Why is the intake plenum engineered to allow oil to be sucked into the intake charge on the v35? This would appear to be an issue with emissions but also with the oil usage. During a recent R&R, I was very surprised to see this and absolutely positive from the indications of oil mist on the lower and upper plenums that the gasket/metal block are not sealing this area.

Thanks for the information.

Back in 1963 the EPA forced vehicles to close up crankcase vapor emission via the PCV requirement.
http://www.filtercouncil.org/techdata/tsbs/94-2R1.pdf
Every engine since then has directed crankcase vapors to the plenum.

Thin oil, weak piston rings things that cause excessive oil vaporization.

chasracer wrote:Why is the intake plenum engineered to allow oil to be sucked into the intake charge on the v35? This would appear to be an issue with emissions but also with the oil usage. During a recent R&R, I was very surprised to see this and absolutely positive from the indications of oil mist on the lower and upper plenums that the gasket/metal block are not sealing this area.

Oil vapor reclamation is part of a Hydrocarbon reduction method.

A fine oil mist does tend to cause a sticky tar around some parts of the intake runners. As dirty as the VQ gets the tailpipe emissions are never really effected. The cylinder operating temperature is high enough to vaporize any oil that makes its way in. You might want to replace the plugs after cleaning the intake.

The engines that used an EGR were much more likely to develop large carbon deposits that would impeded air flow and alter tailpipe emissions. Now there are no exhaust so you will actually notice the small amount of oil (it never really gets much worse than a certain amount, unless really neglected)

If you want to stop this install a catch can. There are several threads in the M forum (m-series-forum-fuga-forum.html ) that have pictures and installation directions. This will allow all of the air while adding a filter medium (that will require monitoring, which is why their not on from the factory).