Crankcase Vent Pipe, Aftermarket - E36, E39, Z3, MZ3, M52, S52

This hose is part of the E36, E39, Z3 Crankcase Vent system on the M52 and S52 engines. It's a complex system with multiple rubber and plastic hoses running between the valve cover, oil separator valve, and the intake manifold. This particular line runs from the valve cover to the oil separator valve.

The system is responsible for separating oil from the air inside the engine and air intake. Liquid oil is returned to the oil pan while oil vapors are sent to the intake manifold to be burned up during the combustion cycle. It's also known as a PCV, CCV, oil separator, and a cyclonic separator system. Too much oil in the intake air lowers the effective fuel octane, leads to drivability issues, and causes increased emissions. A completely blocked CCV has the potential for very serious engine failure (hydrolock) if liquid oil ends up in the intake.

Signs of a failing CCV include: whistling noises in the intake, blueish smoke in the exhaust, high oil consumption, and thick white or yellow gunk under the oil cap. A failed crankcase vent hose is rarely the only thing wrong with the system and this is a good opportunity to evaluate the rest of the system. Chances are if oil sludge is present on the inside of any of the lines that the oil separator valve will also be coated with sludge.