When it gets to that temp, you should be able to hear the fan clutch pulling air through the radiator when the engine is revved up. Additionally, if you open the hood, and rev the engine up you should be able to feel the airflow from the mechanical cooling fan (keep your fingers clear).
Also, your car may be closer to overheating than your coolant temp gauge actually indicates. For an explanantion on how the gauge works on engines where it is controlled by the motornic control unit, see my thread
http://www.peachparts.com/shopforum/showthread.php?t=127687&highlight=thought+mercedes+real+coolant+temp+gauge
Also, check the fuse for the aux cooling fans and make sure they are working properly. On that engine, they are steplessly variable speed and they should start to come on at 95C and speed up if the engine gets hotter.