Yesterday my temp gauge started acting crazy. It all started when I drove over to a friends house. On the drive over the temp guage was fine and reading normal operating temp. When i got their I probably visited for a couple of hours so the engine was not running and cooling at this time. So I get in my truck to go home and turn the ignition on without starting the truck. The gauge immediately went all the way maxed out hot. Well knowing good and well the truck wasnt hot I went on to drive it home. On the way home it would intermediately read from normal operating temp to maxxed out hot like it was cutting in and out. now it is always reading hot, even when the truck has sat overnight and with just the ignition on and the engine not running. All fluids are at appropriate levels and the truck is running great like normal. what should i check first on this thing?

 

It might have a bare spot on the wire to the sending unit, causing it to ground out. If you have problems with mice it would be a good place to start.