Engine internals

Crankcase ventilation valve

Controls how crankcase gas returns to the intake.

Where it sits

In the cylinder-head cover or a connected separator assembly, depending on engine.

How it works

Pressure regulation and oil separation limit crankcase pressure and oil carried into the intake.

Think of it as

A pressure-managed breathing valve for the engine.

Symptoms when it fails

Whistling, oil leaks or rough idle can arise from ventilation leaks and need measured checks.

Lifespan

Usually condition-based rather than a routine replacement. Lubrication, overheating and the exact engine affect wear.

Repair cost

Internal-engine work is usually labor-intensive. Diagnosis and the engine code determine the repair scope.

The BMW angle

BMW crankcase-ventilation arrangements vary; some valves are integrated into a larger cover assembly.

Used in

BMW petrol and diesel engines; petrol-only systems are identified individually.

Sources
Same system

Engine internals

Engine blockHolds the cylinders and supports the engine’s rotating parts.Cylinder headCloses the cylinders and carries the valves that control breathing.Cylinder-head gasketSeals combustion pressure, oil and coolant between the block and head.PistonReceives combustion force and moves up and down inside a cylinder.Piston ringsSeal combustion gas and control the oil film on cylinder walls.Connecting rodTransfers piston force to the crankshaft.CrankshaftTurns the pistons’ back-and-forth motion into rotation.Crankshaft main bearingSupports the crankshaft on a controlled film of oil.