83 300sd Water Temp Question
 

I have put in three different thermostats in my 83 300sd trying to get the water temperature somewhere in the 85-90 range.
The thing that gets me is that it will run in the upper 90's whether the ambient temp is hot or cold and it appears that the faster I go the higher the temp gets. I also put in a new sender along with the thermostats and these changes did nothing. I am in Louisiana so I don't use the heater alot but I have recently. I have noticed that with the heater on, the water temp will stay right in the 85-90 range. I turn the heater off and the temp will rise back up. This tells me that it could be my radiator cannot handle the load, and with the additional water cooling of the heater coil, the system can regulate the temp where it should be.
I need some suggestions on what ya'll think.
Thanks,
Rodney

I would also suspect the radiator if turning on the heater makes a noticeable difference. When I replaced my radiator in the 300D, the temperature dropped about 5C. I think I'm going to toss an new radiator in the 240D this spring, it always seems to run about 5-10C too high (and the PO was running green crap in it).

The radiator is probably plugged or restricted internally. You might try back washing the back of the radiator surface to remove years of bugs and other debris from the radiator face. Easier with the fan shroud out of the way. Also how old is the radiator cap? If weak, coolant temp will raise. Get a Mercedes brand new cap.

Thanks guys, I will try to clean the fins and flush it real good. If that don't work I will bite the bullet and get a new radiator.
Thanks,
Rodney

I got a nice new one for under $200.00. It made a big difference. I also did a citric acid flush which cleaned out a lot of junk. In fact it cleaned out whatever junk was keeping my old radiator from leaking, hence the new one!