{"product_id":"mmx-bmw-mini-90mm-billet-coolant-expansion-cap","title":"MMX BMW \u0026 MINI 90mm Billet Coolant Expansion Tank Cap","description":"\u003cp\u003eThe \u003cstrong\u003eMMX 90mm Billet Coolant Expansion Cap\u003c\/strong\u003e is the larger of the two MMX coolant cap sizes, designed in the UK and machined from a solid billet of aluminium. It is a direct replacement for BMW and MINI models running \u003cstrong\u003eOE part number 17 11 7 639 021\u003c\/strong\u003e, and takes the place of the factory cap rather than sitting over it.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch3\u003eMatch The Cap Diameter, Not The Model\u003c\/h3\u003e\n\u003cp\u003eBMW fits both a 60mm and a 90mm expansion tank cap across its range, and the two are not interchangeable. Reading the number moulded into the existing cap is the only reliable check. This MMX cap covers OE 17 11 7 639 021; the smaller 60mm fitment is available as a separate MMX part.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch3\u003ePressure Retained, Finish Improved\u003c\/h3\u003e\n\u003cp\u003eThe expansion tank cap holds the cooling system at its designed pressure, so it has a job to do beyond appearance. Rather than a cover, MMX machines a full replacement that seals correctly while removing the discoloured plastic item that stands out in an otherwise finished engine bay.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch3\u003eKey Features\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eCNC-machined in the UK from solid billet aluminium\u003c\/li\u003e\n\u003cli\u003eDirect replacement for OE part number 17 11 7 639 021\u003c\/li\u003e\n\u003cli\u003e90mm expansion tank fitment\u003c\/li\u003e\n\u003cli\u003eNot an adhesive cover – the factory cap is replaced outright\u003c\/li\u003e\n\u003cli\u003eAnodised finish for lasting corrosion resistance\u003c\/li\u003e\n\u003cli\u003eFully reversible – the OEM cap can be refitted at any time\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr\u003e\n\u003ch3\u003eSpecifications\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e MMR03-1502\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eReplaces OE:\u003c\/strong\u003e 17 11 7 639 021\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDiameter:\u003c\/strong\u003e 90mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMaterial:\u003c\/strong\u003e Billet aluminium, anodised\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr\u003e\n\u003ch3\u003eCompatibility\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eBMW and MINI models fitted with the 90mm expansion tank cap, OE 17 11 7 639 021\u003c\/li\u003e\n\u003cli\u003eAlways confirm the part number on the existing cap before ordering\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr\u003e\n\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\n\u003cp\u003e\u003cstrong\u003eHow is 90mm confirmed against 60mm?\u003c\/strong\u003e\u003cbr\u003eRead the part number on the factory cap. 17 11 7 639 021 is the 90mm cap; 17 11 7 639 024 is the 60mm version, for which MMX offers a separate part.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan the cap be fitted with the engine hot?\u003c\/strong\u003e\u003cbr\u003eNo. A cooling system should only be opened when fully cold, exactly as with the factory cap.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch3\u003eWhy Choose An MMX Billet Cap?\u003c\/h3\u003e\n\u003cp\u003eA billet coolant cap is a small change that lifts the whole engine bay, and MMX builds it as a working pressure component rather than a decorative shell. R44 Performance stocks the complete MMX under-bonnet range.\u003c\/p\u003e","brand":"MMX","offers":[{"title":"Default Title","offer_id":57929993093502,"sku":"MMR03-1502","price":121.79,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0280\/7568\/8011\/files\/MMR03-1502_2.png?v=1787916852","url":"https:\/\/r44performance.com\/products\/mmx-bmw-mini-90mm-billet-coolant-expansion-cap","provider":"R44 Performance","version":"1.0","type":"link"}