How do I replace the temp sending unit on a 1982 gmc 305?

 

Unscrew it from the driver side of the engine by the front exhaust port. Careful, I think coolant will flow out when you do this, so have a new unit ready for installation.

Before you replace it though, look at this chart and grab your ohm meter and do some testing:


Put your positive lead on the end of the sensor, and the other on the block. The sensor grounds to the block. The circuit works by sending 12" volts through your gauge, and grounds it through that sensor, basically a thermal resistor, into the block. The hotter the coolant, the lower the ohms will be. The colder the coolant, the higher the ohms will be. I'd say run the truck up to running temperature, then grab the ohm meter and check to see what the sensor says the temperature should be.

If the reading on the senor is good compared to the chart, you have high resistance somewhere else in the circuit. I'd suggest looking into a chilton's manual from your library, or getting a Haynes manual from Autozone. Both will have wiring schematics to help you figure out the circuit a little bit better.

Good luck