Steve, I want to thank you for your insightful description of the workings of the CVV. There is no doubt in my mind about the workings of the lower part of the valve-the oil separator function is clear after your explanation. It almost seems like the top half of the valve was originally designed to supply vacuum at deceleration and idle to the FPR while it sucks blowby gasses into the intake at off idle engine speeds. When there is a strong intake manifold vacuum and the diaphragm closes, the vacuum is directed to the nipple which isn't even used by the M54. Off idle, the diaphragm opens and the blowby gasses get sucked into the intake because there is such a large volume of air moving through the intake. This reduced vacuum is not enough to suck the oil out of the sump, but, if with age, the diaphragm begins to fail, oil get sucked up the dipstick tube-at first increased oil consumption, then clouds of blue smoke and finally, perhaps hydrolock, if the vehicle owner is asleep. Hahaha! Not really!
So why did the BMW engineers design such a complicated and problematic system for PCV function. My 96 Ford Ranger pickup 4.0 has a $15 PCV valve that seems to take care of things just fine. My 85 Euro M6 has a tube on the dipstick that ends in a tiny orifice. A hose leads from the orifice
to a vacuum port on the intake manifold-PCV function handled. Do you think, perhaps, the German engineers of today are just a little compulsive???
Last edited by johnstern; 01-22-2012 at 08:07 AM.