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Oil Separators & Vent lines
By OE Match
- Porsche Boxster 986 2.5L 1997-99
Fits: Porsche Boxster 986 2.5L M96.20
The AOS is basically a small diaphragm distillery which distills the minute amounts of oil mist in the crankcase, liquifies it and sends it back to the crankcase. The "clean" air is now sent into the air intake (after the throttle body) to be burned off by the engine.
When the AOS starts to fail it cannot separate all of the oil out of the mist and some liquid oil is sent to the air intake.
A few drops of oil is enough to generate the GREAT SMOKE BOMB for which our cars are famous for.
A big smoke bomb once in a while is completely normal, due to the architecture of the flat-6 engine, which may let a drop of oil flow into one of the combustion chambers sporadically.
Click 'Zoom in' for large parts diagram.
Diagram Ref No 1, 4, 5, 10
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
OILSEPARATOR.986.1.OEM
The product you are viewing cross references to these numbers
This kit is comprised of the following items:
- Porsche Boxster 986 2.5L 1997-99
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
AOS Oil / Air Separator
Keep your Porsche Boxster 986 running smoothly with this OE
Match Air Oil Separator (AOS). Designed for 1997-2002 Porsche
Boxster 986 models equipped with the M96 flat-six engine, the Air Oil Separator
is a vital component of the engine's crankcase ventilation system.
Fits:
- Porsche Boxster 986 2.5L 1997-99
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
Diagram Ref No 1
During normal operation, combustion gases and oil vapours accumulate within the engine crankcase. The Air Oil Separator separates oil particles from these gases, returning the oil to the engine while directing cleaned vapours back into the intake system for combustion. This process helps maintain engine efficiency, reduce emissions and prevent excessive oil contamination within the intake tract.
The Air Oil Separator is one of the most recognised maintenance items on Porsche M96 engines. As the internal diaphragm ages, the separator can lose its ability to regulate crankcase pressure correctly, resulting in a variety of performance and drivability issues.
Manufactured to OE Match standards, this replacement unit restores proper crankcase ventilation and helps maintain the performance and reliability expected from your Porsche Boxster.
What Does the Air Oil Separator Do?
The Air Oil Separator forms part of the Positive Crankcase Ventilation (PCV) system.
Its primary functions include:
- Separating oil from crankcase gases
- Returning oil back into the engine
- Regulating crankcase vacuum
- Reducing oil consumption
- Supporting emissions control systems
- Maintaining engine efficiency
- Preventing excessive oil contamination of the intake system
A correctly functioning AOS helps the engine breathe properly while minimising oil carryover into the intake manifold.
Why Do Air Oil Separators Fail?
The internal diaphragm and valve assembly are constantly exposed to engine heat, oil vapours and vacuum pressure.
Common causes of failure include:
Diaphragm deterioration Heat cycling Age-related wear Oil contamination Internal valve failure High mileage Crankcase pressure fluctuations Long-term exposure to engine vapoursOver time, the separator loses its ability to maintain the correct crankcase vacuum levels.
Symptoms of a Failing AOS
The Porsche Boxster Air Oil Separator often provides several warning signs before complete failure.
Common symptoms include:
- Excessive white smoke from the exhaust
- Increased oil consumption
- Rough or unstable idle
- Whistling noises from the engine
- Vacuum leaks
- Check engine warning light
- Oil contamination within the intake system
- Excessive crankcase vacuum
- Difficulty removing the oil filler cap with the engine running
These symptoms typically indicate the separator is no longer functioning correctly.
When Should the AOS Be Replaced?
Replacement should be considered when any of the above symptoms are present.
The AOS is also commonly replaced during:
- High-mileage maintenance
- Engine rebuilds
- Intake system servicing
- Preventative maintenance schedules
- Crankcase ventilation system repairs
Many Porsche specialists recommend replacing the AOS before complete failure to avoid more serious drivability concerns.
Why Replacement Matters
A failed Air Oil Separator can significantly affect engine performance and reliability.
Benefits of replacement include:
- Reduced exhaust smoke
- Improved idle quality
- Lower oil consumption
- Correct crankcase pressure regulation
- Improved engine efficiency
- Reduced intake contamination
- Enhanced reliability
- Restoration of factory engine performance
Replacing the separator early helps prevent secondary issues and maintains the health of the M96 engine.
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99610702304
The product you are viewing cross references to these numbers
- Porsche Boxster 986 2.5L 1997-99
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
- Porsche 996 C2 3.4L 1997-08/01
- Porsche 996 C4 3.4L 1997-08/01
- Porsche 996 C2 3.6L 09/01-2005
- Porsche 996 C4 3.6L 09/01-2005
- Porsche 996 C4S 3.6L 09/01-2005
Fits:
Porsche Boxster 986 >>2002
Porsche 996 Carrera M >> 663 09950 Cyl 4-6
Click 'Zoom in' for large parts diagram.
Diagram Ref No 4
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99610714755
The product you are viewing cross references to these numbers
- Porsche Boxster 986 2.5L 1997-99
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
- Porsche Boxster 986 2.7L 2003-04
- Porsche Boxster S 986 3.2L 2003-04
- Porsche 996 C2 3.4L 1997-08/01
- Porsche 996 C4 3.4L 1997-08/01
Fits:
Porsche 986 Boxster - 1997 to 2004
Porsche 996 C2 / C4 3.4ltr - 1998 to 2001
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Diagram ref no 9
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99951263000
The product you are viewing cross references to these numbers
- Porsche Boxster 986 2.5L 1997-99
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
- Porsche Boxster 986 2.7L 2003-04
- Porsche Boxster S 986 3.2L 2003-04
- Porsche 996 C2 3.4L 1997-08/01
- Porsche 996 C4 3.4L 1997-08/01
Fits:
Porsche 996 1998-02 3.4L
Porsche Boxster 986
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Diagram Ref No 10.
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99610723752
The product you are viewing cross references to these numbers
- Porsche Boxster 986 2.5L 1997-99
Fits:
Porsche Boxster 986 2.5L 1999
Vehicles with chassis numbers from 65X01420
Diagram Ref No 5.
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99610714506
The product you are viewing cross references to these numbers
- Porsche Boxster 986 2.5L 1997-99
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
- Porsche Boxster 986 2.7L 2003-04
- Porsche Boxster S 986 3.2L 2003-04
- Porsche 996 C2 3.4L 1997-08/01
- Porsche 996 C4 3.4L 1997-08/01
- Porsche 996 C2 3.6L 09/01-2005
- Porsche 996 C4 3.6L 09/01-2005
- Porsche 996 C4S 3.6L 09/01-2005
- Porsche 996 TURBO 2000-05
Fits:
Porsche 986 Boxster - 1997 to 2004
Porsche 996 - 1997 to 2005
Porsche 996 turbo - 2000 to 2005
- Guaranteed fitment
- Helps prevent harmful fuel vapors from escaping into the atmosphere
- Failing Vapor Canister Purge Valve can create a vacuum leak and cause rough idle.
- Helps restore proper air to fuel ratio for optimal gas mileage.
Click 'Zoom in' for large parts diagram.
Diagram ref no 9
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99660521301
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OEMatch Oil Separators & Vent lines — Durability, Sealing, Performance
The oil separator and vent line system manages crankcase ventilation on Porsche engines by separating oil vapour from blow-by gases and returning cleaner air to the intake. Properly functioning separators and breather hoses reduce oil contamination and help preserve throttle response, idle quality and long-term engine cleanliness. OEMatch supplies replacements and related hoses prepared for Porsche applications to support routine maintenance and rebuilds.
Available Types- Oil separators (breather housings)
- Breather hoses and vent lines
- Seals, grommets and connection fittings
OE (Original Equipment) refers to parts matching original specifications for the oil separators & vent lines and may be supplied by alternative manufacturers. Aftermarket parts offer alternative options, sometimes with enhanced features or better value. OEMatch supplies non-OEM oil separators & vent lines engineered as direct-fit alternatives to OEM parts, made to original-spec dimensions and tolerances for Porsche models.
The oil separator and vent system controls crankcase pressure, removes oil vapour from circulating gases and keeps intake air free of oil droplets.
When functioning correctly the system prevents oil entering the intake tract, reduces smoke and limits carbon build-up on inlet valves and ports. OEMatch also maintains a catalogue of more than 4,000 individual part numbers and over 8,700 OE cross-references to aid correct selection for Porsche applications.
- Restores clean airflow and stable crankcase pressure
- Reduces oil leaks, blue smoke and carbon accumulation
- Supports consistent idle and throttle response
- Clogged or degraded internal membranes inside separators
- Cracked, hardened or collapsed breather hoses due to heat and age
- Worn seals, grommets or connection points causing leaks
- Vacuum leaks affecting idle and throttle response
- Sludge or condensation build-up inside vent lines
Replacing a worn or damaged separator or vent line restores correct crankcase breathing and helps avoid progressive engine issues such as oil contamination, valve deposits and inconsistent running. Fitted components specified for Porsche engines help preserve emissions performance and reduce the risk of oil reaching the intake tract. Select parts that match the original connections and materials for reliable long-term operation.
Advantages- Direct-fit replacements engineered to match original dimensions and tolerances
- Components manufactured in heat- and oil-resistant materials for longevity
- Catalogue cross-references and part numbers to support correct selection for Porsche models
Installation should be carried out by a qualified technician following model-specific procedures and torque settings. Use calibrated tools and new fasteners where specified. If you are unsure about hidden sensors or routing, seek professional installation to ensure correct sealing and operation.
