Sixto raises an important point. The fan system is intended to have a max RPM significantly lower than engine speed. Review the attached link for a discussion of fan motion; bear in mind their problem is different from yours, but the discussion is applicable if you've got a viscous-fluid fan drive.
Clutch Fan on 300D 124
'97 SL500, 40th anniversary edition
'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)
SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)