I bought a 92 Z-28 and the temp gauge reads hot. Here is what I have done:

1. Changed sending unit. Still reads hot.
2. Installed new mechanical gauge and reads normal, about 190 degrees. The factory gauge still reads hot.
3. Changed factory gauge with another gauge and it still reads hot.
4. Checked the ohms on the sending unit, and it appears to be good.

I need help on this ASAP. I took the car to get smogged and it won't pass the visual inspection.

All help is welcome. Thanks!

 

Good troubleshooting, you covered a lot of ground before asking for advice. Kudos.

So it's not the sending unit, it's not the gauge. It must be in the wire. It seems to be grounded.

A good way to test it: disconnect the sensor wire and pull the instrument cluster from the dash. Now the dark green signal wire should have NOTHING attached to it. Put a test light clamp on 12V source and put the test light probe on the dark green wire. Perform this test in the dash AND ALSO in the engine compartment. If the wire is grounded, the light will light up.

FYI, the dark green wire for the temp gauge is the middle wire in the top row of the right connector (C1) in the dash.

Hope this helps.
Lou