How loud is your cooling fan? - The Unofficial BMW M5 Messageboard (m5board.com)

bimmernut1 · 2nd August 2008, 07:21

Here's the deal. For two years my car has run at slightly below 210 degF, right near midpoint. Recently my fan belt broke and was replaced. Now the car consistently runs cooler than it did, even during the most hot and humid period we've had in years. It's about a 1/4 section lower than original.

But, the cooling fan noise is now very pronounced under acceleration and the frequency is in line with the rpm. Almost sounds like someone slipped in a supercharger when I wasn't looking. Unfortunately the additional HP is not there to match the sound. The fan sound now is almost as pronounced as the engine sound.

The dealer kept the car two days, drove it and said it's the aux fan and there's no problem at all. My question is whether I had a problem before and now the car is sounding like it is suppose to; or whether there is indeed a problem that is causing the difference in pitch? Is there a way I can confirm it is indeed the aux fan making the difference in pitch?

HOVO · 2nd August 2008, 08:20

well i can tell you that the aux fan is pretty load, whenever I turn on the A/C, the fans starts, the higher the ac setting is, the loader the noise gets.. sometimes its really bad if the A/C is blasting, I can hear it inside the car but people have stopped me and asked me what the turbine noise is in the car. also ive seen other people have this problem of the fan being really load.

bottom line, get used to it. aux fans are really load

EricM5 · 2nd August 2008, 16:42

I have the same. The fan turns faster when the engine makes more rpm's.
My Jaguar XJR did the same thing, but did have a supercharger.

I haven't tested it with or without AC on or whatever. But I'll figure it out tonight

SSense · 2nd August 2008, 17:11

Its totally normal for the fan to be loud, when the A/C is on it rotates at its max speed, which keeps it loud.

Vason · 2nd August 2008, 22:04

I've had a few aux fan issues in the past and I can for certainty tell you all is normal. At times I wish it wasn't so loud but I have gotten used to it.

bimmernut1 · 4th August 2008, 02:56

Thanks guys. I'll just try to ignore it. I just found it strange that ithe car decided to get loud after 2 years. Like other enthusiasts, I tend to pay close attention to the sounds my car makes.

RemBrant · 4th August 2008, 08:46

I'd be checking the fan clutch on the main cooling fan. You should be able to turn it by hand with the engine off/cool with minor resistance. If the fan clutch is starting to go it will be very stiff to turn the fan, and it will whine up to a certain RPM, which will climb as it degrades, until it doesn't disengage at all. There have been several members who have had the plastic fan explode due to overrevving, and high RPM and do major damage to the enginebay, hood, components. All have commented on the whining sound, or turbine sound before it happened.

Also if the clutch is not disengaging it will be constantly turning at whatever RPM the engine is at and cooling which may explain the lower overall temps.

I replaced my fan clutch in about 15 minutes with an exact replacement clutch. Before I changed it it would whine to about 4500-5000rpm before kicking out. After I replaced it whine goes to a much more sensible 3000rpm, and only when it's 20+C outside.

Just some thoughts...

gsfent · 4th August 2008, 16:59

Quote:

Originally Posted by bimmernut1

Recently my fan belt broke and was replaced. Now the car consistently runs cooler than it did, even during the most hot and humid period we've had in years. It's about a 1/4 section lower than original.

But, the cooling fan noise is now very pronounced under acceleration and the frequency is in line with the rpm. Almost sounds like someone slipped in a supercharger when I wasn't looking?

I woud also check the tension on the fan belt, make sure it is not too tight.
Regards,
Jerry

ard · 4th August 2008, 18:47

1. When a thermostat fails it can stick OPEN and you will run cooler.

2. As mentioned by ONE poster, a failing fan clutch will allow the fan to run at engine rpm (it is supposed to slip at high rpm so it will run slower). If locked to engine RPM it can explode, taking oit hoses AND your hood. Search...

A

bimmernut1 · 6th August 2008, 00:48

Thanks for the most recent suggestions. I'll specifically take a look at the fan clutch when I return. I do remember it being hard to move but I'll pay closer attention when I retest it. I'll also check the thermostat and belt tension.

My gut feeling was that something is different but I just could not put my finger on the problem. At least I have some items to check now.