Oil Separator Replacement/Cleaning Interval?

[heinzboehmer]

I refitted my CSL airbox today after getting my car smogged and I noticed the inside was coated in a thin film of oil. Nothing excessive, but definitely more than I would have expected from ~1.5 years of use.

The PCV/oil separator looks to be pretty gunked up inside, so I'm assuming this is part of the issue. Hard to take a picture, but this should give a good idea of the level of gunk I'm dealing with:



I was thinking of trying to clean it up with some throttle body cleaner, but thought it'd be a good idea to ask if this something people regularly replace/clean first.

Is this even something I should be worrying about? Will I be wasting my time trying to clean it instead of just buying a new one?

Hoping this is what's causing the oil build up in the intake, as it should be an easy fix.

Any help or tips appreciated!

[Tbonem3]

You can uninstall. I actually just came across a replacement kit on FCP yesterday. It was the separator and a couple of lines. Was like $130 iirc, so not bad if your is beyond cleaning.

I'd say it might be worth cleaning if airflow looks constricted.

In that pic, yours looks so, what do you think? I never bothered to look at mine.

$46 by itself

https://www.fcpeuro.com/products/bmw-crankcase-vent-valve-11157840446#fitment

[heinzboehmer]

Yeah the interior of it looks pretty disgusting. I guess I just don't understand how this specific part works on our cars to judge whether or not a clean will help to better separate the oil from the blow-by gases. My intuition tells me that it will, but I might be wrong.

I'll try cleaning it to see how much better I can make it. But yeah, new ones are fairly cheap, so I might end up just replacing it.

[bigjae46]

I'd clean it often. If the PCV clogs it will cause issues and oil leaks. The PCV is cheap enough to make not cleaning worth it.

[heinzboehmer]

I ended up replacing the whole unit, as it wasn't too expensive. I've driven maybe 100 miles and the inside of the new oil separator is fairly oily. Might need to take off the valve cover and make sure the return passage is clean, but so far so good.



Since I replaced the old one, I figured I would cut it open to see what it looks like inside:




Here's how I think this thing works:

• Oil vapors come in through the big opening (A) and climb up the long middle section.
• Any oil particles that hit the baffles will drip back down towards A and ultimately into the head.
• The oily vapors that do manage to make it past the baffles will then go into the spiral.
• Oil will be separated from air inside the spiral.
• The oil will drip down into B and the air will come out of C and get recirculated into the intake.
  • B leads to a passage that is cast into the valve cover and comes out its side (this is where the oil return line attaches). Passage highlighted below:

The hole in this passage does not have the biggest diameter, so it can probably get clogged pretty easily. If it gets clogged, it will result in oil accumulating in the oil separator and then being forced into the intake.

I plan on taking things apart and cleaning up that oil passage next. Will probably blow compressed air through it first, to see how much is coming out. Then clean it with brake cleaner and some pipe cleaners and blow more compressed air through it. Hoping this stops my airbox from getting all oily on the inside.

Here's a couple bonus close ups of the baffles and the spiral inside the oil separator:

[eacmen]

Might be a good candidate for a periodic ultrasonic bath.

[Will]

Thanks for dissecting it and sharing your findings.

[heinzboehmer]

Might be a good candidate for a periodic ultrasonic bath.

Yeah definitely. Would be super hard to clean otherwise.


Cleaned up the oil passage cast into the valve cover today. Started by experimenting on the old separator to see what would get rid of the sludge. Brake cleaner and some light rubbing seemed to work just fine:



Then I took off the beauty cover, oil separator and banjo bolt to clean. I used some pipe cleaners and brake cleaner to clean the passage as best as I could:



I found that the best way to do this was to feed the pipe cleaner through the side (the part with the threads) and pull it out the top of the valve cover. This is how much sludge came out of the passage on the first pass, without having sprayed any brake cleaner. That hole was completely clean beforehand:



Sprayed brake cleaner and ran pipe cleaners through a bunch more times. This is the best pic I could get of the end result (forgot to take before pics):



(Yes I did clean up the mess on the outside of the valve cover after I was done)

Also, I found this inside the banjo bolt when I took it off:




I think that some sludge got dislodged when I swapped in the new separator and got caught in the bolt. I did a valve adjustment not too long ago and don't remember seeing any sludge in it.

I'm hoping this clean helps the system work better.

[SteelGreyM]

thanks for sharing all this! I will have to clean mine next time it's off. In all honesty I never even think about how dirty this part gets..

[lemoose]

heinzboehmer Thinking about doing cleaning my passage and banjo bolt but I'm having a hard time visualizing where that banjo bolt is/comes from and looking and can't seem to find it in any of the parts diagrams. Where exactly is it?

EDIT: wait, is this the banjo bolt for the oil return line on the hot side of the engine?

[eacmen]

heinzboehmer Thinking about doing cleaning my passage and banjo bolt but I'm having a hard time visualizing where that banjo bolt is/comes from and looking and can't seem to find it in any of the parts diagrams. Where exactly is it?

Banjo bolt is on the exhaust side of the head.

[heinzboehmer]

EDIT: wait, is this the banjo bolt for the oil return line on the hot side of the engine?

Yep, that's the one

[zzyzx85]

If anyone else is going to replace the AOS, don't forgot to get a new o-ring (PN 11157830966) that goes on end "A" in heinzboehmer 's post above. I didn't replace mine (forgot to order it) and I think mine is leaking from there because I still smell oil whenever I drive the car hard.

[0-60motorsports]

I might need to inspect this too. What was the mileage on your car @heinzboehmer ?

[heinzboehmer]

I might need to inspect this too. What was the mileage on your car @heinzboehmer ?

Around 125k mi or so