I stumbled upon this thread the other day and I have been following it as I have just started to have a problem with similiar initial symptoms. It's not my intention to hi-jack the thread, but I figure if I can get some help without starting a new thread, all the better.

I have an '81 300 SD. When the car is moving the temperature is just above 80*. When I come to a stop, the temp was climbing to 110*. As soon as I started moving again it would drop back to around 80*

When the temp. got hight I jumped out to see if the small fan in front of the radiator (auxiliary fan?) was spinning. It wasn't..

When I got home I popped the hood, and to my surprise, the coolant reservoir was empty. When I first got this car a few months ago I checked all the fluids every other day as a precaution. I learned then that I could not keep the coolant level at the fill line on the reservoir because it would be pushed out of the overflow hose that is by the cap. The coolant would level out about an inch below the full line, or so I thought. Other than some drops of coolant exitiing the overflow hose, I cannot find any coolant leaks.

Where could the coolant be going?

Other than being rought at initial start up, the car runs like a champ.

Anyway, I refilled the coolant reservoir. Now I am not getting the car above the 80* mark. The small fan is still not turning on, but is it suppossed to at this temperature?

I saw the post by Sixto about the 3 pin thremo switch. I did a search for this and came up empty. I'm not sure if it even applies to my car, as I follow the wires from the fan, to an inline plug/connector and then into the bottom of the fuse box. I have no idea where they go at that point. I checked all of my fuses, and they test good. I don't know how to test the releys that are in the box.

Other than keeping a closer eye on the coolant level, can anyone offer any suggestions?

I would like to know where the coolant is going and I would like to figure out if my fan is good or not.

Thank you.