Take a broom handle to the fan while it is spinning - if the clutch is shot, you will easily be able to stop the blades. Just did this trick about a month ago on one of my cars and it worked - fan clutch was bad!

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280