I rebuilt one radiator that truely needed it. I replaced one thermostat that was probably just fine: twice. I replaced one water pump that was probably fine, but the bearings did feel "notchy."

None of that fixed the warm running problems I was having. The car would regularly register 230+ degrees. Sometimes under similar circumstances it would register ~195 degrees which I would be content with.

I was about to post a thread asking on advice for which flushing agent to use when I decided to check the connection for the temperature guage on the guage itself. As I was pulling the guages out of the dash, the termperature dropped 20 degrees, playing with the wires at the back would get it to swing ~40 degrees.

Now, my question: does anyone know how to run a wire from the guage sender directly to the guage... I ask because it does not look easy with the big round connector that seems to send the signal. Also, which of the 3-4 temperature senders are the one that goes to the guage?

Thank You.

PS- This is the 1979 300SD in my sig.

The temperature sensor for the gauge is on the left side of the engine, near the middle of the head, near the #2 and #3 glow plugs. You need a wiring diagram to figure out what wire color feeds the gauge so you can tie in at the cluster. BTW, do not disassemble the big round connector because all the wires will fall out. It's a real PITA to get them all back in the correct sockets, trust me on this. Also, a jump gauge may also be due to a bad ground connection. Do any of the other gauges (fuel) jump around? I fixed my jumpy gauges by running a separate ground wire from the instrument cluster.

What, you mean like the mechanical oil guage or the mechanical speedometer? All joking aside I haven't noticed the fuel guage jumping around, and I was already planning on running another ground, thanks for the input though.

Given the location of the guages and the location of the sender, I bet my DMM will make fast work of it.

That should work.