Is this BMW billet coolant cap a full replacement or a cover?

The MMX BMW billet coolant cap is a complete OE replacement machined from solid 6061 aerospace-grade aluminum — not a cover that clips over the factory cap. It includes an OE-specification internal valve, spring, and pre-installed Viton O-ring that maintain the correct coolant system pressure with a leak-free seal, exactly as the factory unit does.

How do I know which size to order — 60mm or 90mm?

Check the underside of your existing factory coolant expansion cap for the OE part number. If it reads 17117639024, order the 60mm. If it reads 17117639021, order the 90mm. Both sizes cover different BMW applications across the 2006-present range.

Will the BMW billet coolant cap maintain correct system pressure?

Yes. The MMX cap is fitted with an OE-specification valve and spring that function identically to the factory cap, maintaining the correct pressure rating for the coolant expansion tank. The pre-installed Viton O-ring provides a precise, leak-free seal rated for the temperature range of the BMW cooling system.

Will the anodized finish last in a coolant system environment?

Yes. The deep gloss black anodizing is applied directly to the aluminum surface, not painted on, giving it resistance to the heat, moisture, and coolant contact typical of an expansion tank cap. The Viton O-ring is also specifically chosen for chemical resistance in coolant environments.

Does this fit all BMW models from 2006 onwards?

The MMX billet coolant cap covers the majority of BMW models from 2006 to present across both the 60mm and 90mm sizes. To confirm fitment for your specific car, check the OE part number on the underside of your existing coolant cap and match it to the two part numbers listed in the Notes section.

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Description

MMX Billet Coolant Cap for BMW Vehicles (2006-Present, 60mm or 90mm)

BMW billet coolant cap from MMX Performance is a complete OE replacement for the factory plastic coolant expansion cap on 2006-onwards BMW models, CNC-machined from 6061 aerospace-grade aluminum using 5-axis precision manufacturing and finished in a deep gloss black anodize. Unlike aftermarket covers that simply clip over the existing cap, the MMX unit replaces the factory cap entirely, fitted with an OE-specification internal valve, spring, and pre-installed Viton O-ring for a precise, leak-free seal that maintains the correct system pressure. A knurled outer edge provides improved grip for removal and refitting during coolant service, making it a practical upgrade as well as an aesthetic one. Available in 60mm or 90mm to cover the two BMW expansion tank cap fitments across the 2006-present range; check the OE part number on the underside of your factory cap before ordering to confirm size. Designed and engineered in the UK; part of MMX’s engine bay billet cap lineup.

Features

Full OE replacement; not a cover CNC-machined from 6061 aerospace-grade aluminum
5-axis precision CNC manufacturing for high-quality finish
Deep gloss black anodized finish for corrosion resistance and lasting visual appeal
OE-specification internal valve and spring maintain correct system pressure
Pre-installed factory-spec Viton O-ring for a precise, leak-free seal
Knurled outer edge for improved grip during removal and refitting
Available in 60mm or 90mm to fit specific BMW applications
Designed and engineered in the UK

Applications

BMW: 2006-present

Notes

60mm fitment replaces OE part number 17117639024
90mm fitment replaces OE part number 17117639021
Check the underside of your factory expansion cap for the OE part number before ordering to confirm correct size
Sold as a single cap

Frequently Asked Questions

Is this BMW billet coolant cap a full replacement or a cover? The MMX BMW billet coolant cap is a complete OE replacement machined from solid 6061 aerospace-grade aluminum — not a cover that clips over the factory cap. It includes an OE-specification internal valve, spring, and pre-installed Viton O-ring that maintain the correct coolant system pressure with a leak-free seal, exactly as the factory unit does.
How do I know which size to order 60mm or 90mm? Check the underside of your existing factory coolant expansion cap for the OE part number. If it reads 17117639024, order the 60mm. If it reads 17117639021, order the 90mm. Both sizes cover different BMW applications across the 2006-present range.
Will the BMW billet coolant cap maintain correct system pressure? Yes. The MMX cap is fitted with an OE-specification valve and spring that function identically to the factory cap, maintaining the correct pressure rating for the coolant expansion tank. The pre-installed Viton O-ring provides a precise, leak-free seal rated for the temperature range of the BMW cooling system.
Will the anodized finish last in a coolant system environment? Yes. The deep gloss black anodizing is applied directly to the aluminum surface, not painted on, giving it resistance to the heat, moisture, and coolant contact typical of an expansion tank cap. The Viton O-ring is also specifically chosen for chemical resistance in coolant environments.
Does this fit all BMW models from 2006 onwards? The MMX billet coolant cap covers the majority of BMW models from 2006 to present across both the 60mm and 90mm sizes. To confirm fitment for your specific car, check the OE part number on the underside of your existing coolant cap and match it to the two part numbers listed in the Notes section.

About MMX Performance

MMX Performance is a UK-based specialist in performance parts for BMW and MINI vehicles, crafting high-quality upgrades that blend precision engineering, rigorous testing, and motorsport heritage. Driven by enthusiast culture, MMX designs its products in the UK and puts them through track validation to ensure durability, fitment accuracy, and on-road performance. Their catalog spans drivetrain components, spacers, hardware, and chassis enhancements, all tailored to elevate both the driving experience and visual appeal of BMW and MINI models.

Additional Information

The Bulletproof Automotive website contains many thousands of products purchased in multiple different currencies. All of the prices are entered manually and accurately at the time of entry. Due to the consistently fluctuating international exchange rates, at times prices may not be able to be honored at their original intended rate. We apologize for any inconvenience this may cause, unfortunately our website is unable to compensate dynamically for what can at times be volatile changes in the cost of items due to currency values fluctuating, changes in prices from suppliers, changes in shipping and import duties, and other factors. Rest assured that any order you place on line will be at zero risk to you in this area. If in the event your order cannot be fulfilled at the original intended website price we will offer you a 100% refund, no questions asked. We will continue to do our best to maintain updated prices and we will always continue to offer our price match guarantees as well to ensure our prices are always the best for you. In short, prices may change without notice. It is always advised to give us a call prior to placing your order online to confirm availability and to confirm current pricing.

Shipping Policy

Items that are in stock in the US, either at Bulletproof’s warehouse or at a supplier’s warehouse, are generally delivered within 7-10 days. Special order items from overseas take considerably longer. As a courtesy Bulletproof offers delivery estimates to our customers which take into consideration manufacturer availability and shipping schedule. These estimates represent our best guess based on previous orders from the manufacturer and do not in any way imply a guaranteed delivery window. Many manufacturers work in a “just in time” inventory system and often take 2-20+ weeks to produce an item once an order is submitted. All deliverable items are then sent to our Japanese warehouse. Bulletproof ships a minimum of one full ocean freight container every month from Japan, oftentimes more than one a month. Ocean freight takes an average of 4 weeks. Typically it breaks down to one week in Japan for paperwork and customs, two weeks by boat and one week in US customs/clearance. Due to the wide number of variables between manufacturer and shipping schedules, delivery estimates are simply just that – estimates. We attempt to estimate conservatively and we usually deliver faster than our estimates suggest. It is not Bulletproof’s policy to guarantee delivery time of any special order item, this is impossible for us to do. By ordering you acknowledge that there is no required delivery ETA and an order may not be canceled or altered due to manufacturing or shipping delays, all ETA’s are provided as a best guess only. Please review the full Terms & Conditions here.

BP Pricing Difference

We do pricing a little differently on our JDM brands and we believe in making things simple and clear. No hidden fees or surcharges. Every price you see includes the shipping cost to our office in Los Angeles, California and all the associated taxes/duties/fees for bringing the products into the US. The only shipping you ever pay is from our facility in the US to your location. Be wary of resellers that don’t include the cost of international shipping in their pricing on JDM parts. While we believe we’ll always have the lowest all-in price on JDM products, we offer a price match guarantee for all authentic parts purchased from authorized dealers as well. For many international customers, it’s much more affordable to ship from the USA than from Japan directly, as the air freight and ocean freight costs are typically much less. However, for customers looking to ship directly from Japan outside of North America, or domestically in Japan, we can provide pricing specifically for that scenario. Please do not hesitate to contact us with any pricing questions or concerns. Please email us at sales@bulletproofautomotive.com with any inquiries.

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