MMR Performance Billet Coolant Expansion Cap – Used & Recommended by PERON Automotive

At PERON Automotive, we don’t just sell performance parts—we use them. As a trusted reseller and active user of MMR Performance products, this 90mm billet coolant expansion cap is a perfect example of the quality and engineering we stand behind. It’s fitted to our own vehicles and consistently meets the standards our customers demand.

Engineered in the UK from a solid block of aerospace-grade 6061 aluminium, this cap is far more than a cosmetic enhancement. Designed as a direct OE replacement—not a stick-on cover—it provides both improved durability and visual impact.

This version fits BMW models equipped with the OE cap part number 17 11 7 639 021, delivering enhanced function thanks to sophisticated internal springing and bleed-off systems. The cap is finished in MMR’s signature gloss black anodising, with a pre-installed Viton O-ring for secure sealing straight out of the box.

Key Features:

Designed and engineered in the UK
Crafted from 6061 aerospace-grade aluminium
Direct OE cap replacement (not just a cover)
Advanced internal springing & bleed-off function
MMR’s signature gloss black anodised finish
Pre-installed factory-spec Viton O-ring
Fits OE part number: 17 11 7 639 021

Part of the wider MMR billet cap collection, this expansion cap is the perfect finishing touch to any engine bay—and it’s a proven choice by the PERON team.

BMW - E90 / E91 / E92 / E93 | 335i - Saloon / Touring / Coupe / Convertible

MMR BMW 90mm billet coolant cap for BMW

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