Description

BMW Coolant Expansion Tank Cap 17117521071 X3 X4 X5 X6 Z4

The Genuine BMW Radiator / Coolant Expansion Tank Cap (OEM Part # 17117521071) is a critical pressure-regulating component of the engine cooling system. Engineered to maintain system pressure up to 2.0 bar (200 kPa / 29 PSI), this expansion tank cap elevates the boiling point of the engine coolant, prevents cavitation around the water pump, and releases excessive pressure to protect sensitive cooling system components (radiator, expansion tank, and hoses) from bursting under high heat.

A failing or brittle coolant cap can cause pressure loss, leading to premature coolant boiling, overheating, low coolant warnings, dynamic vacuum collapse of coolant hoses, and chronic coolant evaporation.

Technical Specifications & Cross-References

Specification	Details
Primary BMW Part Number	`17 11 7 521 071` / `17117521071`
Superseded Part Numbers	`17 11 1 742 231` (17111742231), `17 11 7 639 022` (17117639022), `17 11 4 379 047`
Pressure Rating	2.0 Bar (200 kPa / 29 PSI) – stamped “200” on the underside
Material	Reinforced polyamide (PA66) thermal composite with dual EPDM O-ring pressure valves
Thread Type	Screw-on turn design
Package Contents	1x Expansion Tank Cap with integrated pressure relief valve assembly

Vehicle Compatibility

Compatible across multiple generations of BMW vehicles, including naturally aspirated and turbocharged 4-cylinder, inline-6, V8, and V12 engines:

BMW X Series:
- X3: E83 (2.5i, 3.0i, 3.0si), F25 (xDrive28i, xDrive35i) (2004–2017)
- X4: F26 (xDrive28i, M40i) (2015–2018)
- X5: E53 (3.0i, 4.4i, 4.8is), E70 (3.0si, 4.8i, xDrive30i, xDrive35i, xDrive50i, X5 M), F15 / F85 (2000–2018)
- X6: E71 / E72 (xDrive35i, xDrive50i, X6 M), F16 / F86 (2008–2019)
BMW Z Series:
- Z4: E85 / E86 (2.5i, 3.0i, 3.0si, Z4 M Roadster/Coupe), E89 (sDrive28i, sDrive30i, sDrive35i, sDrive35is) (2003–2016)
BMW 1, 3, 5, 6, & 7 Series:
- 1 Series: E81, E82, E87, E88 (128i, 135i, 135is) (2008–2013)
- 3 Series: E46, E90, E91, E92, E93 (323i, 325i, 328i, 330i, 335i, M3) (1999–2013)
- 5 Series: E39, E60, E61 (525i, 528i, 530i, 535i, 545i, 550i, M5) (1997–2010)
- 6 Series: E63, E64 (645Ci, 650i, M6) (2004–2010)
- 7 Series: E38, E65, E66, F01, F02 (740i, 745i, 750i, 760i) (1995–2015)

Key Features & Operational Benefits

Precision 200 kPa Pressure Control: Dual internal spring valves maintain exact baseline pressure to raise coolant boiling point past 120°C (248°F).
Dual O-Ring Hydro-Seal: High-grade synthetic EPDM seals prevent coolant micro-seepage around the expansion tank filler neck.
Over-Pressure Protection: Automatically vents excess pressure or steam if engine temperatures spike, saving plastic cooling expansion tanks from cracking.
Direct OEM Fitment: Exact thread pitch allows effortless hand tightening until seated.