Originally Posted by thook

Do you know where the coolant temp sensor is? If not, there's two sensors on the front of the motor.....more toward the pass side. The one on your right is the coolant sensor.....(not switch or sending unit). To test it, put in a pot of water and place the two probes of a DMM on either terminals. The resistance reading should be high as the water is cold, but then gradually lower as you heat the water.

You could test it on the vehicle if you figure out how to do it without pulling the connector. Pulling it, though, would cause the truck to run VERY poorly while waiting for it to warm up. So, I'd use the pot of water. It's easy enough.

Other thing....if the sensor has a lot of deposits on it, they can lose some of their sensitivity to temp changes. I've been able to clean coolant sensors and switches with good results. But, if it's simply gone bad, nothing will help and the truck just won't idle well and lack power. Oh.....and run quite rich.