BMW Expansion Tank Cap 17 11 7 639 020 For BMW 128i 135i 2008-2013 3.0L 228i 2014-2016 230i 2017-2021 2.0L 5Series, 4 Series 7 Series

BMW Expansion Tank Cap 17 11 7 639 020

✅ What is this part — Description

• This is a coolant/expansion-tank cap (reservoir cap / radiator cap) for the coolant expansion tank of BMW engines.
• It is rated for 1.4 bar system pressure
• It is a direct / OEM-spec replacement, intended to seal the expansion tank and maintain coolant pressure/venting.

🚗 Fitment — Which BMWs / Engines it Fits

• BMW 1 Series (128i, 135i, 1M) 2008–2013 (or 2011 for some 1M) with 3.0 L engines.
• BMW 2 Series (e.g. 228i), 2014–2016, and 230i (2017–2021) with 2.0 L engines.
• BMW 3 Series (gasoline & diesel 2.0L / 3.0L), 5 Series, 4 Series, 7 Series, SUVs like X1, X3, X5, X6, etc — essentially many BMWs using the standard expansion tank/reservoir setup in 2006–2025 timeframe.

🔄 Alternative / Related Part Numbers & Interchanges

• Official part number: 17-11-7-639-020 (same as 17117639020) — widely used OEM reference.
• This cap is said to replace an older part number: 17-11-7-521-071 in certain applications.
• Thus, if you have 17-11-7-521-071 (or earlier reservoir cap), this 639-020 cap is its official substitute.

✅ What to Check Before Buying / Installing

• Confirm your car’s coolant expansion tank type (BMW used “large expansion tank” on some models) — the cap must match the tank rim / threads.
• Ensure the pressure rating (1.4 bar) is correct for your cooling system — using wrong cap pressure may cause improper coolant boiling or overflow.
• If your BMW previously used 17-11-7-521-071, switching to 17-11-7-639-020 is acceptable (official interchange).