Please help! 1994 F-150 with a 4.9L I-6. The temp gauge never seems to move and I live in Texas! I'd expect to see it rise a little. It does have a lower temp-rated t-stat than the stock one (can't remember the value off-hand, but it's also only about 14 months old). I do hear something that sounds like water boiling when I shut off the engine after driving around town in the heat with the A/C on.

Temp gauge not working or t-stat stuck? What do you think?

 

Take the wire off the block sender (above starter) and ground it for a few secs and see if the gauge goes up if it does then the sender is bad or the t-stat is setting wide open I bet on a bad sender. If it doesn't go up when grounded then there is either a circuit problem or gauge problem.

 

Does the upper radiator hose get hot? Even if the 'stat was stuck open, it would eventually warm up enough to see it on the guage.