Been driving the 97 C280 lately. Car has variable coolant temp. On a 70* F day, motor runs cold 170* F . on a 88* F day it runs 203 * F at road speed , 225 * F when sitting. I'm using the HVAC control to read temp. Time to change the thermostat as a precaution. It also might be time to change the fan clutch, if the idle is raised to 900 RPM, the temp drops.

Now that I think of it, my 97 SL320 runs 197 * F regardless of outside temp.