tommo2

Hi,
I have a 2002 A6 (C5) with 2.0l petrol engine, engine code ALT.
It has been burning oil for a long time now, around 1 to 2 litres every 1000miles.
Engine rings have been replaced, valve guides and stem seals replaced but still as bad as ever.
Today I removed the PCV valve and noticed a huge amount of oil in the breather system.
The oil is in both vacuum lines, one into the air intake before the throttle body, the other towards the inlet manifold.
Seriously, there is a huge amount of oil here, so I assume this is where the oil is going.
There are no leaks from the engine.
Anyway, the pipe from the crankase is bone dry indicating that no oil is coming from the crankase breather. The part of the PCV that connects to the camshaft vent is where all the oil is at.
Is there any way to install a catch can here to stop the oil going into breather, or maybe even vent this part to atmosphere?

Thanks in advance guys.

Just Me

Sounds like your breakther valve is not working. It operates on differential pressure between the manifold and the crankcase. Without it, a PCV valve is nothing but a hose, and oil flows from high to low pressure. Appears that is what is occuring.

You replaced rings for no reason?

Who's your mechanic?

Grant

tester123

Quick question, is this "breather valve" present in 2001 A6 4.2 Quattro? A quick google image search on this gave mixed results. Does it look disc shaped with fitting on bottom and side?

Please take a look at my thread regarding the sound "PCV" valve is making and provide any input. Here: https://www.audiworld.com/forums/sho....php?t=2809324

Thanks!

Just Me

no clue. I understand the engineering of a PCV function. How its implemented is always something to be studied. But from what i have seen, on all cars, there are basically two approaches:

1. PCV valve with anti-flow valve ( its a ball in a race)
2. air-oil-separator which is basically a still - oil soaked air rises, oil falls, air continues out thorugh a semi-pervious membrane (porsche uses these)

I think all audis are PCV valves, and i think all PCV valves have the ball in race thingy inside

Grant

tommo2

Thanks for the reply grant. Yeah, maybe the pcv valve is shot, but i would have thought that it would suck oil up from the crankase breater, not the cam cover. Anyway, i will fit a new one and see how that goes.
The car had 150k miles , and was due a timing belt and valve seal replacement. The garage recommended replacing rings aswell while head was off, so basically it would be like a new engine. It was not too much extra so seemed like a good idea at the time. Seemend like a good investment.

Anyway, if the new pcv valve still lets oil from the cam cover into the inlet, is there any way to vent the cam cover to atmosphere without losing oil?

tommo2

This is the pcv valve i have:

http://img257.imageshack.us/img257/3...athervalve.jpg

Just Me

You dont want to vent it- that messes with vacuum and thus motor electronics.

Vacuum goes both directions, depending on manifold vacuum, which varies from zero to big.

The valve is open when vacuum is low, and closed when it is high.

Again, just the theory - you need to figger it out.

Grant

tommo2

Ok , thanks for that.
I think I have this pcv valve figured out. Both crancase vent and camshaft vent connect into one end. There opposite end is connected into air inlet pipe before the throttle body. There is a diaphragm in the middle which closes as the vacuum rises to reduce suction. Also, there is a small bypass hole which allows a small flow when the diaphragm is fully closed. Makes perfect sense.
Now, before this diaphragm is a small vacuum pipe connected down to the manifold. I guess this is for when the throttle is closed and there is very little vacuum in the air inlet pipe, but the manifold vacuum is large.
Now, can you confirm I have this correct?
Also, is there a fresh air supply to the crancase or is the vacuum just pulling the blowby gasses? I heard somewhere that the crankase vacuum in theory keeps the crankase at a slight vacuum which reduced wind resistance and improves efficiency. This may be nonsense, but it would suggest that indeed there is no air supply into crancase.

SloopJohnB@mac.com

If it honks like a PCV valve, it's a PCV valve.....LOL

I have a 2K4.2A6 and an 02S6...I've replaced the PCV valve twice with non-OEM parts...the first replacement around 140K when my wife couldn't stand the honking, the second around 160K...the second one is just barely honking.

tester123

I get what you are saying here but it doesn't seem to add up. Don't know if you read through that thread but, the old one had a torn diaphragm and I replaced it with new one.

My question is, why would the PCV valve make the noise? I suspect it is due to compensating / pulling outside air in. I'll agree that I don't understand the operation completely but, that's what I am thinking how it works. The old PCV was just letting air right through the torn diaphragm so, it was not making noise (provided that this condition of excessive vacuum existed prior to PCV replacement). Secondly, the suction valve is another component that is in question...

Not to hijack this thread any further, I request you and others to please read / reply to this thread: https://www.audiworld.com/forums/sho....php?t=2809324

Again, your input is very appreciated!

To the OP, thanks for your patience!