ehm. I think you have either a electrical cooling fan or a mechanical one controlled by a viscous clutch. If you have the latter the fan is loose and just slightly spins along with the engine until the air temperature reaches a certain level. Then the clutch engages and the fan follows the engine rpm. That's how it is on my 1990 300E (euro model). Again - if indeed you do have the mechanical visco fan, it is possible to do the following check - JUST BE CAREFUL WITH FINGERS!!! - when the engine is hot (>90C) and running, take e.g a piece of cardboard (something that will not break fan blades, but sturdy enough to give some resistance) and see if you can stop the fan with that. If you can, your clutch is dead and needs replacing.