why is my Mercedes s-class overheating

Number of things, coolant level low, sticking thermostat, air in the cooling system, water pump or plugged radiator, cracked head or bad head gasket. Obviously start with the simple things, my guess is with the thermostat.

Let me get out my crystal ball........ hmmmmm........ It appears that you thought you could own a Mercedes without having a real Mercedes mechanic service it regularly-

You mit need a new fan clutch