My buddy is bringing his truck over tonight. The temp gauge when he first got the truck was not reading anything and sat at full cold for the 250 miles trip to home. a few days ago it pegged out at full hot where it sits now. He said the engine does not seem hot. seems random. Also has worked just fine once or twice. Is there a common problem for this? I'm going to check the wires? anything else to check?

 

Sounds like a sender wire shorted to ground.

 

Check the ground up on the grille support by the battery tray there should be two wires grounded to it, When this came loose it made my guage go absolutly crazy and made me think that it was scarry hot at times.