Coolant Hoses - Radiator Section

Coolant Bottom Hose Supply - Left 
Keep your Porsche's cooling system operating at peak efficiency with this OE Match Coolant Bottom Hose Supply Left, designed for selected Porsche 987 Boxster, 987C Cayman and 997 models. Manufactured to OE specifications, this premium replacement coolant hose provides the correct fit, flexibility and durability required to ensure reliable coolant circulation throughout the engine cooling system.

Fits:
Porsche 987.1 Boxster / S  2005 - 2008
Porsche 987.2 Boxster / S 2009 - 2012
Porsche 987C.1 Cayman / S 2006 - 2008
Porsche 987C.2  Cayman / S 2009 - 2012
Porsche 997 GT3 2007-2010
Porsche 997.1 Carrera 2 / 2S 2005 - 2008 CABRIO/COUPE
Porsche 997.2 Carrera 2 / 2S 2009 - 2010 CABRIO/COUPE

Diagram ref no 9

This product supersedes Porsche's old part numbers: 99710662103

As a vital part of the cooling circuit, the lower supply hose carries coolant between major cooling components, helping regulate engine temperature and maintain optimum operating performance. Replacing worn or ageing coolant hoses is an important part of preventative maintenance and helps reduce the risk of coolant loss, overheating and expensive engine damage.

What Does the Coolant Bottom Supply Hose Do?
The left-hand coolant bottom supply hose forms part of the engine's coolant circulation system, allowing coolant to flow efficiently between the radiator and engine cooling circuit.

Its primary functions include:

• Carrying coolant through the engine cooling system.
• Maintaining consistent coolant circulation.
• Helping regulate engine operating temperature.
• Supporting efficient heat transfer from the engine to the radiators.
• Maintaining correct cooling system pressure.
• Helping prevent engine overheating.

A correctly functioning coolant hose is essential for reliable cooling performance in all driving conditions.

Why Do Coolant Hoses Fail?
Coolant hoses operate under constant heat, pressure and vibration. Over time they naturally deteriorate due to:

• Continuous heat cycling.
• Age-related hardening and cracking.
• Internal coolant pressure.
• Exposure to coolant additives and contaminants.
• Engine vibration.
• External abrasion from surrounding components.

As the hose ages it may become brittle, swell, soften or develop small leaks that gradually worsen over time.

When Should the Coolant Bottom Hose Be Replaced?
The coolant hose should be inspected during routine servicing and replaced whenever signs of deterioration are found, including:

• Coolant leaks.
• Cracked or perished rubber.
• Bulging sections.
• Soft or weakened hose walls.
• Coolant staining around hose joints.
• Damaged or corroded hose connections.

Many Porsche specialists recommend replacing ageing coolant hoses whenever the cooling system is being overhauled or when replacing the water pump, thermostat, radiators or expansion tank.

Right Hand Radiator Feed Pipe
This right-hand radiator feed pipe is designed for Porsche 997 and 987 Boxster / Cayman models. It forms a vital part of the front-mounted cooling system, carrying coolant from the engine towards the radiator to ensure efficient heat dissipation.

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 GT3 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 GT3 2010-11
• 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 10

With Porsche’s mid- and rear-engine layouts, coolant must travel long distances between the engine and front radiators. This makes the condition of coolant pipes critical to maintaining stable engine temperatures and preventing overheating.

What This Radiator Feed Pipe Does

The radiator feed pipe transports coolant from the engine to the front radiator on the right-hand side of the vehicle.

It helps:

• Maintain continuous coolant flow through the cooling system
• Transfer heat away from the engine to the radiator
• Support stable engine operating temperatures
• Ensure efficient cooling under all driving conditions
• Maintain proper pressure within the cooling circuit

Without a properly functioning feed pipe, coolant flow can be restricted or lost entirely.

Why Radiator Feed Pipes Fail

Over time, coolant pipes are exposed to heat, pressure and environmental conditions that lead to wear and failure.

Common causes include:

Corrosion (on metal sections)
Exposure to moisture and road debris can lead to corrosion over time.

Cracking or splitting
Plastic or rubber sections can become brittle and fail.

Seal and joint deterioration
Connections can weaken, leading to leaks.

Age-related wear
Long-term exposure to heat cycles reduces material strength.

Symptoms of a Failing Radiator Feed Pipe

• Coolant leaks under the vehicle
• Low coolant warning messages
• Engine running hotter than normal
• Visible corrosion or damage on the pipe
• Sweet coolant smell after driving

Replacing a worn or leaking pipe is essential to prevent overheating and engine damage.

Why You May Need to Replace This Pipe

Prevent Engine Overheating
A properly functioning feed pipe ensures reliable coolant circulation.

Fix Coolant Leaks
Replacing damaged pipes restores system pressure and eliminates leaks.

Maintain Cooling System Efficiency
Ensures optimal heat transfer and engine performance.

Essential Preventative Maintenance
Cooling system components should be inspected and replaced as they age.

Direct Fit Replacement
Designed to match original Porsche specifications for correct fitment.

Coolant Bottom Hose Supply, LEFT
This Genuine Porsche hose connects the engine coolant supply line to the left-side radiator. Part number 99710662105 is intended for the specific Boxster, Cayman and 997 applications listed below.

Fits:
Porsche 987.1 Boxster / S  2005 - 2008
Porsche 987.2 Boxster / S 2009 - 2012
Porsche 987C.1 Cayman / S 2006 - 2008
Porsche 987C.2  Cayman / S 2009 - 2012
Porsche 997 GT3 2007-2010
Porsche 997.1 Carrera 2 / 2S 2005 - 2008 CABRIO/COUPE
Porsche 997.2 Carrera 2 / 2S 2009 - 2010 CABRIO/COUPE

Diagram ref no 9

This product supersedes Porsche's old part numbers: 99710662103

What Is This Part?
This is the left-hand supply hose in the radiator section of the cooling system. It joins the engine coolant supply pipework to the left-side radiator, forming part of the connection between the engine cooling circuit and the front radiator assembly. The hose and its end connections must remain sound to contain coolant during operation. When investigating a leak in this area, inspect both the hose itself and the adjoining radiator and pipe connections before deciding which component needs replacement.

What Does This Part Do?

• Carries coolant: Provides the supply connection from the engine coolant line to the left-side radiator.
• Connects the cooling pipework: Joins the supply line and radiator within the radiator-section assembly.
• Contains coolant: Works with its connections to keep coolant within this section of the circuit.
• Provides a flexible connection: Accommodates small movements between the connected components.

Why Replace This Part?

Replacement may be needed if the hose develops a leak, splits, becomes swollen or shows damage around its connections. Ageing, repeated heating and cooling, or rubbing against nearby components can affect a coolant hose's condition. A damaged hose or poorly seated connection can allow coolant loss, so the source of any dampness or residue should be confirmed rather than assuming the radiator itself has failed.

During radiator or cooling-pipe repairs, inspect the existing hose and its mating connections. Renew a damaged hose and address any associated connection or support problem so that the replacement is correctly seated and does not rub against surrounding parts. Removal for another repair does not, by itself, mean an otherwise serviceable hose must be replaced.

When to Replace This Part?

• Confirmed leakage: Fresh coolant appears on the hose or at an end connection.
• Visible deterioration: The hose has cracks, splits, bulges or unusually soft sections.
• Rubbing damage: The outer surface shows abrasion or contact marks from nearby components.
• Connection damage: An end connection is damaged or cannot be seated securely.
• Repeated coolant loss: A pressure test or inspection identifies this hose or its joint as the source.
• During related repairs: Inspection after removal reveals deterioration that would make refitting inappropriate.

A low coolant warning, coolant smell or rising temperature warrants inspection of the cooling system, these symptoms do not identify this hose alone. Allow the system to cool before checking coolant levels or disturbing any connection.

Where Is This Part Fitted?

Location: In the front radiator section of the cooling system, between the engine coolant supply line and the left-side radiator. LEFT identifies the vehicle side, not the driver's seating position.

FAQs

• Could a leak here come from the radiator rather than the hose?
  Yes. Inspect the hose ends, adjoining connections and radiator for fresh wetness or dried coolant residue. A cooling-system pressure test can help establish the source.
• Should the connections be checked when replacing the hose?
  Yes. Inspect the mating connections and retaining hardware, and replace damaged items as required. The hose must be properly seated before the cooling system is refilled and checked.
• Does this replace part number 99710662103?
  Yes. This product supersedes Porsche part number 99710662103. Confirm the application against your vehicle before ordering.

Coolant Top Hose Left - Return

Maintain the efficiency and reliability of your Porsche's cooling system with this OE Match Coolant Top Hose Return Left, designed for selected Porsche 987 Boxster, 987C Cayman and Porsche 997 models. Manufactured to OE specifications, this premium replacement hose ensures dependable coolant return flow, helping your engine maintain its correct operating temperature under all driving conditions.

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 GT3 / GT3 RS 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 GT3 / GT3 RS 2010-11
• 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

The upper coolant return hose is a vital part of the cooling circuit, carrying coolant back through the system after it has absorbed heat from the engine. Replacing worn or ageing coolant hoses helps prevent coolant leaks, overheating and expensive engine repairs while maintaining the performance and reliability expected from your Porsche.

What Does the Coolant Top Return Hose Do?

The left-hand coolant top return hose forms an important part of the engine cooling circuit by returning coolant between key cooling components after it has circulated through the engine.

Its primary functions include:

• Returning coolant through the cooling system.
• Maintaining continuous coolant circulation.
• Supporting efficient engine temperature regulation.
• Helping dissipate engine heat through the radiators.
• Maintaining correct cooling system pressure.
• Ensuring reliable engine performance during all driving conditions.

A healthy coolant return hose is essential for the correct operation of the entire cooling system.

Why Do Coolant Return Hoses Fail?

Coolant hoses are subjected to constant pressure, heat and vibration throughout their service life. Common causes of failure include:

• Heat cycling causing the rubber to harden.
• Age-related cracking and perishing.
• Internal pressure weakening the hose structure.
• Chemical degradation from coolant additives.
• Abrasion against surrounding engine components.
• Swelling or softening of the hose material over time.

As deterioration progresses, the hose can develop leaks or split completely, resulting in coolant loss and the risk of engine overheating.

When Should the Coolant Top Return Hose Be Replaced?

The coolant return hose should be inspected during every routine service and replaced whenever signs of deterioration are found, including:

• Visible coolant leaks.
• Cracked or hardened rubber.
• Bulging or soft sections.
• Coolant staining around hose joints.
• Damaged hose clips or connectors.
• Perished hose material.

Many Porsche specialists recommend replacing ageing coolant hoses whenever the cooling system is being overhauled or when fitting a new water pump, thermostat, radiators or expansion tank.

• Coolant Return: Carries coolant through the left-hand radiator return circuit.
• Temperature Regulation: Supports efficient engine cooling and stable operating temperatures.
• Leak Prevention: Maintains a secure, sealed coolant connection.
• Heat Resistance: Designed to withstand coolant temperatures and operating pressures.
• Original Fitment: Maintains Porsche factory cooling system specifications.

• Coolant Leaks: Visible coolant escaping from the hose or its connections.
• Cracked Rubber: Splits, hardening or deterioration of the hose material.
• Swollen Hose: Bulging or deformation caused by ageing or pressure.
• Engine Overheating: Rising temperatures associated with coolant loss.
• Cooling System Repairs: During radiator replacement or coolant system maintenance.

• Carries coolant through the return side of the cooling system
• Forms part of the engine coolant circulation circuit
• Helps maintain correct coolant flow
• Supports stable engine operating temperatures
• Replaces aged, cracked or leaking coolant hoses
• Suitable for cooling system repair or refurbishment
• Supplied as an OE Match replacement part

• Coolant leakage
• Loss of system pressure
• Reduced coolant circulation
• Low coolant levels
• Engine overheating
• Coolant residue around hose connections

• Hose is leaking coolant
• Rubber is cracked or hardened
• Hose is swollen or deteriorated
• Coolant seepage is visible around connections
• Cooling system is being overhauled
• Associated coolant hoses are being renewed