Temperature gauge?

More than likely it's a simple mechanical issue. If they're using the same type of gauges everyone else went to, it is a "stepper" motor with a pointer on it. A computer places the armature in a specific setting through four electromagnet coils. If something happens to make the gauge jump for an instant, and it goes over half-way around, the next time you start a cold engine that armature will go back to "cold", but it takes the shortest route, which can be clockwise. With speedometers and tachometers you simply drive or rev the engine more than half scale, then the pointer will find its way there, then follow the speed back down.

With a temperature gauge, if you have two separate temperature sensors yet, one for the Engine Computer and a different one for the gauge, the one with a single wire is for the gauge. You might be able to unplug it and ground that wire while the ignition switch is on. When you unground it, the gauge should go back down the right way.

You can remove the crystal and physically push the needle back to its proper position. Most scanners have a gauge test menu that commands the gauges to go to various positions. Doing that will bring all of them back down. Some vehicles have a test sequence that is initiated by pressing certain switches in the right order.

I would have it checked to see if the temp is really getting that high. Many shops use an infered temp gun to check temps. So call around and ask if one of the shops would be willing to check it for you to see if it is really getting that hot. If it is then I would check for coolant lose. If it isn't getting that hot then change the temp switch for the guage. Let me know what you find and we will go from there.