PCV Overpressure Issue
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A PCV (positive crankcase ventilation) overpressure issue occurs when the crankcase ventilation system fails to expel blow-by gases properly, allowing pressure to build inside the engine block. This excess pressure forces oil past seals and gaskets, most commonly the valve cover gasket. The problem often compounds when an old gasket meets high internal pressure, and it can cause a new gasket to fail prematurely if the pressure fault is not corrected first.
What it feels like
The most visible sign is oil leaking from around the valve cover, dripping onto the engine block, spark plug coils, or ground beneath the car. You may notice a burning oil smell during or after driving, especially under load or at higher RPMs. In some cases, oil migrating into spark plug wells can trigger misfires or rough idle. Smoke from the engine bay can occur if the leaking oil reaches hot exhaust manifold components. The leak may worsen over time or reappear shortly after you have the gasket replaced.
How to confirm it
- Start the engine and let it reach normal operating temperature. Use a hand-held vacuum gauge connected to an open crankcase breather line or dipstick tube opening. A healthy system should show steady vacuum of 3 to 8 inches of water. Excessive vacuum, or worse, positive pressure, indicates a PCV malfunction.
- Inspect the PCV valve (or integrated oil separator within the valve cover assembly) for blockage, carbon buildup, or mechanical failure. Follow your BMW service manual for the specific location and removal procedure for your engine code (N54, N55, N20, N26, F80/F82 M3/M4, etc.).
- Check the condition of hoses connected to the PCV or oil separator system. Look for cracks, disconnections, or kinked routing that would prevent blow-by gases from flowing to the intake manifold or catch can.
- If you have already replaced the valve cover gasket and the leak returns within a short period, re-measure crankcase pressure or vacuum before assuming the new gasket is defective. High pressure will destroy a new gasket quickly.
Parts that fix it
An aftermarket baffled oil catch can is a common solution to manage excessive crankcase pressure and protect your valve cover gasket from future damage.
Mishimoto Baffled Oil Catch Can - F8X M3/M4/M2 Competition by Mishimoto - $262.55. Direct fit for current-generation M3, M4, and M2 Competition models with integrated crankcase ventilation management.
Mishimoto Baffled Oil Catch Can for BMW F82 M4 by OEM - $262.55. Designed for F82 generation M4 with color-matched finish and OEM-style durability.
Mishimoto Baffled Oil Catch Can Kit - F80/F82 M3 & M4 by Mishimoto - $261.84. Complete kit for F80 M3 and F82 M4, includes hoses and hardware for full system installation.
Mishimoto Baffled Oil Catch Can for BMW N20 N26 CCV Side by Mishimoto - $238.95. Fits N20 and N26 turbo engines (328i, 335i, 340i) on the crankcase ventilation side of the system.
Mishimoto Baffled Oil Catch Can - N55 335i/135i 2011-2013 by Mishimoto - $230.95. Sized for naturally aspirated and single-turbo N55 models, prevents oil carryover to the intake tract.
Mishimoto Baffled Oil Catch Can - N54 CCV Side (2007–2010) by Mishimoto - $223.95. Targeted for twin-turbo N54 engines found in early 335i and 135i models, handles dual-turbo blow-by volumes.