Question about overheating ..300E

Recently I have purchased a 1990 300E at 75k and have put on 10k more since then.
The car seems to be running at 80-85C while driving on the freeway but the temp goes up in slow traffic and at idle speed. I usually see the indicator go around and above 100C. For instance if I make a quick stop at a parking lot and come back to restart my engine, indicator seems to be above 100C. It cools down as I start driving but it worries me that it gets this hot.

I have recently got a new radiator and had the cooling system checked for any potential leaks. (no leaks found). I am suspecting that the thermostat switch is on the fan might not be working thus preventing the fan to kick in (?)
I appreciate your suggestions.

I just purchased a 1989 300E and am experiencing the same problems you are having. Did you find out what the problem was?

I have a 92 300E, and it seems like the fan is not switching on at the correct temp. Try installing an manual fan switch.

I've just replaced a viscous fan on a 124 for that problem

I am having the same problem. I live in the Phoenix, AZ area where daytime temperatures in the summer can reach 115 deg F. I just had the cooling system overhauled with new radiator, thermostat and radiator cap at one of the local dealers and it still likes to climb into the 100 to 120 degC range when stopped in traffic. Although I have not checked to see if the fan is operating properly, are there any other possibilities? I have approximately 120k on the car.

Well after trying many things to get the temp to drop, I decided to take a look at the fuse box(this will be the first place to look next time) I found the fuse to the aux fan was burnt, it wasn't visible until I removed it. I replaced that fuse and a couple of other questionable ones. Since that day my 300 has not gone above 85-90c and that is driving all over downtown Phoenix......fast

In the aux fan circuit that turns the fan on whenever the air conditioning is running, there is a voltage dropping resistor. It turns out it was open on my 300E. Had it replaced and now the car runs much cooler.