52 pickup,
Another welcome. As a new guy you need to learn to use the search feature in the header. If you type in temp. or temperature gauge you will get a number of posts which deal with trouble shooting, repair, and calibration of this gauge.
As a sidebar, fuel and temp gauges (balanced coil type) work the same way. The senders are nothing but variable resistors. As the fuel level/temp goes up, the resistance goes down (usually).
A number of gearheads lurk here just waiting to pounce on a truck/car problem you have.
