Positive Crankcase Ventilation: Description and Operation

BMW does not use a conventional PCV valve as you would expect to see on other vehicles.

The blow-by gasses which are produced during engine operation collect in the crankcase.






The crankcase is ventilated by a pressure-controlled system. The oil vapors in the crankcase enter a cyclone-type liquid/vapor separator which allows the liquid oil to return to the oil pan and the oil vapors to be drawn into the intake manifold via a pressure control valve.


The pressure control valve is attached to the intake manifold. It varies the pressure in the crankcase continuously depending on engine load and speed conditions. This prevents blue exhaust smoke and excessive oil consumption on deceleration due to peaking manifold vacuum, and assures reliable crankcase venting during all other engine operating conditions.