KIES MOTORSPORTS, LLC — TERMS AND CONDITIONS OF PURCHASE AND SALE

The MMX Performance BMW Billet Coolant Expansion Cap is a precision-engineered replacement designed to improve both the durability and appearance of your BMW's cooling system. Unlike decorative cap covers, this is a complete OE replacement that fully replaces the factory plastic coolant expansion cap while retaining all factory pressure regulation and sealing functionality.

Factory coolant caps are subjected to constant heat cycles and pressure fluctuations, which can cause plastic components to degrade over time. The MMX Billet Coolant Expansion Cap addresses this with a robust construction CNC-machined from a solid block of 6061 aerospace-grade aluminum, providing superior strength, heat resistance, and long-term reliability while adding a premium OEM+ appearance to the engine bay.

Each cap is manufactured using advanced 5-axis CNC machining before receiving a durable gloss black anodized finish for excellent corrosion resistance and long-lasting appearance. The precision-machined exterior also provides improved grip, making installation and removal easier during routine coolant service.

Unlike many aftermarket alternatives, the MMX Billet Coolant Expansion Cap arrives pre-assembled with OE-spec internal components, including the pressure valve, internal spring, and high-quality Viton O-ring seal. No parts need to be transferred from the original cap, allowing for a simple direct replacement while maintaining proper cooling system pressure and sealing performance.

Available in both 60mm and 90mm versions, the MMX Performance BMW Billet Coolant Expansion Cap replaces BMW OE part numbers 17117639024 (60mm) and 17117639021 (90mm). Please verify the part number on the underside of your existing coolant cap prior to ordering.

Product Details

• MMX Performance billet coolant expansion cap for BMW
• Available in 60mm and 90mm fitments
• Replaces BMW OE part numbers 17117639024 (60mm) and 17117639021 (90mm)
• Direct OE replacement with factory-style internals pre-installed
• Pre-installed pressure valve, internal spring, and Viton O-ring seal
• CNC-machined from 6061 aerospace-grade aluminum
• Advanced 5-axis machining for precise fitment
• Gloss black anodized finish for corrosion resistance and OEM+ appearance
• Precision-machined grip design for easier installation and removal
• Improves durability compared to the factory plastic coolant cap
• No transfer of OEM components required

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