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Repair Summary
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.
See all vehicles this article applies to
E60 5 Series M5
E60 5 Series 523Li
E60 5 Series 550i
E60 5 Series 545i
E60 5 Series 540i
E60 5 Series 535d
E60 5 Series 530xi
E60 5 Series 530xd
E60 5 Series 530Li
E60 5 Series 530i
E60 5 Series 530d
E60 5 Series 525i
E60 5 Series 525xi
E60 5 Series 525Li
E60 5 Series 525d
E60 5 Series 523i
E60 5 Series 520i
E60 5 Series 520d
A BMW N52 crankcase ventilation repair may be needed to help cure a rough idle or burnt oil smell emanating from the engine compartment.
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.
View the detailed parts diagram for this repair.
Includes detailed part diagrams, part numbers and links to purchase all of the required components needed to complete this repair.
Before starting this repair, you must have the following required parts.
BMW N52 engine
The crankcase return pipe is notoriously difficult to remove without breaking, especially in older vehicles. Avoid vacuum leaks by purchasing a new vent pipe before starting this repair.
All N52 six-cylinder engines
The crankcase vent hose should be replaced when doing this repair. Since they are made of plastic, they are prone to breaking during disassembly.
N52 Engine
The oil separator valve gets clogged with oil and debris over time and must be replaced to avoid a rough idle and poor fuel economy.
N52 Engine
The vent hose runs from the oil separator valve to the bottom of the intake manifold. Like the other pipes comprising the crankcase breathing system, it is plastic and will crack over time, creating a nasty vacuum leak underneath the intake manifold.
Section 1 - Intake manifold removal
As discussed above, the intake manifold must be removed from the engine in order to service the crankcase venting system. The oil separator is mounted to the bottom of the manifold and cannot be accessed any other way.- For complete instructions on removing the intake manifold for this repair, please see our article BMW N52 Intake Manifold Removal – 1,3,5,6,7,X1,X3,X5,Z4 6 Cyl. for detailed instructions.
Section 2 - Removing the oil separation valve
Once the intake manifold is removed from the vehicle, replacing the oil separation valve and its associated plumbing is fairly simple. Please be aware that you will most likely spill some oil into the intake manifold when removing the separator valve causing the engine to smoke when it is restarted after the repair...this is totally normal. The smoke will disappear after a few minutes.- Lay the intake manifold on a clean bench. locate and identify the oil separation valve on the underside of the manifold.
- Unplug the electrical heater wires for the oil separator, crankcase vent, and return pipes.
- Using a T27 torx bit, remove the screws anchoring the wiring harness bracket to the oil separator.
- Remove the final screw anchoring the oil separator valve to the manifold.
- Disconnect the vent pipe from the bottom of the intake manifold.
- Remove the oil separator and vent pipes from the intake manifold.
Section 3 - Reassembly
Use the old oil separation valve as a guide to assembling the new valve. Make sure all of the new hoses snap firmly in place. A loose hose will cause a vacuum leak requiring the manifold to be removed from the vehicle again. Exercise care when reinstalling the intake manifold to avoid breaking any of the new vent hoses.BMW N52 Crankcase Ventilation Repair Finished
