I have a 1998 E320. Lately when I come to a stop and sit awhile, the temp gauge may climb from 80c to 90c. When I start driving, the temp goes back to 80c. Any suggestions??

 

Time to replace your fan clutch or thermostat in my opinion. Try to spin your fan blade with engine stoped and cold to see, if you can feel resistance in it. If it is free spinning, clutch is bad.

 

How free is free? When I spin it, it goes about a quarter revolution. Doesn't feel like a lot of resistance. I guess I started noticing this is when I stopped using the heater. Tonight I put on the defroster and the temp came back down. If there is a 190 (87c) thermostat, then where should the gauge be pointing?