Your 300SDL has a different type of engine temp. switch. It's a 3 pole switch, 1 pole is a common and the other 2 poles activate separate relays for low and high aux fan speeds. Your car also has aux fan switch in the A/C drier. See earlier posts.
As for the viscus fan clutch, when the engine is warm it should be almost "locked in" with the engine speed until 2000 - 2500 rpms.
If your engine runs that warm (105-110) while driving down the road at 40 -50 mph, then you have restriction in your cooling system. The most common restriction is the thermostat, then the radiator next.
If your engine runs 105-110 only at idle with the A/C on in traffic on a 95deg. day, check that your aux fan is running. Does it cool back down within a mile or two when you get moving again?
Give me more info as to what the circumstances are when your engine runs 105-110deg, and we'll go from there