BMW E46/E90/E91/E81/E83 X3 & Z4 N42/N46 Replacement Crankcase Ventilation Oil Separator Valve & Breather Hose Kit – Restore Proper Crankcase Pressure, Reduce Oil Consumption & Prevent Vacuum Leaks | Replaces Part No. 11157513903

Restore proper crankcase ventilation and help prevent unwanted vacuum leaks with this replacement crankcase breather valve and oil separator hose kit designed for select BMW 1 Series, 3 Series, X3, and Z4 vehicles equipped with N42 and N46 four-cylinder gasoline engines. The crankcase ventilation system, commonly referred to as the PCV or CCV system, plays an essential role in regulating internal engine pressure, separating oil mist from combustion blow-by gases, and directing crankcase vapors back into the engine's intake system. Maintaining properly functioning ventilation components helps support stable engine idling, reduce excessive oil carryover, and protect important engine seals and gaskets from abnormal crankcase pressure.

As factory crankcase ventilation components age, prolonged exposure to engine heat, oil vapors, pressure fluctuations, and repeated heating and cooling cycles can cause plastic hoses to become brittle, sealing connections to deteriorate, and internal ventilation passages to accumulate oil deposits. The pressure-regulating valve may also develop problems that interfere with its ability to maintain the intended crankcase vacuum. Common symptoms include rough idling, whistling or hissing noises, increased engine oil consumption, oil residue inside the intake system, visible oil leaks around engine seals, and engine fault codes associated with unmetered air entering the intake system.

This replacement crankcase ventilation kit is intended to restore the original ventilation arrangement by addressing deteriorated oil separator and breather hose components. The oil separator helps remove suspended oil droplets from crankcase gases before those gases are returned to the intake system, while the associated ventilation hoses provide the necessary connections between the engine and its crankcase breathing circuit. Replacing damaged or restricted components can help restore proper ventilation flow, reduce unwanted air leaks, and support normal crankcase pressure regulation when the original components are responsible for the problem.

Designed around the BMW crankcase ventilation component associated with part number 11157513903, this replacement kit provides a factory-style maintenance solution for compatible N42 and N46 engine configurations. The ventilation system relies on correctly matched components, secure hose connections, and properly sealed fittings to function as intended. Incorrect hose routing, damaged seals, or mismatched ventilation components can interfere with crankcase pressure regulation and create additional intake-related problems. Proper fitment verification is therefore essential before installation.

For aging BMW vehicles equipped with N42 and N46 engines, servicing the crankcase ventilation system is an important part of preventive engine maintenance. These engines depend on effective oil separation and controlled crankcase ventilation to manage blow-by gases and maintain appropriate internal pressure. Replacing deteriorated ventilation components before they cause substantial air leaks or pressure-related problems can help preserve engine drivability, reduce unnecessary oil consumption, and contribute to long-term engine reliability.

Key Features

• BMW N42/N46 Four-Cylinder Engine Compatibility: Intended for select BMW E46, E81, E83, E90, E91, and Z4 applications equipped with compatible N42 and N46 gasoline engines using the corresponding crankcase ventilation configuration.

• Crankcase Ventilation System Maintenance Kit: Designed to address the oil separator valve and associated breather hose connections, helping restore the intended crankcase ventilation pathway when the supplied components match the vehicle's original system.

• Restores Proper Crankcase Pressure Regulation: Supports the controlled movement of combustion blow-by gases through the crankcase ventilation circuit, helping prevent abnormal pressure conditions caused by malfunctioning or restricted components.

• Supports Effective Oil Separation: The corresponding oil separator helps separate suspended oil droplets from crankcase gases, reducing unnecessary oil carryover into the engine's intake system.

• Helps Prevent Vacuum Leaks: Replacing cracked, brittle, or improperly sealed breather hoses can eliminate unmetered air leaks originating from deteriorated crankcase ventilation connections.

• Supports Stable Engine Idling: Correcting ventilation-related air leaks may help reduce rough idling, fluctuating engine speed, and engine hesitation when the original PCV components are responsible.

• Helps Reduce Excessive Oil Consumption: Restoring effective oil separation and crankcase ventilation may reduce oil consumption associated with abnormal crankcase pressure or excessive oil mist entering the intake system.

• Helps Protect Engine Seals and Gaskets: Maintaining appropriate crankcase pressure can reduce unnecessary stress on the valve cover gasket, crankshaft seals, and other engine sealing locations.

• Factory-Style Replacement Configuration: Intended to maintain the original BMW ventilation system layout, hose routing, and connection arrangement when installed on a compatible engine.

• Important Preventive Engine Maintenance: Replacing deteriorated oil separator and breather hose components can help reduce recurring vacuum leaks, oil vapor contamination, and crankcase pressure problems.

Restore the intended crankcase ventilation performance of your BMW with a replacement oil separator valve and breather hose kit designed to support proper ventilation flow and oil separation. Replacing aging components can help reduce unwanted vacuum leaks, improve idle quality when ventilation faults are present, and minimize pressure-related oil leakage. For older BMW N42 and N46 engines, maintaining the crankcase ventilation system is an important step toward preserving dependable engine operation and long-term reliability.

FITMENT: BMW 1 Series, 3 Series, X3 & Z4 – N42/N46 Engines

This crankcase ventilation kit is intended for select BMW four-cylinder gasoline applications. However, the fitment of 11157513903 alone must be distinguished from the fitment of a complete oil separator and hose kit.

BMW identifies part number 11157513903 as a crankcase breather hose/return pipe, not the oil separator valve itself. BMW's official catalog confirms this part for E46 N42/N46 applications. Broader aftermarket repair kits containing this hose and additional ventilation components are advertised for other BMW platforms, but the complete kit's contents must match each vehicle's ventilation configuration. BMW Shop

BMW E46 3 Series Sedan (Approximately 2001–2005)

• BMW E46 316i – N42 1.8L Engine
• BMW E46 316i – N46 1.8L Engine
• BMW E46 318i – N42 2.0L Engine
• BMW E46 318i – N46 2.0L Engine

BMW E46 3 Series Touring (Approximately 2001–2005)

• BMW E46 316i Touring – N42 Engine
• BMW E46 316i Touring – N46 Engine
• BMW E46 318i Touring – N42 Engine
• BMW E46 318i Touring – N46 Engine

BMW E46 3 Series Coupe (Approximately 2001–2006)

• BMW E46 318Ci – N42 2.0L Engine
• BMW E46 318Ci – N46 2.0L Engine

BMW E46 3 Series Convertible (Approximately 2001–2006)

• BMW E46 318Ci Convertible – N42 Engine
• BMW E46 318Ci Convertible – N46 Engine

BMW E46 3 Series Compact (Approximately 2001–2004)

• BMW E46 316ti – N42 Engine
• BMW E46 316ti – N46 Engine
• BMW E46 318ti – N42 Engine
• BMW E46 318ti – N46 Engine

Additional BMW Applications – Complete Kit Verification Required

The following vehicles are associated with broader N42/N46 crankcase ventilation repair kits. They should not be treated as confirmed applications for every component in a kit identified only by part number 11157513903.

BMW E81/E87 1 Series

• BMW 116i – Select N45/N46 configurations
• BMW 118i – Select N46 configurations
• BMW 120i – Select N46 configurations

BMW E90 3 Series Sedan

• BMW 318i – Select N46 configurations
• BMW 320i – Select N46 configurations

BMW E91 3 Series Touring

• BMW 318i Touring – Select N46 configurations
• BMW 320i Touring – Select N46 configurations

BMW E83 X3

• BMW X3 2.0i – N46 2.0L Engine

BMW E85 Z4 Roadster

• BMW Z4 2.0i – N46 2.0L Engine

Aftermarket catalogs list complete crankcase ventilation repair kits for E90, E91, E83 X3, and E85 Z4 applications. However, these kits may include different combinations of hoses and oil separator components. Verify the complete kit's individual part numbers before advertising compatibility with these models.

Engine Compatibility

BMW N42 Engine Family

• BMW N42B18 – 1.8L Four-Cylinder Gasoline Engine
• BMW N42B20 – 2.0L Four-Cylinder Gasoline Engine

BMW N46 Engine Family

• BMW N46B18 – 1.8L Four-Cylinder Gasoline Engine
• BMW N46B20 – 2.0L Four-Cylinder Gasoline Engine

OEM Reference Part Numbers

• 11157513903 – Crankcase Breather Hose / Return Pipe
• 11617503520 – Crankcase Ventilation Oil Separator
• 11157503524 – Crankcase Ventilation Hose
• 11157503523 – Additional Crankcase Ventilation Hose
• 11157503522 – Additional Ventilation Hose Reference
• 11157533346 – Oil Return Pipe for Select Applications

Important Part Number Information

BMW part number 11157513903 identifies a specific ventilation hose rather than the entire crankcase ventilation assembly.

Aftermarket kits commonly group several of the listed reference numbers together because the individual components form part of the same ventilation system. These numbers identify different parts and should not be presented as interchangeable replacements.

The exact number of hoses, valves, and fittings included in this WAP03 kit must be confirmed against the supplier's product photographs or packing list.

Installation

• Factory-style replacement crankcase ventilation components for compatible BMW N42/N46 engines.
• Professional installation is recommended because access to the oil separator and associated ventilation hoses may require removal of surrounding intake components.
• Allow the engine to cool completely before beginning the replacement procedure.
• Locate the existing crankcase ventilation oil separator and associated breather hoses.
• Remove the necessary engine covers, intake ducting, or surrounding components required to access the ventilation assembly.
• Inspect the original hoses for cracks, hardened sections, damaged connectors, oil residue, and other signs of deterioration.
• Inspect the oil separator and surrounding ventilation connections for accumulated deposits, damaged seals, or evidence of abnormal crankcase pressure.
• Carefully disconnect the original breather hoses from their corresponding engine and oil separator connections.
• Use caution when removing aged plastic connectors, as prolonged exposure to engine heat can make these components brittle.
• Remove the original oil separator if it is included in the replacement procedure.
• Inspect the separator mounting location and surrounding connections for contamination or damaged sealing surfaces.
• Compare each replacement component with its corresponding original part before installation.
• Verify that the replacement hoses have the correct length, diameter, shape, connection orientation, and mounting configuration.
• Inspect all required O-rings, gaskets, retaining clips, and sealing components.
• Replace damaged or deteriorated seals according to the appropriate BMW service procedure.
• Install the replacement oil separator in its corresponding factory location when applicable.
• Connect the replacement crankcase ventilation hoses to their designated engine and oil separator connections.
• Ensure all hoses are fully seated without twisting, kinking, or excessive tension.
• Verify that each hose follows the original factory routing and maintains adequate clearance from moving or high-temperature components.
• Inspect the oil return connection for restrictions or accumulated deposits.
• Reinstall any intake components, mounting hardware, and engine covers removed during the replacement procedure.
• Tighten mounting hardware according to the appropriate BMW service specifications.
• Start the engine and inspect the replacement ventilation connections for abnormal noises, air leaks, or visible oil leakage.
• Verify that the engine idles normally and that the ventilation system operates without obvious leaks.
• If rough idling, excessive oil consumption, or ventilation-related fault codes persist, inspect the remaining intake and crankcase ventilation components.
• Perform an appropriate intake smoke test or crankcase pressure test when necessary to confirm proper system operation.

Replacing mechanical crankcase ventilation components does not ordinarily require engine control module programming or electronic calibration.

However, the exact replacement procedure varies depending on the engine configuration and components being replaced. Consult the appropriate BMW service documentation for vehicle-specific instructions.

Compatibility Notes

• Verify the Original BMW Part Number: Confirm that your vehicle uses crankcase breather hose 11157513903 before ordering.

• Confirm Complete Kit Contents: The product is described as an oil separator valve and breather hose kit. Verify the exact number of hoses, valves, and fittings included before publishing a complete kit contents list.

• BMW Part Number 11157513903: This reference identifies a crankcase ventilation hose/return pipe, not the oil separator valve itself.

• Oil Separator Reference: BMW part number 11617503520 identifies a separate oil separator component commonly associated with N42/N46 ventilation repair kits.

• BMW E46 Compatibility: The individual hose reference 11157513903 is documented for select E46 316i, 318i, 318Ci, 316ti, and 318ti applications equipped with N42/N46 engines.

• BMW E90/E91 Compatibility: Some aftermarket crankcase ventilation repair kits cover E90 and E91 N46 engines, but the complete kit configuration must be checked individually.

• BMW E81/E87 Compatibility: The original product title references E81 applications. Do not assume compatibility based only on the N46 engine designation; confirm the exact ventilation hose and oil separator configuration.

• BMW X3 E83 Compatibility: Select N46-powered X3 2.0i models use related crankcase ventilation components, but individual hose and oil return pipe configurations may differ.

• BMW Z4 E85 Compatibility: Select Z4 2.0i models equipped with N46 engines use related ventilation components. Verify the vehicle's production date and original part numbers.

• Left-Hand-Drive Considerations: At least one aftermarket complete kit associated with part number 11157513903 is listed specifically for left-hand-drive E46 vehicles. Verify whether the supplied WAP03 kit has the same restriction.

• Inspect the Original Hose Configuration: Compare the replacement hoses' lengths, connection diameters, routing, and fittings with the original components before installation.

• Check the Oil Separator Connections: Damaged seals or improperly seated connections can cause vacuum leaks even when the replacement oil separator is functioning correctly.

• Vacuum Leaks May Have Multiple Sources: Rough idling, unstable engine speed, and lean-running conditions can also result from damaged intake boots, intake manifold gaskets, vacuum lines, or other unmetered-air leaks.

• Oil Consumption Requires Proper Diagnosis: Excessive oil consumption can result from crankcase ventilation problems, but it may also be associated with worn piston rings, valve stem seals, external oil leaks, or other mechanical conditions.

• Inspect the Oil Return System: Restricted oil return passages can interfere with effective oil separation. Inspect the corresponding return connections when servicing the crankcase ventilation system.

• Check for Excessive Engine Blow-By: Abnormal crankcase pressure may result from ventilation restrictions or excessive combustion gases escaping past worn piston rings. Replacing the ventilation components will not correct internal mechanical wear.

• Inspect Engine Seals and Gaskets: Excessive crankcase pressure can contribute to oil leakage around deteriorated engine seals. Correcting the ventilation problem may prevent further pressure-related leakage, but already damaged seals may require separate repair.

• Check for Oil Vapor Residue: Oil residue around the intake system or ventilation connections may indicate a leaking hose, damaged seal, or malfunctioning oil separator.

• Inspect Related Ventilation Components: When replacing an oil separator or breather hose, inspect the remaining ventilation connections for similar aging-related deterioration.

• Confirm Included Seals and Hardware: Replacement kits may differ in whether O-rings, gaskets, retaining clips, or mounting hardware are included. Verify the actual product contents before ordering.

• OEM Reference vs. Genuine BMW: The supplied BMW part number identifies the original equipment component being referenced. It does not independently establish that the WAP03 replacement kit is manufactured or packaged by BMW.

• Verify Fitment Using Your VIN: For the most accurate compatibility confirmation, check each component's BMW reference number against the appropriate BMW electronic parts catalog and compare the replacement components with the originals before purchasing.

Maintaining the crankcase ventilation system is particularly important for aging BMW N42 and N46 engines, where deteriorated plastic hoses, malfunctioning oil separators, and damaged ventilation connections can contribute to vacuum leaks, rough idling, excessive oil consumption, and abnormal crankcase pressure. Replacing failing ventilation components with correctly matched parts helps restore the intended ventilation pathway, support effective oil separation, and reduce recurring pressure-related problems. Inspecting the complete ventilation system during replacement can further improve engine reliability and help preserve the smooth, dependable operation of your BMW four-cylinder engine.