I swapet motors a few years back too a 350 and never hooket up the temp gage . Just reacently hook'et my temp gage back up and it dose not read past 110 . I bought a new sending uint for a 305 because I had heard that they have a diferent resistences . Well thats not all that is diferent . The one in my 350 has a 13/16 s thred to the 305 has 5/8 s thred or somewhere close to that . The sending uint was 37 bucks and I can exchange it ,but witch one do I get . Can the one in the 350 just be no good , should I just get one of those . The sending uint in the block is from a 1980 3/4 ton pickup .

 

The sending unit size will depend on the year the head was cast more than the displacement. The sensors themselves are electrically identical.

 

Cool so the one that I have now is toast ? . Do sending units go bad or is thier any other thing that would make the temp gage not read past 110 . I belive the gage is good .