AOS Oil / air separator. Porsche Boxster 986 1997-02  ❭  99610702304

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

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