This has been discussed to great length on other forums. According to them, the M54 has low tension oil rings. Increasing crank case vacuum helps these rings seal, stopping oil consumption. Oil consumption seems to be hit or miss on M54s, but this has been a documented issue since they were first released. I'd wager that is why there is the extra capped vacuum port on the CCV and the corresponding capped port on the intake manifold. Funny enough, running a vacuum line from the CCV to the intake manifold (as shown in realoem) significantly helps, if not cures, the oil consumption issue.

^Josh did you do it on yours? Which one of the ports did you run it to? I really dont want to do the CCV job again since I only did it 2.5 years ago but this may be a good way to do it since I already upgraded to cold weather parts.

I replaced those small vac lines at the back of the manifold and the vac caps earlier this year.

It has been documented that this mod can stop oil consumption. Has it been documented if the practice is good or bad for the engine? Anybody checked if there are downsides elsewhere? Anybody know if this has been driven by saving money verses cost of rebuilding BMW system? Or, by someone that is a CCV 'expert'? What I read is it is a theory, according to, odds are, etc.

Not taking a position either way just pointing out there may be potholes on this road worth consideration.

The cold weather parts don't help that much in really cold weather. Moisture build-up freezes in the vacuum manifold instead of the CCV.

@bcredliner You do make a good point, it is a bit scary that most of the guys doing the mod don't really understand how either system works. Like I said earlier, in most cases there is a bit a luck/magic involved as well. ;)

It might be better, it's easy to innovate if you don't know it can't be done.

That is why when I do something about this, I am going to replicate a different stock system. M56 SULEV. One hopes the engineers that deployed it knew the answers to those questions...because it did get approved and implemented. I'm just going to copy them.

@lo-jack
It's best to inform yourself about how things work and know how you want to change them, not to try to copy. It might be the same engineers that designed the M54 CCCV ! What I am really curious about is why the crankcase needs to be completely closed in the first place? emmisions maybe ? to meet what spec? what is the reasoning ?

From the "Way too much info Department"
 

Closed crankcase venting systems (CCV) are a US Federal emissions requirements from the 70's as part of the requirements to capture the evaporation (venting) emissions (began in the late 60's for CA vehicles). They require a manufacturer to reduce the output of engine combustion vapors, gas evaporation, etc. The test is a vehicle in a plastic bag. Every year this capture requirement level was raised throughout the 80-90's. Before then everything was vented to the ground. Welcome to US DOT emissions regulations, now Euro and hence worldwide. See India and South America for non compliance. Gee I wonder if those vehicles had a different system due to no country mandated regulations required?

StepenVA, I think you mean "positive crankcase ventilation" PCV not CCV