I just discovered there is two types of fan clutch on W124 - my '88 230TE has an 'electro-mechanical' fan, which freewheels until heat sensor hits about 100C, then tries to take off (you can hold it with a carrot ticking over - not when its driving tho!!), but my '93 300TD has 'viscous' clutch which is push rather than spin at rest but spins up when the engine runs and seems to be blowing quite hard all the time. This type has a 'fluid coupling' some kind of 'silicon oil' - if this leaks the clutch won't drive the fan

- at least thats my current understanding!

Function? maybe to reduce shock loading on the fan? the electric one prevents overcooling by not driving til the temp is high enough I suppose

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cheers!!