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BMW Crankcase diagram for Alpina B7

An engine crankcase breather hose is a primary component of an engine’s positive crankcase ventilation system, funneling pressurized air from the engine crankcase to the air/oil separator, also known as the PCV valve. The PCV valve, or air/oil separator, is designed to capture and remove oil vapors from the pressurized crankcase air, allowing them to drain back to the engine, while the pressurized air is fed to the intake side of the engine and utilized as part of normal combustion.

An engine develops positive crankcase pressure as a byproduct of the overall combustion process. Because of the combination of pressure, heat, and the air/oil-vapor mixture traveling to the PCV valve, the engine crankcase breather hose is a common failure item within the PCV system and is crucial to your car’s engine’s performance and emissions compliance.

• Cracks breaks, leaks: Over time, your engine crankcase breather hose can be easily damaged because of constant exposure to oil vapors, heat, and pressure from the engine. The engine oil can slowly break down the plastic or rubber materials, eventually causing an air leak. This can happen naturally, or because it is damaged from external contact.
• Broken connectors: Plastic can become brittle over time, especially when exposed to heat and oil, and it’s easy to break one of the securing clips or connectors for a PCV hose, either during removal or during other services.
• Broken or damaged hose: Soft rubber or brittle plastic, depending on the material of the hose, can result in an obvious hole or split in an engine crankcase breather hose, usually accompanied by one of the other faults listed below.
• Check Engine Light: Excessive unmetered air from a failed engine crankcase breather hose can result in a CEL for an air intake leak fault or other airflow-related diagnostic trouble codes.
• Misfire: A severe air intake leak can cause rough running and an engine misfire, a common side effect of a bad engine crankcase breather hose or PCV Valve
• Oil residue on or around the hose or adjacent components: As engine crankcase vapors escape from a faulty engine crankcase breather hose, the hose, engine block, and adjacent components are likely to become visibly soiled with oil residue and moisture. In the most severe cases, you will smell burning or burnt oil, and you may need to degrease the area to determine the exact cause of the oil residue.

About Genuine BMW

The original parts used by BMW to build your car are available as replacement parts under the “Genuine BMW” brand. When ordering a Genuine BMW part you are guaranteed to get the same part that you would pick up from your local dealerships part department. Genuine BMW parts have been built to BMW’s stringent standards and are the same quality of the original parts used to build your Ultimate Driving Machine.

You may not realize this, but the parts that make up your BMW are not necessarily manufactured by BMW. No cause for concern, as BMW designs the part, hires a manufacturer, and ensures its quality to you. In fact, many of these manufacturers have been making parts for BMW for decades. In our industry these manufacturers are called OEM (Original Equipment Manufacturers), and these are often brands you recognize, including Lemforder, ZF, Sachs, Bosch, Valeo, Zimmermann, Siemens VDO, Corteco, and more. Don’t be surprised to open that Genuine BMW parts box and find an OEM branded part inside, simply with the addition of a BMW logo.

Be sure to keep an eye out for OE tags on our product pages to quickly identify parts coming direct from OE manufacturers. That extra bit of insight could save you some serious money while shopping! Refer to our OE Academy for further information regarding the OE/OEM tags throughout the site.