Revised OEM PCV and Crankcase Breather Tube

06F129101P Front Detail

In my current quest to return some parts back to OEM spec, I’ve recently purchased the latest revision PCV components.  The latest revision PCV valve is “P” with the part number 06F129101P.  There is also another revision of the rear breather tube, part number 06F103215B.  The valves in the latest revisions seem much stronger compared to my old “G” revision.  The check valves are now spring loaded instead of free moving.  I don’t know when they switched to the spring loaded valves because I completely skipped over the 2 or 3 other revisions.

06F129101P Valve Detail

If you’re wondering why I went back to stock, I wanted to remove the catchcan I’ve been running.  An intake manifold teardown by a forum member  revealed that catch cans do little to aid in preventing the intake valve deposits inherent to direct injection engines.  I have also been thinking about the lack of intake vacuum working on the crankcase.  In the catch can setups, vacuum is sourced from intake air moving over the rear breather tube exit.  I think it is a max of 3″ of mercury according to BSH and this occurs in the higher rpms under boost.  At lower rpms, actual vacuum may be much lower.  Too little flow or stagnant flow through the valve cover may allow the blow-by gasses to start forming deposits.  I’ve noticed a little grime building up around the oil cap area, despite the regular oil changes.  The accumulation of these blow by gasses can contaminate oil and deteriorate it much faster as well.  Another side effect of routing all gasses through the rear breather tube seems to be, ironically, more oil in the charge pipes.  If a recirculation type catch can does not catch all the vapors, the rest end up condensing in charge pipes and intercooler.  The stock system sends them directly to the intake manifold to be burned off.  The way the stock system works, it only reroutes vapors through the charge piping and intercooler under boost.  When I installed my throttle pipe, a good amount of oil came pouring out of the pipes.

06F103215B Check Valve Detail

Now oil vapor in the in the intake charge is detrimental to performance.  This is where a catch can does help.  Oil vapor can effectively reduce the octane level of the intake charge and lead to more knock, which would then decrease performance.  I haven’t noticed a performance difference since I switched back to the stock system but then again, my car isn’t exactly a horsepower monster.  It is a compromise situation but after many miles of thought, I’d rather have the stock system deal with the evacuation of the crankcase gasses.  The stock pcv system flows a lot and I don’t think some of the catch cans flow enough.

06F129101P Rear Detail

The stock pcv valves have not been models of reliability, which is one of the reasons catch catch cans have sold so well. Modified and stock cars alike can blow through them.  These newer parts are now several revisions deep and they seem to be much more robust pieces.  The rear check valve in the breather tube looks much better.  The front pcv check valves have a more positive engagement compared to the “G” revision I compared it to.  I guess only time will tell!


5 thoughts on “Revised OEM PCV and Crankcase Breather Tube

  1. Pingback: PCV Valve and Intake Manifold Motor Warranty Extension « markFive GTI

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  4. Hi
    Question about your rationale for reverting to the stock system…
    You talk about possibly insufficient vacuum to keep the contents of the head/valve cover from stagnating…
    How does the stock system change this? Yes, you get intake manifold vacuum, but when does this actually work? If it was sucking air through the engine via the rear breather you’d get crazy erratic idle… there’s no source for “fresh” air for this vacuum to cause the air to be less stagnant?

    • Hey there,
      It is true that there is no source for fresh air. The rear breather is closed when the intake manifold is under vacuum and that is what prevents the engine from idling erratically. There is quite a bit of blowby and if the pcv passages are blocked on this engine, it will find a way out, usually through the valve cover gasket. I cannot accurately say how much more vacuum you get out of stock system vs rerouting it through the rear as I have not tested it. I will say that BSH tested their setup and found 1-3″ of vacuum (max) from the rear port, but only once the system is in boost and there is a considerable amount of air flowing. Since we spend a lot of time off-boost (during cruise) and there is less air flowing through the intake, I can only assume that the actual amount of vacuum is less than what BSH had measured. The stock pcv applies a constant draw on the crankcase during off-boost and on-boost events. Volkswagen went through great lengths to design the system to keep blowby from accumulating in the crankcase. As you brought up, there is technically no fresh air being introduced to the system, but the unimpeded and vacuum assisted evacuation of the blowby gasses is what the system was designed to do.

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