Expansion Tank Cap BMW X1 E81 E84 E87 E90 E91 Radiator Screw 7639020

BMW E87 E90 F10 F20 Expansion Tank Cap is an original cooling system component designed for select BMW models, ensuring stable pressure in the expansion tank. Thanks to its factory OEM design, the cap guarantees proper compatibility with the original tank and system tightness. A used part from disassembly is a sensible choice for drivers looking for a proven component at an attractive price.

Specifications and technical data

• SKU: 7639020
• Mark: BMW (Genuine OE)
• Condition: Used
• OEM Part Number: 7639020
• Substitutable numbers: 17117639020, 7639020, 17117521071, 7521071
• Category: Caps

Purpose and Function of the BMW Expansion Tank Cap

The BMW E87 E90 F10 F20 Expansion Tank Cap is responsible for maintaining the correct pressure in the cooling system and for the controlled release of excess vapor and fluid. A properly selected cap:

• stabilizes the cooling system operation under varying engine operating temperatures,
• reduces the risk of overheating by maintaining the correct operating pressure,
• ensures a tight seal of the expansion tank,
• is compatible with the factory safety features and thread geometry in the tank.

As a component from the caps category, the cap is designed to fit precisely into the original expansion tank in compatible BMW models, without the need for modifications.

Construction and Fitment for BMW Models

The BMW expansion tank cap is constructed as an OEM part, meaning its geometry, sealing type, and mounting method comply with the manufacturer's factory requirements. This ensures:

• proper seating against the tank rim,
• seal integrity under typical thermal loads,
• compatibility with the thread and seat used in original BMW expansion tanks of the E and F series.

Its original origin translates to reliable integration with the cooling system and predictable performance during long-term use.

Condition, Origin, and Benefits of a Used OEM Part

The offered cap is from a disassembled vehicle, allowing you to combine the advantages of an original BMW part with a more favorable purchase cost. A used OEM part is a good solution when:

• the current cap has lost its seal or has a damaged seal,
• there are problems maintaining pressure in the cooling system,
• you want to maintain consistency with the vehicle's factory specifications.

Choosing an original cap from disassembly helps maintain the factory operating parameters of the cooling system, without the risk of poor fitment that can occur with cheaper aftermarket alternatives of unknown origin.

Why Use an Original BMW Expansion Tank Cap?

Using the correct cap in the cooling system directly impacts the durability of the engine and its components. An original BMW cap:

• maintains the correct operating pressure, which promotes stable engine operating temperatures,
• reduces the risk of coolant leaks around the tank,
• ensures compatibility with original expansion tanks used in E87, E90, F10, F20 models,
• allows for consistency with service documentation and manufacturer procedures.

For workshops and individual users, this means hassle-free installation and predictable cooling system behavior after replacing the part.

Other BMW Caps and Knowledge about Disassembled Parts

If you are looking for other components from the BMW caps category for your model, check out the BMW caps available in our store to select the appropriate body and accessory components.

When planning body repairs or replacing external parts after a collision, it's worth learning about best practices for selecting disassembled parts. Read the article “Body and Chassis – Accident Repairs Using Disassembled Parts” to better plan your work and make informed choices about used OEM parts.