Oil Separators & Vent lines

Oil / Air Separator.
The Genuine Porsche Air-Oil Separator is the factory-specified unit responsible for separating oil mist from crankcase blow-by gases on modern Porsche flat-6 engines. As part of the PCV system, it ensures clean ventilation, stable crankcase pressure, and proper oil control - critical for protecting the intake system and maintaining optimal engine performance.

Fits:
Porsche 987.2 Boxster 2009 - 2012
Porsche 981 Boxster 2012 - 2016
Porsche 981 Boxster Spyder 2016>>
Porsche 982 Boxster GTS 4.0L 2017>>
Porsche 987C.2 Cayman 2009 - 2012
Porsche 981C Cayman 2014 2016
Porsche 981C Cayman GT4 2016>>
Porsche 982C Cayman GT4 4.0L 2017>>

Diagram ref no 16

A factory-original air-oil separator designed to filter blow-by vapours, remove oil mist, and maintain stable crankcase ventilation.

Sold individually. It is recommended to also inspect and, if necessary, replace associated hoses and seals when fitting a new separator to ensure full system integrity.

This AOS:
•  Removes oil droplets and vapour from crankcase gases before they enter the intake
•  Maintains correct crankcase vacuum and pressure balance
•  Reduces oil consumption and prevents oil contamination in the intake tract
•  Helps prevent carbon build-up, fouled sensors, and smoky exhaust
•  Ensures emissions compliance and proper engine breathing




Related reference numbers
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0PB115099A

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Oil / Air Separator.
A crankcase air-oil separator (AOS) that traps oil droplets and vapour from the engine’s blow-by gases and returns cleaned air to the intake system while keeping oil inside the engine’s lubrication system.
Sold individually. It is recommended to also inspect and, if necessary, replace associated hoses and seals when fitting a new separator to ensure full system integrity.

Fits:
Porsche 987.2 Boxster 2009 - 2012
Porsche 981 Boxster 2012 - 2016
Porsche 981 Boxster Spyder 2016>>
Porsche 982 Boxster GTS 4.0L 2017>>
Porsche 987C.2 Cayman 2009 - 2012
Porsche 981C Cayman 2014 2016
Porsche 981C Cayman GT4 2016>>
Porsche 982C Cayman GT4 4.0L 2017>>

Diagram ref no 16

This air-oil separator is an replacement unit designed to filter crankcase blow-by vapours on Porsche engines, separating oil mist from the air before routing clean air back into the intake or ventilation system.

Over time AOS units degrade - internal baffles can become clogged, seals can fail, or plastic can crack due to heat cycles. A faulty or clogged separator may allow oil vapour into the intake, causing:
•  Increased oil consumption and oil-soaked intake/tracks.
•  Blue or grey smoke from exhaust, rough idle, misfires or poor running.
•  Sludge or carbon buildup, fouled sensors, and potential engine damage.

Replacing with a correct fresh separator restores clean crankcase ventilation, keeps oil inside, and helps maintain reliable performance and engine health.

You should replace the air-oil separator when:
• You notice oil in the intake system, oil residue around intake or throttle body, or excessive oil consumption.
• The separator is showing signs of age: cracks, hardened plastic, degraded seals, or clogging.
• Your engine exhibits excessive smoke, rough idling, or misfires potentially related to intake contamination.
• Carrying out engine maintenance, PCV servicing, or installing new hoses/seals.
• The separator hasn’t been replaced for many years or high mileage - preventive maintenance helps avoid more serious issues.

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

0PB115099A

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Oil separator. One of the most common failures in the Boxster or 996 is the Air/Oil Separator, also referred to as the AOS.



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.

Fits:
Porsche Boxster 986 1997-02

Click 'Zoom in' for large parts diagram.
Diagram Ref No 1.

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

99610702304

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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 vapours

Over 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

Oil / air separator. One of the most common failures in the Boxster or 996 is the Air/Oil Separator, also referred to as the AOS.



Fits:
Porsche Boxster 986 2003>>
Porsche Boxster 987 2005>>
Porsche Cayman 987 2005>>

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.

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

99610702602

The product you are viewing cross references to these numbers

AOS Oil / Air Separator 

Maintain the performance and reliability of your Porsche Boxster 986 with this OE Match Oil / Air Separator (AOS). A critical component of the M96 engine crankcase ventilation system, the Air Oil Separator helps separate oil vapour from crankcase gases before they are returned to the engine intake system.

Fits:

• Porsche Boxster 986 2.7L 2003-04
• Porsche Boxster S 986 3.2L 2003-04
• Porsche Boxster 987 2.7L 2005-08/08
• Porsche Boxster 987 S 3.2/3.4L 2005-08/08
• Porsche Cayman 2.7L 987C 2006-08
• Porsche Cayman S 3.4L 987C 2005-08

Diagram ref no 1

During normal engine operation, pressure builds inside the crankcase and oil vapour becomes suspended within the circulating gases. The AOS removes this oil mist, allowing the oil to return to the engine while directing cleaned gases back into the intake system for emissions control and efficient combustion.

The Air Oil Separator is a well-known service item on Porsche M96 engines. As the internal diaphragm ages and deteriorates, the separator can lose its ability to regulate crankcase vacuum correctly, leading to a variety of drivability and engine performance issues.

Manufactured to OE Match specifications, this replacement unit provides the correct fitment and performance needed to restore proper crankcase ventilation and engine operation.

What Does the Oil / Air Separator Do?

The AOS forms part of the Positive Crankcase Ventilation (PCV) system and performs several important functions.

Its primary roles include:

• Separating oil from crankcase vapours
• Returning oil to the engine
• Regulating crankcase vacuum
• Reducing oil consumption
• Supporting emissions control
• Maintaining engine efficiency
• Preventing excessive oil contamination of the intake system

Without a functioning AOS, excess oil can be drawn into the intake system and combustion chambers.

Why Do Air Oil Separators Fail?

The Air Oil Separator contains an internal diaphragm and valve assembly that is constantly exposed to heat, vacuum and engine oil vapours.

Common causes of failure include:

• Diaphragm deterioration
• Age-related wear
• Heat cycling
• Oil contamination
• Internal valve failure
• High engine mileage
• Crankcase pressure fluctuations
• Long-term exposure to engine vapours

Over time, the separator loses its ability to regulate crankcase pressure correctly.

Symptoms of a Failing AOS

A failing Air Oil Separator often produces noticeable warning signs.

Common symptoms include:

• Excessive white smoke from the exhaust
• Increased oil consumption
• Rough idle
• Vacuum leaks
• Whistling or squealing noises
• Check engine warning lights
• Oil residue in the intake system
• Excessive crankcase vacuum
• Difficulty removing the oil filler cap while the engine is running

These symptoms are common indicators that the separator requires replacement.

When Should the AOS Be Replaced?

Replacement is recommended whenever symptoms of failure appear.

The AOS should also be considered during:

• High-mileage maintenance
• Engine rebuilds Intake system servicing
• Preventative maintenance programmes
• Crankcase ventilation system repairs

Many Porsche specialists regard the Air Oil Separator as a preventative maintenance item on ageing M96 engines.

Why Replacement Matters

A failing AOS can affect engine performance, emissions and long-term reliability.

Benefits of replacement include:

• Improved idle quality
• Reduced exhaust smoke
• Lower oil consumption
• Correct crankcase pressure regulation
• Improved engine efficiency
• Reduced intake contamination
• Enhanced reliability
• Restoration of factory engine operation

Replacing a failing separator early can help prevent additional maintenance costs and drivability concerns.

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

99610702602

The product you are viewing cross references to these numbers

Crankcase breather hose connector.



Fits:
Porsche Boxster 986 >>2002
Porsche 996 Carrera M >> 663 09950 Cyl 4-6

Click 'Zoom in' for large parts diagram.
Diagram ref no 6

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

99610704751

The product you are viewing cross references to these numbers

Crankcase breather hose.



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

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99610714755

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