Anybody know how to diagnose a faulty temperature gauge?

[CountryDriven]

My temperature gauge on my truck moves spontaneously, like it has a mind of its own. It goes from C at start up, all the way to H in a second, back to C, repeats this process but as it warms up the it goes from the "normal" to H. After awhile of driving its mostly on H and rarely comes down. I've changed my temp.sender and thermostat twice now...whats up?

 

[Spott]

Looks like it's already been diagnosed as faulty to me. It's either the sensor or the gauge. The only other thing I can think of that would cause behavior like that would be an air pocket trapped around the sensor, which is pretty unlikely.

I'd hook a multimeter up to the wires from the sensor, in circuit, and watch the voltage readings as the truck warms up. If the meter shows erratic voltages, then the sensor is bad. If the meter shows voltages that steadily increase to a stable value, then the sensor is good and your gauge (or surrounding circuitry) is bad.

 

[CountryDriven]

alright, im gunna go out and do this

 

[drchristopher7]

there are two temperature sensors for the engine...a temp sensor and a temp sending unit...one its beneath the intake manifold by the oil filter, the other is right on the thermostat housing body. I changed both and seemed to do the fix. the temp sending unit is connected to a vacuum line(by oil filter), so if not that then you might have a small leak or electrical short somewhere, but most likely its the sensors and they get gummed up with old coolant and fail...hope this helps

 

[AllanD]

a common problem on gen1 and gen 3 trucks is the problem you are experiencing..

The typical root cause of a loose or corroded ground strap between the back of the
drivers side cylinder head and that is supposed to run to one of the wiper motor mounting studs.

that is where I'd focus my attention.

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