for 30 seconds and reconnect it (don't forget to reset the windows). Then see if it is back to normal.

The gauge controller chips (both in the Jaguar cluster and Realgauge) have been know to (very rarely) get their memory corrupted and the battery disconnect will restore it.

 

Great idea!!! I'll let everyone know how it goes.

Thanks, John

 

Does that explain why for no reason my temp gauge will hit the red and the car will say it's overheating when it ciertianly isn't. Only seems to happen on really long road trips. 1000 miles plus? If I turn the engine off and back on again it clears every time.

 

You should check the temperature being reported over OBD to see if it's the sender or the gauge, using the Torque app and dongle or one of these cheap plug n play displays:-

 

I'm told that guage is not a real fluid gague but only a multi position idiot light for what thsts worth.

 

Could it be the coolant temperature sensor? My temperature gauge did all kinds of weird stuff before I replaced it.

 

I replaced that last year because of the same thing. Do you think it could fail again so soon? Only seems to show up on really long trips though, it's not done it since trying to and from work.

 

Mine would only give me false readings on long drives as well but mine would mostly go the other way, to the bottom of the cold side of the gauge. It would be fine until I drove about 60 - 70 km and then the gauge would start to drop. I replaced the cross over pipe with the sensor installed and it solved the problem.

 

I might have to get another sensor then at some point. I'm not going to chase all the problems around though, you will be there forever and spending a fortune just to solve glitches.

 

My issue is resolved, just needed the quick power cycle. Thanks Steve!

John

 

Glad to hear it Johnken.

I just want to say that this is a rare occurrence and the key clue was when Johnken said the needle was stumbling. This will not be the case for most of you.

The most common problems leading to erratic temperature readings are an intermittently sticking thermostat or a failing temperature sensor. They are far more common than the case here.
One should not hesitate to replace a suspected intermittently sticking thermostat because overheating on these engines can easily be catastrophic.