It helps to have 2 people involved with this test so you can really see how long it takes for the fan to stop free-wheeling.

When the engine is good and hot and you shut it off, the fan should stop spinning pretty quickly. When the motor is cold and you shut it off, the fan will continue to spin for awhile.

When it's hot the clutch "couples" or engages, hence the reason for the blade to stop spinning quickly. When it's cold, the coupling hasn't occurred and the blade free-wheels longer.

With the car good and warm, have someone sit in the drivers seat with the engine running. Pop the hood and focus on the fan. Have the driver turn off the ignition and watch the fan blade. If it stops rather quickly, you clutch is engaging and likely working as intended. If it free-wheels, it isn't.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"