I've got a 97 supercab 2wd 4.6 that has an annoying habit. If it runs over 2000 rpm for a few minutes, the temp gauge spikes. Turning the engine off immediately resets the guage. There is no evidence of the engine actually overheating. Ideas?

 

The temp sender is going bad or there is a short to ground somewhere in the harness. The temp sender has a negative temperature coeficient, that is, the higher the temp, the lower the resistance through the sensor element. A shorted-to-ground wire between the dash and the sensor would peg the indicator max hot.

The sensor is located at the front of the engine on the coolant crossover casting.