Bollinger

It's funny, a friend pointed out to me that 12V Audis can make the noise also.

But anyway, I heard this 740i going down the road. When he hit the gas, it made a ton of whooshing noise, like a tractor-trailer.

From what my friend told me, some cars (still) have a fan attached to the driveshaft. This fan is typically on a clutch (at least on German cars, I don't know about US) so that it can be designed to work well at 1,000RPMs and yet when the car starts turning 3,000RPMs the clutch is supposed to slip and keep the fan from turning too fast and making a ton of noise and wasting fuel.

If it binds up then the fan revs up as your engine does and your car gets really noisy when you rev it, like REALLY noisy. I could hear this 740i do it from about 80 yards away over moderate traffic.

My friend who told me about the problem had it happen on his 1997 or so A4.

Anyway, it seemed kind of funny to me. I also heard an A4 making a diesel kind of noise at the dealer when I took mine in for fuel senders. That car must have either slipped a timing belt or have zero lubrication to the valves. It sounded like a Freightliner when they parked it.

Wireless

all other gears I hear less fan/whooshing

Seattle Scott

The design does have some significant advantages over the 2.8 12V (and probably the newer V6s) fan system. More dependable, simpler, less costly, failure mode results in a whoosh sound and MAYBE the engine being too cool, water pump can't seize and take out the timing belt, no sensors, no switches, no way to get a dead battery (if the fan motor(s) stay on when the ignition is off).

I don't think you will see a design this good go away for a long time.

You could compare it to the simple single mast radio antenna on my truck and the three antenna, two amplifier/mixer system on my Audi.

Stu B

Was it a newer or older E38?

captainbilly

I believe those fans are controlled by a thermostat built into the fan hub. If the air coming through the radiator is cool then the thermostat lets the fan free-wheel, if the air is hot the thermostat causes the fan to be driven. Normally at high speed or any time the car is cool) there is enough air going through the radiator so that the air moving through it is cool and the fan is free-wheeling. This method has been used in many makes of cars for a long time.

I did notice this noise on my 740il and I also get it on my 2.7t when it's hot.

Bollinger

The current (about to be out) body style, but not the latest trim and such.

Chuck540MZ

Sounds like the normal operation of the temperature controlled clutch fan doing its job.

Bollinger

It is possible I guess, but although it was hot, it wasn't hot enough nor that car under enough stress to need to crank up the fan that much if it was working right.

TheBrit

I recently did a run down to London (about 140 miles at around 80mph) and when I got into the London traffic, every time I pulled away in 1st there was a loud whooshing sound from under the front end - it sounded like a hovercraft or something. Once I got onto some freely moving traffic again, it stopped. The water temperature guage never rose above 90C, but the oil temperature went up to about 110C in the stop-start traffic. External air temperature was in the region of 20C.