Hi Mike/Dr. Brad - not suggesting that recently filling the car up with non-MB fluid caused this problem. However, long term use of non-MB coolant and especially not changing the coolant on the prescribed schedule could lead to cooling system problems. Need to also make sure there isn't an air bubble in the system after the thermostat replacement. As to Water Wetter, my experience has been positive. My 240D used to creep up to 95+ or so during a hard hill climb and in stop and go traffic. After adding Water Wetter in conjunction with a cooling system service, my temp gauge is rock solid at about 85 now under all conditions. It's been that way now for at least ten years, although I do change the coolant every three years. Now, maybe the fact that the system was serviced at the time I added the Water Wetter comes into play, but I've heard similar stories from others too. Certainly I'd look at the coolant level, the concentration, the air flow, fan clutch, etc. There are lots of things that need to work right.

BTW, Water Wetter is available at most auto parts stores.

Len