My coolant temp gauge never reads correctly. Sometimes it points straight down, sometimes what seems to be correct and then 20 minutes later somewhere else. I replaced tha gauge and the problem is the same. Do you think it is the coolant sending unit that is located on the left side of the engine by the manifold?
Tony

 

its worth a shot, they arew cheap

 

I would also check to make sure that the wire for the temp sending unit isn't shorting out in the engine bay.