My 1983 Mercedes 380SL seems to be running hotter than I like. It settles down at right at 100 C by the instrument panel temp gauge after running at highway speed for 10 minutes or so.
When I first got the car, it had a bum O2 sensor that made it run rich, but on the highway it'd run about 90 C. After I fixed the O2 sensor, it started running hotter. I replaced the thermostat (and the water pump, as a result), with the one called out in the factory service manual. That specification is for a thermostat that starts opening at 84 C and is fully open at 99 C.
I had the cooling system power-flushed and refilled a few days ago. Aside from that, about the only thing left to try is servicing the radiator. That'll be all kinds of no fun, since when I tried removing it last year while I had the water pump out, it wouldn't budge...
There's no oil in the coolant, or vice versa, and no white smoke out the tailpipe. I'm pretty sure everything's intact. It's just running hot. The question is: is that too hot? Or just right? Or hot but acceptable?