Did plenum fix and replaced 195 thermostat while at it. Had to replace both temp sensors as they fell apart with NAPA versions and now I'm reading 210 on gauge. Used teflon tape when installing sensor. Old thermostat/sensor read right on 200.

 

The sensor for the gauge (97 and older trucks) grounds thru the manifold, so, using the teflon tape might be interfering with that, which would give you an odd reading.

 

Wondered about that ..ideas on what to use? Other sensor had a dry red sealer already applied. Mine is a 1996 and runs great after Plenum repair...thanks for the help!

 

You could try twisting bare wire around the remaining brass head and threads, then grounding that wire. This will, at least temporarily, tell you if its the sending unit. Unless you really laid the tape on thick, the threads will cut through some of the tape and make contact.

 

They are pipe threads, so, they are tapered a bit. Just thread it in a bit more than snug, and it shouldn't leak. Don't use anything on the threads. The other sensor is a two-wire sensor, and it just modifies a reference signal, so, doesn't need to ground thru the engine.