The crankcase ventilation system in N52 six-cylinder engine is a common source of vacuum leaks and the top cause of rough idling in many BMW models. This article gives detailed instructions on replacing the oil separator valve, crankcase vent hose, and crankcase return pipe in a BMW vehicle with the N52 6 cylinder engine. Even though we used a 2006 530xi to perform this repair, this article can be applied to any vehicle with the N52 engine including most 2004-2013 1, 3, 5, 6, 7, X1, X3, X5, and Z4 series 6 cylinder models with minor modifications to the repair steps.
The crankcase ventilation system in the BMW N52 six-cylinder engine is comprised of the oil separator valve and a network of plastic piping underneath the intake manifold. Its job is to vent escaped gases (also known as "blow-by gases") that accumulate inside the engine block as a byproduct of combustion. If these gases are not vented out of the engine block they will produce excessive pressure inside of the motor. This excessive pressure build-up can be devastating, potentially blowing out gaskets and seals and causing catastrophic damage to the engine.
As blow-by gases accumulate inside the N52 engine, they are channeled out of the cylinder head via the crankcase ventilation hose to the oil separator valve. The oil separator valve removes any liquid engine oil residue from the combustion vapor and sends it back to the oil pan via the return pipe. The vapors are funneled out of the oil separator via another plastic return pipe back into the intake manifold so they can be recycled.
The BMW N52 crankcase ventilation system is a notorious cause of rough idling engines due to vacuum leaks. Time and the brutal heat environment inside the engine compartment can cause the plastic vent piping to become brittle and crack, leaving nasty vacuum leaks underneath the intake manifold. It is not uncommon for older plastic pipes to rupture or crack when the vehicle suffers a hard jolt, like those incurred from hitting a pothole or curb.
Over time, the oil separation valve can become clogged causing a burnt oil smell to emanate from the engine compartment. Replacing the BMW N52 crankcase ventilation system requires removing the intake manifold...there is no other way to access it. For more information on removing the intake manifold from your N52 engine, please see our article BMW N52 Intake Manifold Removal – 1,3,5,6,7,X1,X3,X5,Z4 6 Cyl.
for detailed instructions.