Cooling fan howl

[Aidan]

I keep forgeting to ask about this, but I finally remembered (doh),, the cooling fan on my 940 D24TDic howls when the revs get up, the vicous coupling is not siezed and turns smoothly by hand but it does have a lot more resistance compared to my 740 B200. It keeps pace precisely with the engine up to about 3,750 rpm and then remains constant above 3,750 rpm. I'm in two minds about this. On the one hand it obviously moves a lot of air thru the intercooler which is good for the turbo, and thru the radiator which is good for the engine,,,, and it sounds brilliant when you floor it, it sounds like a Stuka dive bomber when you let it rip ,,, but I'm concerned about the possibility of a fan blade shearing off at those kind of engine speeds on a long run, plus obviously it robs a little bit of power turning it at those rpm's. Most cars I've owned with a vicous coupling fan I have rarely heard the fan turn, 99 per cent of the time they just spun fairly slowly unless things got really hot and then you heard it kick in, but after a couple of minutes it dropped out again, where as this one is almost like a fixed coupling fan. Is this normal for this engine or am I looking at a possible future coupling seizure? Any thoughts would be appreciated, thanks.

[casioqv]

Are you saying that the fan does not increase in rpms with the engine past 3,750, or that it does?

Rumor has it that the later D24TIC had the "tropical fan clutch" from the factory, which is a huge (and almost necessary) improvement in my opinion over the normal clutch. I have this clutch on my car and can hear it engage loudly and firmly, but only when the engine is warm (usually going uphill) and then it disengages again pretty quickly. On cars that still had the worn out non-tropical clutch I never notice them engage/disengage, they just seem lightly engaged all of the time.

[Aidan]

Originally Posted by casioqv

Are you saying that the fan does not increase in rpms with the engine past 3,750, or that it does?

Rumor has it that the later D24TIC had the "tropical fan clutch" from the factory, which is a huge (and almost necessary) improvement in my opinion over the normal clutch. I have this clutch on my car and can hear it engage loudly and firmly, but only when the engine is warm (usually going uphill) and then it disengages again pretty quickly. On cars that still had the worn out non-tropical clutch I never notice them engage/disengage, they just seem lightly engaged all of the time.

the fan does not increase speed much above 3,750 rpm, on full throttle acceleration in 1st gear it might go to roughly 4,000 rpm (wind resistance on the blades probably prevent it from turning any faster). It will do this with the engine hot or cold, it never disengages.

[casioqv]

I don't think the D24 can possibly rev high enough to destroy the plastic fan, even if the clutch were locked solid. It sounds like it's more or less working properly to me, but I suppose you could swap it out with a new one or a junkyard one and see if there's any difference.