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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > N20, N26, B46, B48 Turbo Engine / Drivetrain / Exhaust Modifications > N20 catch can and positive crankcase pressure
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      06-14-2021, 06:08 PM   #1
Onlybimmers
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N20 catch can and positive crankcase pressure

My engine is running perfectly fine. Very short OCI's, self maintained, 54k. So when I open my oil fill cap I feel a pretty substantial amount of positive pressure. If I try to pour some oil on with engine rubbing it will blow it away and make a mess. No smoke or vapor. I figured it was fine but today I went to check on the Mishimoto catch can. In warm weather I get very minimal, in cold I get tons of mostly condensation and fuel/oil blow by. Here's my concern: when I pop off hoses to and from the catch can, the "In" coming from valve cover is bone dry and the "out" going into intake piping is wet/oily with blowby. The "out" does have the brass filter before exiting. Is it possible the "in" & "out" labeling is wrong? The hose to the intake should be dry and the hose from the valve cover should be oily. Also is it normal for a lot of positive pressure to be exciting from the oil fill cap? I've had the catch can for over a year, these aren't new symptoms. No codes. Should I just order a new oem hose and go back to factory ccv system?
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      06-14-2021, 10:27 PM   #2
Billfitz
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Never add oil with the engine running. There is outward pressure, which can spray oil all over. The pipe to the intake shouldn't be wet. That might indicate that the can is too hot for the gases to condense. Having the can mounted in the usual spot, which is near the exhaust manifold, can contribute to that in summer. I didn't put mine there for that reason. Here's mine:

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