Don't worry about the guage vs. your other cars. MB uses guages which tell the actual, current temperature of the engine. Many other makes use an "idiot guage" - it points at the same spot in the center of the range for any temperature from just above stone cold to just below boiling.

Your m104 isn't really overheating. That said, it does seem to be running warmer than most others under similar conditions.

How does running the a/c affect the temperature? It's quite normal for the dual fans to run when the a/c is on. Is the temperature lower and/or more consistent with the a/c running?

Does it largely heat up during stop & go, but cools down when moving? From your post I don't really understand what is happening.

A couple of very random ideas. Check the aux fans to be sure they are spinning the correct direction - the air should blow through the radiator. How is the fan clutch? It should be engaging when the engine reaches 100C, making for a very noticable roaring sound when accelerating away from a stop. Any idea on the condition of the waterpump? I've not heard of m104 pumps having problems with the impeller, but anything is possible, I suppose.

- JimY