Positive Crankcase Ventilation: Description and Operation

Engine: 5.4 Liter V-12 Engine (M73)
MODELS: 750iL (E38), 850Ci (E31)


The M73 uses two new type crankcase ventilation valves which function similarly to the ones used in the updated M42 and all M60 engines. The oil vapors in the crankcase enter the oil/vapor separators incorporated in each cylinder head cover allowing the liquid oil to return to the crankcase and the oil vapors to be drawn into the intake manifolds via the crankcase ventilation valves. Since the crankcase ventilation valves are influenced by engine vacuum, the amount of valve opening is varied continually through all engine operating conditions. Under low engine vacuum conditions the valves are fully opened by spring pressure and with high engine vacuum conditions the valves are closed.

Crankshaft Ventilation Valve:

- Low vacuum = Fully open by spring pressure.
- High vacuum = Fully closed by influence of vacuum.

The amount of valve opening is varied continually through all engine operating conditions.

The new valves are mounted directly to the rear of each intake manifold. The crankcase gas inlet of the valve is connected to the cylinder head cover by a rubber grommet. The cylinder head cover is modified to accommodate the valve and includes an integrated oil/vapor separator.