PCV or "donut" on valve cover

[rodpaslow]

I decided to cut it up and actually see what the function of it is.  I can't post the pictures now, I will later.

There's no gauze or anything related to actual oil separation.  It actually is almost opposite of a gasser pcv valve.  It has a very light compression spring in it with a diaphram similar to a boost/vacuum can diapham and it is almost at the top of the can.  If you have blow by or slight crankcase pressure it will keep the opening to the outlet open.  If for some reason the outlet to the can has a vacuum the valve shuts closed - the diaphram is pulled down against the spring and closes the opening to the outlet.  (I also would think if the vacuum pulling from this can is bigger than the blowby you have, the valve would be opening and closing often.  It doesn't have to move much to close the outlet off, maybe 1/8")

I think what vw was trying to do is not have a vacuum situation happening in the crankcase.  I'm not sure the reason for that.

I have purchased a new valve and will be installing it as soon as I receive it!

[rodpaslow]

These are the pics.  I think it's pretty important to have one, even if it doesn't do much to separate the oil from the air.

[rodpaslow]

By the way, I'd take a spare if someone wants to sell one cheap....(vw wants $100 cad new, paid $60 for online aftermarket)

[JamesT]

It acts as a one-way valve, keeping air flow moving constantly through the block and into the intake. It's also a flow restriction, which isn't as important on diesel engines, but critical on fuel injected gas engines. On gas engines, the crank fumes are introduced to the intake air after the MAF sensor, and without restriction, could cause a lean condition or rich condition depending on crank case contents. In diesels, it just slows the flow of oil vapours.

[745 turbogreasel]

...isn't as important on diesel engines, but critical on fuel injected gas engines. ... In diesels, it just slows the flow of oil vapours.

Maybe in an ideal world.  If you get a bad enough combustion chamber -crankcase leak, like a holed piston, it will blow enough oil up through the tube to send the engine into runaway and catastrophic failure.  The CCV is slammed shut by this excessive  pressure, cutting off the fuel (lube oil) to the motor, and may save parts of your motor, or save you from parts of the motor!

[rodpaslow]

I never thought about that, but if you had a runaway situation or something more catastrophic - like you mentioned, it's possible the vapours being pulled from the intake could (I say could) be large and this would shut the valve and  save the motor or definitely parts of it!  Works for me..

[bbob203]

im pretty sure mine is hollow.....

[rodpaslow]

That's what I thought with mine initially as I couldn't see the spring from either the inlet or outlet.  It could be though, I know in Canada, I think the only cars that got this through the mk2 years was the turbo diesel.  The NA has a different setup directly into the intake.

[rodpaslow]

I've got the new one installed and for some reason I'm still having problems with either it or the provent 200.  The car running highway speed doesn't use any oil, but as soon as your stopped at a light, you can see and smell blue smoke, and burning oil smell if wind is  blowing the exhaust back towards the car.  I've stopped at my house pulled the cover off the provent 200 and the smoke stops immediately.  The provent filter is new, not over 5000 kms on it. 

Has anyone else had a problem where they were stopped and the car was burning a slight bit of oil?  and only stopped or slow speed?