My 300SDL is running at 100 most of the time - even a little hotter when climbing. There was a new thermostat installed, but the car continues to run at 100. The overflow radiator cap was replaced because the old cap had broken apart - rubber hard, spring broken. The new cap, purchased at Autozone, is supposedly rated at the same pressure as the original. The overflow was originally filled too high and I have been losing antifreeze out the overflow tube, but the coolant level is now where it should be. Three years ago, both the radiator and auxillary fan were replaced.
The air conditioner is fully charged with freon but only works intermittently. I was told I needed to replace the kick down relay and that would fix the problem. I purchased and installed a new relay, but it does not act any different. The compressor comes on for maybe a minute or two then switches off.