BMW E60 E61 F10 F80 M3 F82 M4 Radiator Expansion Tank Cap 7639021

BMW E60 E61 F10 F80 M3 F82 Radiator Expansion Tank Cap is an original cooling system component from the Expansion tanks category, designed for selected BMW 5 Series and M3 models. It ensures proper sealing of the tank, stabilization of coolant pressure, and safe engine operation under a wide range of loads.

Specifications and technical data

• SKU: 7639021
• Mark: BMW (Genuine OE)
• Condition: Used
• OEM Part Number: 7639021
• Substitutable numbers: 17117639021, 7639021, 17137516004, 7516004
• Category: Expansion & Overflow Tanks

Purpose and technical function

The presented cap is dedicated to the cooling system in BMW E60, E61, F10, F80 M3, and F82 models, where it is responsible for the airtight sealing of the radiator expansion tank. A correctly selected cap maintains the appropriate operating pressure in the system, which supports efficient heat dissipation from the engine and reduces the risk of overheating.

Thanks to its OEM factory design, the cap works with the original thread and tank socket, which minimizes the risk of leaks, coolant loss, and uncontrolled pressure drops. This is particularly important in high-performance units, such as M3 versions, where the cooling system operates under greater thermal load.

Benefits of using an original BMW cap

Using an original expansion tank cap in a BMW provides a number of practical operational benefits:

• secure, airtight sealing of the expansion tank,
• maintenance of stable pressure in the cooling system,
• reduced risk of engine overheating during dynamic driving,
• proper compatibility with the factory tank and hoses,
• easy identification and matching thanks to manufacturer markings.

For BMW 5 Series and M3 users, it is especially important that cooling system components comply with factory specifications. The original expansion tank cap helps maintain predictable engine operating parameters and reduces the risk of failures resulting from incorrect coolant pressure.

Condition, fitment, and installation

The offered item is in used condition, which allows for an economical replacement while maintaining the manufacturer's original specifications. This is a good solution in situations where the current cap shows signs of wear, issues with sealing, or leaks, and you want to maintain a component consistent with the original BMW design.

Thanks to its OEM construction, the cap is ready for installation in place of the factory element, without the need for modifications or adaptations. In practice, this comes down to a simple removal of the old cap and screwing on the new one, while observing basic safety rules (installation only on a cold system, with no pressure in the tank).

Part selection by numbers and compatibility

The product has an assigned OEM part number and corresponding interchangeable numbers, which facilitates precise verification of compatibility with a specific engine version and model year of BMW. Combined with the Brand: BMW designation, this helps avoid the accidental selection of a replacement with different pressure characteristics or a different thread type.

Before purchasing, it is worth comparing the markings with the currently installed component or vehicle documentation to ensure that the cap will be fully compatible with the given expansion tank and the entire cooling system.

If you are planning a comprehensive repair or upgrade of the cooling system area in your BMW and need other components from the same group, such as additional caps, tanks, or venting elements, check out the available parts in the BMW Expansion tanks category.

Technical support and knowledge about used parts

When selecting used powertrain, cooling, or engine accessory components, it is worth following proven procedures for assessing technical condition. Practical tips on analyzing wear, avoiding common purchasing mistakes, and making informed component choices can be found in our guide: Second-hand differential – what you need to know about used differentials, sensors, and drive systems.

Summary

BMW E60 E61 F10 F80 M3 F82 Radiator Expansion Tank Cap is a practical choice for users who want to restore the proper operation of the cooling system while maintaining original BMW specifications. The used OEM component ensures proper system pressure, improves engine thermal safety, and allows for an economical yet technically correct repair.