My 1991 300CE runs at 85-90C, a little warmer now with a new thermostat. Prior to this it seemed to run too cool, barely 80C. Then the thermostat failed in the closed position and I overheated and this subsequently led, I believe, to a failed head gasket.

A thermostat is cheap and easy to change.

glenmore
1991 300CE
2000 C280
1990 LS400