I have a '78 300D. The car has started to overheat gradually. On Monday it started going into the 200-250 F zone. On Tuesday it was just as bad.
The symptoms: Car starts to gradually overheat while I am standing at a stop light. When I accelarate and start cruising at 30mph or more it cools back down.
Things I have done and checked:
I have checked the coolant level. It was OK but I added some water to top it off.
I have changed the fan clutch. I did that because the used one I installed was leaking fluid for the longest time. I figured it finally went and so I replaced it.

The car was O.K. yesterday, but today it is starting to overheat again when I am stopped at a light for more then half a minute.

NOTE: The only dealer open at that time had a leaking fan clutch. The clutch had a fluid spilled over the bottom of the part. Like a thick wax or fluid like silicon. I thought the clutch was bad so I asked for another one. The second clutch also had the fluid spilled. I thought it might be some sort of packing grease.
Am I wrong? Is the clutch faulty? Is there anything else that can be wrong?
Thanks in advance for any help and info!
Sorry about the long post.
Mark.