jumpy temps
 

My 85 300td is alsp hovering around 100c and jumping up into the red randomly, especially when I put on the head lights. '

Makes me think old deis is quite right.


Did he ever reply about the exact location?

BTW, I once tried replacing the sending unit and that wasn't it.

In your case it is an earthing problem, check your earth connection.

checked earth already
 

I have cleaned the earth at the engine compartment and at the tranny very well and that didn't help??
any ideas

Here is what I did once to make sure I had the correct temp. Pickup up a mechnical gauge and slide the sensor in the radiator hose and clamp it. Bring gauge to where you can see it. I drove the car that way for a few days until I knew that my car wasn't overheating and that it was just the guage not accurate.

Coleman Kelly
 

Your problem is most likely in the instrument cluster. You have a trace going bad. When turning on headlights and things go screwy is a good sign.