For sale is a Genuine BMW OEM Coolant Expansion Tank Cap, part number 17‑11‑7‑639‑020 (also listed as 17117639020). This factory original cap seals the coolant expansion/reservoir tank and helps maintain correct coolant system pressure. A proper cap is essential to prevent coolant leaks, overheating, and loss of coolant. 
• Part Number: 17‑11‑7‑639‑020 / 17117639020
• OEM: Genuine BMW — factory original part
• Function: Expansion tank / coolant reservoir cap
• Pressure Rating: 1.4 bar specification (standard BMW cooling system) 
• Condition: New

This cap is a direct replacement for the OEM part and ensures your cooling system maintains optimal pressure and performance.

BMW 1 Series:
• 128i (2008–2013)
• 135i / 135is (2008–2013)
• 1M (2011) 

BMW 2 Series:
• 228i / 228i xDrive (2014–2016)
• 230i / 230i xDrive (2017–2023) 

BMW 3 Series:
• 320i / 320i xDrive (2013–2018)
(plus many other chassis and years where this cap appears in OEM listings) 

Other BMW Models:
This OEM cap also appears in parts catalogs for additional BMW vehicles equipped with similar coolant reservoir systems (including various 4 Series, 5 Series, X Series, and more). Buyers should verify their exact fitment using part number or VIN lookup before ordering.

➡️ Please message with your VIN if you want fitment confirmed.