The temp gauge in my truck hasn`t been working correctly for the past couple of weeks, this morning when I started my truck the gauge went up to just below hot and stayed there, the truck was cold, after a few minutes it went down to the cold side of the gauge. other days the temp gauge will move all over the place when the truck is warm, my truck is not over heating at all, I think I have a bad sending unit, were is the sending unit located and how hard is it to change?, do I need to drain the coolant to change it?.

 

TTT

 

TTT