Atmo vented catch can - normal behavior?

[CorvallisBMW]

I have an atmosphere-vented catch can on my m30 swap. I elected to do this instead of running the valve cover breather back in to the intake, as oil vapor effectively lowers your octane rating and could cause knock with the turbo setup.

I noticed that once the engine is warmed up, at idle a TON of vapor comes out of the breather on the catch can. It looks like my engine is on fire. Is this normal? I wouldn't expect oil vapor at a standard operating temp of ~190F, but it absolutely pours out. Oil was changed just a few thousand miles ago with Mobil1 15w-50, nothing else.

[TobyB]

No, wouldn't expect that, unless it's been sitting for a long time and it's water vapor steaming off...

Usually you get a bit of 'resonant' flow, but nothing visible.

t

[ak-]

Do a leakdown test :^(

[CorvallisBMW]

Hmmmmm OK, that's not good. I'll have to grab a leakdown tester and see what's up. I really, really, REALLY hope the super rich BS caused by the Miller system didn't wash down/score the cylinder walls :(

[MC Hammered]

I had that happen with my catch can setup venting to atmosphere in my Audi.

My fabricator ended up plumbing a line to the exhaust and using that with an inline flow restrictor to get a vacuum pull to suck the vapours out.

I fabbed up a solution using an oil separator to replace the catch can but never ended up installing it before I sold the car.