NOTE: I figured I go ahead cross-post my project on this board as well to get more feedback. I was pointed to this board from elsewhere. This was done on an X3 35d, but the same should apply to the 335d. So here we go!!!
---------------------
PART 1
I've been at this for some time tinkering with the idea of reducing oil particles going through the intake via the crankcase breather. The issue is not really so much about oil consumption that is very well manageable at about 1 quart every 10K miles. The issue is actually about tar build up in the intake manifold resulting from the oil mist mixing with the soot from the HP EGR.
The crankcase breather is in the back of the valve cover (note: this picture from a slight different version of the M57 than what the 35d has, but the location is the same... More on the difference later)
I researched the history of BMW approach to this in the M57:
Design #1
The original solution had an actual filter in it. Through some research I found that the same design was used by Land Rover. While Land Rover had the filter as a maintenance item necessitating replacement every 20k-30k miles, BMW never did. This result in the filter clogging up resulting in high crankcase pressure, which ultimately caused issues with the turbo lubrication. That filter was very effective at removing oil particulates from the crankcase gasses, but required maintenance. I think at this as what the quintessence of the German Engineer designed before sales and marketing got involved... Here's how that filter looked like:
Design #2
Sales & marketing gets involved, so as opposed to making the filter a maintenance item (it's not terribly hard to get to it and replace it, but BMW has an ongoing effort, right or wrong that is, to cut down on maintenance requirements) they replaced the filter with a cyclonic separator. Conceptually it works like the Dyson vacuum cleaner: it is free flowing so there's nothing to clogs or maintain. It's not as effective as the filter so some diesel owners in Europe go back to the old design to cut back on oil going through the intake and make it maintenance item. Here's how it looks:
Design #3
Lastly it appears BMW has redesigned the valve cover all together which now incorporates the separator which is of the maintenance-free cyclonic type. My dad has a 325d with the M57 and although the crankcase breather assembly looks as the one above, once removed there's neither a filter nor a cyclonic separator, hence my deduction that the oil separation function is built into the valve cover design (that is unless sales & marketing took over engineering and decided to get rid of such nonsense and let the oil flow). Our X5 has slightly different breather assembly since the line that goes from the valve to the intake is not built into the valve cover. Nonetheless, there is no separator of any kind between the breather valve and the valve cover. Here's how our valve looks like:
--------------------------------------
So at the end of the day after a bit of homework I concluded that the initial design is very effective at removing oil particles, but not being maintenance-free prompted BMW to redesign the system. The result is a less effective yet maintenance-free solution. For me, as for others who have retrofitted the filter, the benefits of better oil separation outweighs the additional maintenance requirements, particularly since carbon (or better yet tar) build up has somewhat of a precedent in the US version of the M57 that allegedly has more aggressive EGR maps. This is particularly true on the 335d which, again speculations, not having a LP EGR (which is picked up after the DPF) recirculates only unfiltered gasses.
From what I observed soot is a very dry particles that makes me conclude that in and of itself soot doesn't build up excessively; it is soot mixed with oily vapors that builds up in a tar like obstructive crap
--------------------------------------
Unfortunately since our breather valve assembly is different design, the filter is not a simple drop in, just like it would in, for example, my dad's 325d. It just wouldn't fit.
So for the past couple of weeks I've been looking at way to fit an external oil separator (like the Mann+Hummel ProVent) but have yet to find an elegant and easy way to do it. Not to mention the annoyance of having oil collecting somewhere that makes the car looks like it has some sort of incontinence. And, last but not least, it is technically for "off road use only" in California which could result in failing visual inspection: so whatever I come up would need to be easily reversible so I can but it back to stock once inspection time comes...
Then I came across something in the TDI world called the "Old Navy CCV" (
CCV Mod - Page 2 - TDIClub Forums): it's basically a guy who has milled out of aluminum a CCV housing with a filter to remove the oil particulate. The TDI, even more so than our cars from what I've seen collect oil in the intake and inter-cooler. At the beginning I didn't give it too much thoughts as my head was elsewhere looking for a standalone separator.
But then I realized that the very same concept can work for us: what about adding some filtering media in our assembly?
There is a fair amount of room where some filtering media would fit very well, just like in the Old Navy CCV
Oil would get trapped in the medium and drain back. Every 20k or so mile would would remove 3 bolts, wash it with some gasoline and you're good to go.