Coolant Hoses - Centre Section

Transverse Coolant Breather Line. 

The Genuine Porsche Transverse Coolant Breather Line (Part Number 99710676702) is an important engine cooling system component designed to help maintain effective coolant circulation, air removal and reliable cooling system operation on compatible Porsche models.

Fits:

• Porsche Boxster 987 2.7L 2005-08/08
• Porsche Boxster 987 S 3.2/3.4L 2005-08/08
• Porsche Boxster 987 MKII 2.9L 2009-12
• Porsche Boxster S 987 MKII 3.4L 2009-12
• Porsche 997 MK1 Carrera 2 3.6L 2005-08
• Porsche 997 MK1 Carrera 2S 3.8L 2005-08
• Porsche 997 MK1 Carrera 4 3.6L 2005-08
• Porsche 997 MK1 Carrera 4S 3.8L 2005-08
• Porsche 997 MK1 TURBO 2007-09
• Porsche 997 MK1 GT3 / GT3 RS 2007-09
• Porsche 997 MK1 GT2 2007-09
• Porsche 997 MKII Carrera C2 3.6L 2009-12
• Porsche 997 MKII Carrera C4 3.6L 2009-12
• Porsche 997 MKII Carrera C2S 3.8L 2009-12
• Porsche 997 MKII Carrera C4S 3.8L 2009-12
• Porsche 997 MKII GT3 / GT3 RS 2010-11
• Porsche 997 MKII Turbo 2010-13
• Porsche 997 MKII GT2 RS 2011-13
• Porsche Cayman 2.7L 987C 2006-08
• Porsche Cayman S 3.4L 987C 2005-08
• Porsche Cayman 2.9L 987C MKII 2009-12
• Porsche Cayman S / R 3.4L 987C MKII 2009-12  

Diagram Ref No 13

Manufactured to Porsche's original equipment specifications, this transverse breather line forms part of the vehicle's coolant ventilation circuit, providing a dedicated passage for air and coolant to move between the relevant cooling system components.

The engine cooling system relies on an effective network of coolant pipes, hoses and ventilation lines to maintain consistent operating temperatures. Air trapped within the cooling circuit can interfere with coolant circulation, reduce heat transfer efficiency and contribute to localised hot spots.

The transverse coolant breather line helps provide the intended ventilation path within the cooling system, supporting the removal of trapped air and the correct distribution of coolant throughout the circuit.

Positioned within the vehicle's cooling system pipework, the line is designed to withstand normal coolant system pressure, temperature fluctuations and vibration.

Over time, the original breather line may become damaged, cracked, corroded or weakened due to ageing, exposure to heat, repeated temperature changes or mechanical stress. A leaking or restricted breather line may contribute to coolant loss, ineffective air removal and cooling system performance problems.

Replacing a damaged or deteriorated transverse coolant breather line with a Genuine Porsche component helps restore the original ventilation arrangement, maintain cooling circuit integrity and support reliable engine temperature regulation.

Ideal for cooling system repairs, coolant leak diagnosis, radiator pipework maintenance, engine servicing and preventative maintenance.

What This Product Does:
The transverse coolant breather line forms part of the engine's cooling system ventilation circuit and performs several important functions.

• Supports Cooling System Ventilation: Provides a passage for air and coolant within the designated cooling system vent circuit.
• Helps Remove Trapped Air: Allows air to migrate through the designed ventilation path, reducing the likelihood of air pockets forming within the cooling system.
• Supports Coolant Circulation: Helps maintain the conditions required for consistent coolant movement throughout the engine cooling circuit.
• Maintains Cooling System Integrity: Provides a sealed connection between the relevant cooling system components.
• Supports Engine Temperature Regulation: Helps the cooling system operate efficiently by maintaining its intended coolant ventilation arrangement.
• Reduces Airlock Risk: Supports the removal of trapped air that could interfere with coolant circulation after servicing or coolant replacement.
• Accommodates Normal System Pressure: Designed to operate under the normal temperature and pressure conditions of the vehicle's cooling system.
• Supports Cooling System Bleeding: Provides part of the intended air removal pathway when the cooling system is filled and bled according to Porsche procedures.
• Helps Protect Engine Components: Supports reliable cooling system operation, reducing the risk of problems associated with insufficient coolant circulation.
• Maintains Original Equipment Fitment: Replaces the original transverse breather line using the specified factory routing and connections.

Symptoms Of Wear Or Failure:
Cooling system breather lines are exposed to coolant, temperature changes, vibration and environmental conditions throughout their service life.

Over time, material deterioration, physical damage or corrosion may compromise the line or its connections.

Common symptoms of a worn or failing transverse coolant breather line include:

• Coolant Leakage: Visible coolant dripping or seeping from the breather line, its fittings or connection points.
• Low Coolant Level: Repeated coolant top-ups may indicate a leak within the breather line or another part of the cooling circuit.
• Visible Cracks or Splits: Damage to the pipe or its connecting sections may allow coolant to escape.
• Corrosion or Surface Deterioration: Ageing and environmental exposure may weaken the line or its fittings.
• Damaged or Loose Connections: Worn connectors, retaining clips or seals may prevent the line from remaining securely attached.
• Dried Coolant Deposits: White, pink or coloured residue around the line may indicate previous coolant seepage.
• Coolant Warning Messages: Significant coolant loss may activate the vehicle's low coolant warning.
• Engine Overheating: Coolant loss or ineffective removal of trapped air may contribute to higher-than-normal engine temperatures.
• Air Trapped in the Cooling System: A restricted or incorrectly connected vent line may contribute to persistent air pockets.
• Unusual Cooling System Noises: Gurgling or bubbling noises may occur when air remains trapped within the coolant circuit.
• Coolant Smell: Escaping antifreeze may produce a noticeable sweet smell around the vehicle.
• Physical Damage Following Repairs: Incorrect handling, accidental impact or improper installation may damage the breather line.
• Blocked or Restricted Vent Passage: Debris or internal deterioration may obstruct the intended air and coolant ventilation path.

Why Replacement Matters:
Replacing a cracked, leaking or damaged transverse coolant breather line is important for maintaining reliable cooling system operation and protecting the engine against excessive temperature.

Key Benefits of Replacement:

• Restores Cooling System Ventilation: Helps maintain the original air removal pathway within the coolant circuit.
• Reduces the Risk of Airlocks: Supports effective removal of trapped air that can interfere with coolant circulation.
• Helps Prevent Coolant Leaks: Replaces damaged lines or connections that allow coolant to escape.
• Supports Efficient Engine Cooling: Helps maintain the conditions required for effective coolant circulation and heat transfer.
• Reduces Overheating Risk: Restoring a leaking or restricted line can help address cooling system problems that may contribute to elevated engine temperatures.
• Maintains Cooling System Pressure Integrity: Provides the specified sealed connection within the cooling circuit.
• Supports Reliable Coolant Bleeding: Helps maintain the intended ventilation route during coolant refilling and servicing.
• Protects Engine Components: Reduces the risk of overheating-related damage caused by unresolved cooling system faults.
• Genuine Porsche Quality: Manufactured to the original equipment specification for compatible vehicles.
• Correct Factory Routing: Designed to match the intended transverse breather line position and connection arrangement.
• Supports Long-Term Cooling System Reliability: Helps prevent recurring problems caused by damaged or deteriorated ventilation pipework.
• Ideal During Cooling System Repairs: Suitable for replacement when surrounding coolant pipes or hoses are being serviced.
• Supports Preventative Maintenance: Allows ageing or damaged cooling system components to be replaced before more significant failures develop.

Although the transverse coolant breather line is a relatively small part of the complete cooling system, it performs an important function in maintaining the intended ventilation arrangement.

A damaged or leaking breather line can allow coolant to escape and may interfere with the cooling system's ability to remove trapped air effectively.

Persistent coolant loss or air pockets can reduce heat transfer efficiency and contribute to overheating, potentially placing additional thermal stress on the engine.

Replacing the defective line with a Genuine Porsche component helps restore the factory cooling system configuration and support dependable engine operation.

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

99710676702

The product you are viewing cross references to these numbers

Water coolant hose, supply
OE Match coolant supply hose for selected Porsche 997.1 and 997.2 models. This replacement carries coolant along the supply circuit and provides an alternative to the original Porsche component.

Fits:
Porsche 997.1 2005 - 2008
Porsche 997.2 2009 - 2012

Diagram ref no 17

What This Product Does

The hose joins designated connections within the water-cooling supply circuit. Its role is to carry coolant between those connections, supporting circulation and temperature management. OE Match develops replacement components around Porsche applications, with specification review and sample evaluation forming part of its approval process.

Functions

• Carries coolant along the designated supply route.
• Links the relevant cooling-circuit connections.
• Supports a sealed fluid path when properly fitted.

Technical Details

• Brand: OE Match
• Component: coolant supply hose.
• Supplied part reference: 99710674006
• Additional catalogue references: 99710674004 and 99710674005.

Symptoms of Fault

• Wetness or seepage at either connection.
• A falling coolant level or dashboard level alert.
• A sweet smell or deposits near the hose.
• Temperature readings higher than usual.
• Bulging, splits, hardened areas or unusually soft sections.
• Gurgling associated with low coolant or trapped air.

Why Replacement Matters

Repeated heating and cooling, pressure, vibration and contamination can weaken a hose over time. Renew it when inspection confirms deterioration or identifies it as the leak source. A small seep can develop into substantial fluid loss, so investigate recurring level drops rather than relying on repeated top-ups.

During related cooling repairs, inspect adjoining pipes, fittings, retainers and seals. Check the hose routing and connection security, then refill and bleed according to the vehicle-specific procedure.

FAQs

How should a suspected leak be confirmed?
A cooling-system pressure test and inspection of the hose connections can help distinguish hose leakage from nearby component faults.

Can coolant collect without leaving a puddle?
Yes. Fluid may collect on an undertray or evaporate, leaving deposits rather than obvious drips.

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

99710674006

The product you are viewing cross references to these numbers

Water pipe. RETURN LINE.

Fits:
Porsche 987 Boxster MKI 2005-08
Porsche 987 Boxster MKII 2009-12
Porsche 987C Cayman MKI 2006-08
Porsche 987C Cayman MKII 2009-12

Porsche 997 Carrera 3.6L / 3.8L MKI 2005-08 COUPE / CABRIO
Porsche 997 Carrera 3.6L / 3.8L MKII 2009-12 COUPE / CABRIO / TARGA
Porsche 997 TURBO / TURBO S / GT2 / GT2 RS 2007>>
Porsche 997 GT3 2007-11

Click 'Zoom in' for large parts diagram.
Diagram ref no 2

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

99710672003

The product you are viewing cross references to these numbers

Water pipe. RETURN LINE.

Fits:
Porsche 987 Boxster MKI 2005-08
Porsche 987 Boxster MKII 2009-12
Porsche 987C Cayman MKI 2006-08
Porsche 987C Cayman MKII 2009-12

Porsche 997 Carrera 3.6L / 3.8L MKI 2005-08 COUPE / CABRIO
Porsche 997 Carrera 3.6L / 3.8L MKII 2009-12 COUPE / CABRIO / TARGA
Porsche 997 TURBO / TURBO S / GT2 / GT2 RS 2007>>
Porsche 997 GT3 2007-11

Click 'Zoom in' for large parts diagram.
Diagram ref no 2

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

99710672003

The product you are viewing cross references to these numbers