Have a 1990 F150 with a 351 in it. All of a sudden the temp gauge on the dash isn't moving. Even if I drive for an hour or so it doesn't move. The truck is not overheating as far as I can tell. Looked at the fuses, but didn't see any that looked bad and even if one was it should have taken out more of the instruments I would guess. My Haynes book mentions a distribution panel which I can't seem to find so I'm also guessing that my year model didn't have it yet???

Ideas on the gauge? Could it be the thermostat itself or a short or???

Any help is welcome.

dp

 

I would first check to make sure your thermostat isn't stuck, then make sure your gauge is functional. Sometimes guages become faulty after awhile. Right now, I can't think of any other reasons why your temp gauge wouldn't budge. Then again, I'm not the tech. expert around here by any stretch of the imagination.

 

Couple of more questions based on the first response (thanks!):

- If the thermostat is stuck or busted in general, wouldn't the gauge still work???

- How to test the gauge itself without being an electrical engineer??

thanks, dp

 

Well, like I said, I'm no mechanic, but think of it this way, when you first start your truck in the morning, the temp gauge is all the way past the dash and stays there for a minute or so until your thermostat opens up. Then your needle will climb to the "m" or "a" and drop back down to the "n" or "o". If your thermostat is stuck, your gauge will just remain past the dash, even though your gauge works. Sorry I can't give you the technical description. As far as diagnosing the gauge, I'm going to need some backup on that one.

 

It is most likely a bad temp sensor, but there is also the possibility of the gauge beign mechanically bad or stuck. If you look in a repair manual it will give you a spec for the resistance of the temp sensor at different temperatures. You can check it that way. Sometimes you can also short or ground the wires going to the sensor to make the gauge read hot or cold.

Theres also the remote possiblity that both the guage and the sensor are working fine but there is a wiring problem in between.

-Jon

 

Next dumb question, where the heck is the temperature sensor? Don't see it in the manual.

thanks, dp

 

The temp. sensor is on the left side just aft of the distributor between the fuel rail and the intake manifold. It is not an uncommon problem for the gauge to go bad. I have heard of several people with this problem including myself. To test the gauge, unplug the sensor, look inside the plug and you'll see two contacts. If you run a wire from one contact to the other of the plug, basically shorting the plug, with the key on it should drive the temp gauge full hot. If it doesn't the gauge is bad, if it does the sending unit (temp. sensor) is probably is bad.

 

THANKS to all who responded. $4.51 and a temp sensor later the gauge is working fine. Saved me who knows how much in shop fees.....

THANKS AGAIN and keep up the help!

dp