HKS Limited Edition Performance Radiator Cap – MX-5 MK1 / MK2 / MK3 / MK4 • 15009-AK004

HKS Limited Edition Performance Radiator Cap – 15009-AK004

HKS Limited Edition performance radiator pressure cap for Mazda MX-5 MK1 / NA, MK2 / NB, MK2.5 / NB-FL, MK3 / NC and compatible MK4 / ND petrol models using the S-Type radiator cap fitting and 108 kPa (1.1 kgf/cm²) pressure specification.

The HKS performance radiator cap is designed to help maintain stable cooling-system pressure during normal and demanding engine operation. Its pressure-controlled valve regulates the cooling system while allowing coolant expansion and recovery as required by the system design.

By maintaining the specified pressure within the cooling system, the cap helps raise the coolant's boiling point compared with an unpressurised system. This is particularly relevant during prolonged high-load driving, warm-weather operation and track use, where cooling-system performance is especially important.

The HKS S-Type cap features a nominal valve opening pressure of 108 kPa (1.1 kgf/cm²) and uses silicone rubber sealing material to provide dependable sealing at the radiator filler neck.

Featuring the distinctive HKS performance design, this cap combines a functional cooling-system service component with an appearance suitable for a carefully maintained or upgraded engine bay.

Product features and specifications:

• Product type: Performance radiator pressure cap
• Brand: HKS
• Manufacturer part number: 15009-AK004
• Product style: Limited Edition Performance Radiator Cap
• Radiator cap fitting: S-Type
• Opening pressure: 108 kPa
• Pressure equivalent: 1.1 kgf/cm²
• Sealing material: Silicone rubber
• Primary function: Maintaining and regulating cooling-system pressure
• Fitting position: Compatible radiator filler neck
• Vehicle applications: Selected Mazda MX-5 MK1, MK2, MK3 and MK4 models
• Quantity supplied: 1 radiator cap
• Quantity per vehicle: 1 for the specified fitting position
• Barcode: 4957266655283

Benefits of a Performance Radiator Cap:

• Maintains a controlled pressure within the engine cooling system.
• Helps increase coolant boiling resistance when the system operates at the specified pressure.
• Uses silicone rubber sealing material for dependable contact with the radiator filler neck.
• Provides a replacement for worn, damaged or incorrectly functioning compatible radiator caps.
• Suitable for compatible road and performance applications requiring the S-Type 108 kPa specification.

Common replacement reasons: A worn or faulty radiator cap can cause loss of system pressure, coolant leakage at the filler neck, premature coolant boiling or abnormal coolant recovery behaviour. Replacing a defective cap is an important part of maintaining the engine cooling system.

Fitment advice: This is the HKS S-Type cap with a nominal opening pressure of 108 kPa. The cap must match the radiator filler neck design and the cooling system's permitted operating pressure. It is not interchangeable with the HKS N-Type cap solely on the basis of pressure rating. On vehicles with aftermarket radiators, cooling-system conversions or modified filler necks, the installed radiator cap arrangement must be matched to the S-Type specification.

Important Cooling-System Advice: Increasing cooling-system pressure can increase the coolant's resistance to boiling, but it does not directly lower engine operating temperature. The radiator, hoses, expansion tank and associated cooling-system components must be suitable for the cap's opening pressure.

Other items to consider: When servicing or improving the engine cooling system, you may also want to consider purchasing fresh engine coolant, radiator hoses, hose clips, a replacement radiator, thermostat, coolant expansion components and appropriate cooling-system cleaning products.

Useful tools / consumables: Suitable coolant, clean workshop cloths, coolant test equipment and a cooling-system pressure tester for inspecting the condition of the complete system.

Difficulty guide: DIY Difficulty: Easy. Radiator cap replacement is straightforward when the cooling system is completely cold. Selecting the correct fitting and pressure rating is essential.

Why HKS? HKS is an established Japanese performance automotive engineering company producing components for road cars, tuned vehicles and motorsport applications. Its cooling-system component range includes performance radiator caps designed to maintain reliable cooling-system pressure under demanding operating conditions.

What's in the box: 1 × HKS Limited Edition S-Type Performance Radiator Cap, 108 kPa (1.1 kgf/cm²), part number 15009-AK004.

Installation / service notes: Never remove a radiator cap while the engine is hot or the cooling system is pressurised. Allow the engine and coolant to cool completely before removal. Inspect and clean the radiator filler neck and sealing surfaces. Check that the replacement cap matches the original neck configuration and required pressure specification. Fit the cap fully and securely, then inspect the cooling system for leaks during subsequent operation. Replace any damaged hoses, filler necks or other cooling-system components before returning the vehicle to normal service.