BMW G20 G21 Radiator Coolant Expansion Overflow Tank Reservoir Bottle 8610652

BMW G20/G21 Coolant Expansion Tank is an original cooling system component designed for the 3 Series models. As part of the Expansion Tanks group, it ensures stable engine operating conditions, proper fluid volume compensation, and safe discharge of excess coolant. A used OEM BMW component is a sensible choice for professional repair or replacement of cooling system parts.

Specifications and technical data

• SKU: 8610652
• Mark: BMW (Genuine OE)
• Condition: Used
• OEM Part Number: 8610652
• Substitutable numbers: 8610652, 17138610652
• Category: Expansion & Overflow Tanks

Purpose and Function in the Cooling System

The BMW G20 G21 Radiator Coolant Expansion Overflow Tank Reservoir Bottle plays a crucial role in stabilizing the pressure and volume of coolant in modern BMW powertrains. The tank works in conjunction with the radiator, hoses, and other system components, enabling:

• compensation for fluid thermal expansion during engine heating and cooling,
• monitoring of coolant level in the circuit,
• safe discharge of excess fluid in situations of pressure increase,
• maintenance of stable cooling system operating conditions under varying engine load.

Thanks to its factory geometry and connections, the tank integrates with original hoses and mounting points, facilitating installation and reducing the risk of leaks.

Original Origin and Installation Compatibility

The presented expansion tank comes from the BMW offering, which means adherence to factory design standards, material quality, and engine bay fitment. The original part ensures:

• correct positioning of connection spigots relative to the radiator and hoses,
• compatibility with factory brackets and mounting points in the G20/G21 body,
• appropriate working capacity tailored to the cooling system's characteristics.

A used OEM component is particularly beneficial for vehicle servicing where maintaining the original cooling system architecture and compatibility with other components is important.

Condition, Verification, and Technical Aspects

The tank is offered as a used part, allowing for economical repair while maintaining original manufacturer specifications. Before installation, a standard visual inspection is recommended for leaks, the condition of spigots and connection sockets, as well as verification of correct selection for the specific engine variant of the BMW 3 Series G20/G21.

The component has a dedicated OEM part number and associated replacement numbers, which facilitates unambiguous identification in service catalogs and parts selection systems. This allows for precise confirmation of compatibility with the specific vehicle configuration before purchase and installation.

Application in Service Practice

Replacement of the expansion tank is recommended, among other things, when micro-cracks, leaks, problems with pressure maintenance, or visible mechanical damage are detected. Using an original BMW tank minimizes the risk of operational issues such as:

• drops in coolant level without visible leaks,
• engine overheating under heavy load,
• improper operation of the cooling system bleeding.

For workshops and individual users, this means stable, predictable cooling system operation and easier diagnostics in case of potential malfunctions.

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

To broaden your knowledge about the cooperation of the cooling system with other vehicle components and its impact on vehicle handling, you can refer to the advice contained in the article Steering System and Power Steering – How it Works and What Fails?, which helps to better understand the dependencies between key car systems.