AOS Oil / air separator. Porsche Boxster 986 2003>>  ❭  99610702602

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
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99610702602

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