Loud Fan Noise - E39 528it

[mistertripps]

Our wagon runs great, no fluid leaks on the garage floor or any other noticeable problems. However, when the A/C is on and you accelerate from a stop, there is a really loud knocking type noise from the engine compartment. It goes away as you get up to speed and doesn't happen at all if the A/C is turned off. Does this sound like the start of something bad or just something irritating that we shouldn't worry about?

[blackstig]

I would definitely look into that, what I would do is sit in the driveway with the A/C on and rev the engine as you would if you were picking up from a stop. It could be something like motormounts to where a piece of the fan is starting to tap a part of the body. If it's actual knock though like engine knock then you should look into getting your engine serviced. It may just be running bad fuel, I always run 93, but it could be that.

I'm not sure, I'm one of those weird people that have to "hear it" in order to say it may be something.

Hey, you're in Douglasville too, if you want we can meet up and I can look at it, I make no promises but two heads are usually better than one.

-Stig

[mistertripps]

I would definitely look into that, what I would do is sit in the driveway with the A/C on and rev the engine as you would if you were picking up from a stop. It could be something like motormounts to where a piece of the fan is starting to tap a part of the body. If it's actual knock though like engine knock then you should look into getting your engine serviced. It may just be running bad fuel, I always run 93, but it could be that.

I'm not sure, I'm one of those weird people that have to "hear it" in order to say it may be something.

Hey, you're in Douglasville too, if you want we can meet up and I can look at it, I make no promises but two heads are usually better than one.

-Stig

Thanks Stig - we may take you up on that. My wife wants to take it in to have it checked out, but I just wanted some "expert" opinions before taking it to the real experts. It really isn't an engine knocking like you get with bad fuel (we have been running 89). It sounds more like a fan that is just not turning exactly true.

[GCR]

Our wagon runs great, no fluid leaks on the garage floor or any other noticeable problems. However, when the A/C is on and you accelerate from a stop, there is a really loud knocking type noise from the engine compartment. It goes away as you get up to speed and doesn't happen at all if the A/C is turned off. Does this sound like the start of something bad or just something irritating that we shouldn't worry about?


A/C compressor going bad. We see a lot of them. Make sure your auxiliary fan is operating properly as a bad aux fan will raise pressures in the A/C system sufficiently to damage the compressor. There is a high pressure switch in the system that disengages the compressor when pressures exceed 375 psi, but operating just under that threshold for extended periods will damage the compressor. In other words, a new compressor won't live too long if the aux fan is bad..........

[e39driver]

However, when the A/C is on and you accelerate from a stop, there is a really loud knocking type noise from the engine compartment.

One of these two links may help:

http://www.bimmerboard.com/forums/posts/400697

http://www.540i6.com/finalstagereplacement.html

Good Luck . . .