Ok I'm puzzled. I've had my truck few months now and love it. It's my first diesel I've personally owned. Now my problem is starting yesterday from a cold start temp gauge pegged out and fan stayed on with engine cold. I kept messing with it and unhooked batteries and restarted system and everything's went back to normal well made it bout 20 miles down Rd and temp pegged out again and fan stays running what would cause this? Any help would be appreciated thanks.