JaL3

Found a super clean but high mileage A8L with the 4.2 BAR V8 for reasonable price so I went to see it and took it for a test drive.

Before driving it though, after idling a couple of minutes, popped the hood and heard this whining sound, kinda like a high rpm fan.

Does this sound normal to you guys?

KnappAttack

Sounds like a blown oil separator diaphragm. If the sound goes away when you pull the oil cap off, that's what it is. The cap will be under very high vacuum too.

JaL3

Thanks! I'll check that when I go back to pull the fault codes and haggle. Changing the separator should not be too hard on the 4.2, I hope..

I did notice a bit of blackish smoke coming off the tail pipes when the owner started it, I'm guessing this could be related to the busted separator?

ppinto1

It could be the EGR valve. Mine sounded similar, but higher pitched - almost like a screeching belt.

JaL3

Bought the car, took out the PCV valve and can confirm, the diaphragm is busted.

ppinto1

LOL. I meant PCV.