my temp gauge had quit working for awhile and i finally got around to fixing it .. turned out it was the temp sensor .. since instaling the new sensor my guage will go from middle of normal to 3/4 back and fourth.. i have very hot heat so i dont know what it could be

 

did u replace temperature sensor or temperature sender unit they different, the sender unit it for ur gauge and sensor for computer.

 

replaced temp sensor and the gauage started to work again before it just stayed below the c mark

 

did u get all the air out from radiator. make sure its full. what year its ur truck?

 

96 with a 302

 

check ur radiator water make sure its full , and check conector at sender unit some time they get lose. do u have any water leaks?

 

dont know what a sender unit is or where it is had a leak but put radiator stop leak in it and it stopped but the gauage problem was goin on before i even flushed it and put the leak stop in it

 

As they start to fail, they inaccurately read on the cold side. Try not to keep referring to the sender as a sensor. It's kind of like fingernails on a chalk board to me, and confuses other people. Sounds like air in the cooling system. Burp the system. Possibly contributory are weak or bad seal radiator caps, or thermostats get wacky if they are exposed to an excessive or frequent overheats. Or a leak even less than a pin hole will catch up w/ you eventually.