how to test temp sender

As is being discussed in another topic , my 91 caprice wagon over heated big time last summer. The needle on the temp gauge went out of site and has stayed pegged ever since. I have figured out that the temp sensor in the intake, that communicates with the ECM was ruined. I suspect that the same thing happened to the temp switch in the head, that works the gauge. How can I check the switch to see if that's the problem? Cross the two wires in the connector? I have tried unplugging the wires and nothing happens.

The sensor changes values with temperature. You can remove it (the water will leak out of the block unless you plug the hole with another one) and measure the output while heating it in a pot of hot water. The specs are in the FSM. I believe the resistance goes up with temperature, but I do not know the number off hand.

sounds like the gauge itself is buggered,..

Resistance is inversely proportional to temperature. IE resistance goes up as temperature goes down. You probably don't have to drop it in boiling water for a quick check -- if you know the outside temperature with a cold engine, you can check against the chart in the FSM.


With an engine temperature of 68°F, the sensor resistance should be 3520 ohms (3.52 Kilo ohms).

59°F is 4.45 Kohms

50°F is 5.67 Kohms

...

-15° is 21.45 Kohms

-40°F is 100.7 Kohms

If the resistance at the sensor seems OK, then check the resistance at the PCM between C25 and B16. It should be the same. Higher means resistance in a wire or connection, lower means something is shorted.