Ive got an 89 F-150 with a 351 in it. When it was cold out side my truck wouldn't warm up at all. So I replaced the thermostat and it would warm up to just past the C on the temp guage, but not into the "normal" area. Today I drove it when it was about 85 degrees outside and it did the same thing. When I got done driving it I let it run and stuck a candy thermometer in to the top of the radiator and it read 150 degrees. Please help this has got me stumped!

 

hmm, maybe your gauge cluster went bad.

 

Ya thats what I thought too, but the candy thermometer in the radiator read 150 degrees.

 

There are different types of thermometer that you can put in the engine! I changed mine after having the same problem. I think I had a 190F in it, but went to a higher performance thermometer at 180F to keep the engine slightly cooler. Is it possible you bought a lower temp thermometer?

 

Nope I checked that too. It's 195 I think. Im fairly good mechanicly and Im totally stumped.

 

maybe it's a bad t-stat...could be stuck in the open position.

 

I't's gotta be.

Leave the thermometer in the top of the radiator while the truck is running. The t-stat will start to open after 10 minutes or so, and the temp will rise suddenly. If this doesn't happen, the tstat is open. Look for flow in the radiator, too.

Take care,
-Chris