As part of my SLS rebuild attempt, I removed the viscus fan. And I did not reinstall it. Its winter up here and the electric fans will kick in at 110 just in case. It normally runs at 75 in town and 65 or so highway this time of year. And that did not change much since I only got to 80 in town.

Anyway, it may be physiological but it sure feels like the car has much better throttle response and a lot more kick.

I am not sure how much horsepower is produced at 1000 RPM, but it cant be much. And I would guess the fan sucks at least 20HP. Since the 20 or so HP wold be the same at 5000 RPM or 1000 RPM, I would suspect at low RPM its a great hinderance.

Anyone have some actual numbers? After a trip out of town I feel safe running without the fan for the winter. Two reasons, faster heat up and I think my viscus fan is faulty. I can not hold the fan at idle like I can in other cars, its seems like the clutch is mostly engaged full-time, although if I rev it lots I can tell when it fully engages.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car