[dbond]

To those who was wondering what's inside N52 oil separator here is a few pics I snapped while taking it apart. I wanted to see how serviceable it is and find a way to test it. The separator is original to my '06 325i (N52B30 engine) and 125k miles. Part 11617531423.
Upon postmortem examination it was determined the separator was in a great health but died from the autopsy
So, it's not serviceable. But it was in good shape after 9 years and 125k miles. It can be cleaned with carb cleaner and compressed air.
The separator was replaced while troubleshooting a vacuum leak that I thought was the result of damaging the separator with compressed air. Not the case, the leak was something else.
There is a rubber diaphragm that works as a valve between the vacuum side (manifold) and the engine. Strong vacuum closes the valve preventing too much negative pressure to the crankcase. If you have trouble opening oil filling neck due to vacuum the separator failure (diaphragm) is the prime suspect.

EDIT: Now that I think about it there is a very simple test to determine the diaphragm health. There is a nipple on top of the oil separator covered with a plastic cap. The nipple is visible from the top of the manifold between cyl. 5 and 6 intakes. Remove the cap and attach a tube snugly. Apply vacuum to the tube to see if there is a leak. No leak - the diaphragm is OK. The only other failure I can envision is if separator gets clogged. There is not much you can do, you have to take the separator out and clean it.

[rafa325]

Great info....

Unfortunately I changed the whole valve cover this week....

Thanks.

[lichtgelb]

Mine failed the vacuum test. I had rough erratic idle and it smoothed out after changing the entire oil separator system. I didn't do a post mortem but I thought about it.

[TeSmSp]

http://vanos-bmw.com/membrane-for-co...mw-11127552281