the fan tested on a stopped engine is useless as the fluid enters the working chamber under gravity. The only way to test is to spin it up.

cold start test
fan engaged for 5 to 20 seconds then freewheels - good - stopping engine at this time would cause the fan to pinwheel to a stop.
fan has no engagement at all when dead cold on stopped engine and you can pinwheel it by hand - bad
noise from bearing - bad


hot test - engine temperature approximately 95 or 100C, hood closed after a drive - pop hood to test, fan should blow a gust of air on acceleration of engine. - good - at this point of time, shutting down the engine will stop the fan dead or about 1 blade pitch rotation.

hold engine at max pedal and see the fan decouple (start to freewheel) at above 3400 rpm - fan good.

no coupling when 95-100C - engine area blazing hot - bad clutch, most likely may also be bad radiator.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

The opposite is also true. If the clutch is always engaged, even when cold, it's bad.

And check that ALL fan blades are intact, with no cracks. I had to replace both in my 300D W123 due to a seized clutch (always "engaged") and a few cracks in one of the blades.



I think the 602/603 engine has a slighty different setup, the clutch may have only one center bolt. Make sure it's intact, and the bearings inside are not noisy or allowing the fan to wobble.

Technically true, but that mode of failure is extremely unlikely to result in overheating or other serious consequences, and also isn't very common.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

This occurs when the bearing siezes. Very common on BMW fans.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

It happened to my 300D. This resulted in overcooling, and it took longer to reach operating temp. Overcooling isn't good either.

Plus, at high speeds, the fan is always engaged. Not good for the engine either!