Under 100 C is not necessarily too hot. Does it run steadily at temp? or creep up when climbing hills or fast running or what?
It could be a clogged radiator: After the car has warmed a bit (radiator is warm but not too hot) try feeling around and see if you have any cool spots. Telltale of a clogged radiator.
If the radiator is fairly old try using a hose and blast water from the fan side outwards. Could be a ton of bugs etc.
Try turning the heat on. The fan isn't so important but just the heater core in the loop will act as a secondary radiator. Does the temp go down?
Check the oil cooler as well. Is it hot?
What weight oil are you running?
Oh and does your Aux fan on the front of the radiator turn? On a prior car mine didn't and it turned out to be a mouse house built up under the blades. Cleaned it out (sorry mouse find another house) and not only did the Aux fan work again but the radiator also has more total area to dissipated heat with.
Keep us posted,
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)