On my 2004 XKR the Temperature gauge goes to overheat in seconds. Haven't installed Steve's Real Gauge yet, haven't tackled the Dashboard in this car yet. Anyways currently Gauge operates in the lower half and then jumps to overheat. Engine seems not to be overheated. Turning Ignition off and restarting the car fixes the issue.
Any ideas what's going on here?
Cheers

 

Definitely double check the wiring to the Engine Coolant Sensor, it should be by the thermostat, front top and center of the engine (I have the XK8, and the XKR is a bit different). I believe a disconnected sensor give "infinite" temperature.

Separately, check the ECT over an OBDII code reader. A cheap ELM327 will do. See what the reading is. Operating temp should be in the 200 deg F range (say, 195 to 205). If the OBD temp is right, but the gauge is not, try a hard reset in case the stepper motor in the gauge needs a reset. FWIW, it should take a mile or 2 to get some warmth from the heater (gauge needle off the bottom by a bit). Full operating temp is quick, but might take, say, at least 5 miles. This is not instantaneous. A laser thermometer is also a good tool to have around and give you other clues.

Also, check and recheck the coolant level. The expansion tank should be full. Pump the radiator hoses to dislodge any bubbles. To be more complete, pull off the wheel well liner and check the recovery tank (should be, say, half full). Obviously, if the level is less than full, it is time to chase down any leak.

At this point, it looks like a computer logic issue. This is the part where people ask about the condition of the battery. Weak batteries have dropping voltage when the starter is engaged, and control modules hate that...

Best of luck, keep us posted.

 

Mendo, I also wonder if you may have a defective sensor. When you said no real sensor yet, did that mean you have one, just not installed?

if so it's got a variable resistor for calibration. Since the temp sensor just changes resistance due to temperature, you could use the calibration tool to test everything up stream from the sensor. As you increase/decrease resistance your OBDII will display different temperatures.

as I'm typing, I thought to myself: last time I looked, a temperature sensor was only a few dollars. It simply screws in with some teflon tape for sealing. Double check me on price, but it might be worth just replacing it.

I suppose you could measure the resistance from the sensor as the car warmed up if you wanted to prove the trouble.

either way I'm obviously hoping it's an easy cheap fix for you.

just checked. SNG Barrett has them for around $10. Be careful, a lot of other places are selling same thing for $30+.
John