Audi A6 C7 A8 D4 Coolant Expansion Header Tank Reservoir 4G0121403AG

Audi A6 C7 A8 D4 Coolant Expansion Header Tank Reservoir is an original cooling system component by Audi, designed for precise compatibility with the factory installation in A6 C7 and A8 D4 models. It ensures stable operation of the cooling system, allowing for proper compensation of fluid volume and maintaining safe engine thermal parameters.

Specifications and technical data

• SKU: 4G0121403AG
• Mark: Audi
• Condition: Used
• OEM Part Number: 4G0121403AG
• Substitutable numbers: 4G0121403AG, 4G0 121 403 AG, 4G0121403AC, 4G0 121 403 AC
• Part type: Coolant Expansion Tank
• Category: Expansion & Overflow Tanks

Purpose and function in the cooling system

The presented expansion tank is responsible for the controlled collection and return of coolant during changes in engine operating temperature. Thanks to a properly designed working chamber and connection ports, it works in harmony with the factory water pump, radiator, and hoses, stabilizing pressure throughout the entire system. A properly selected expansion tank in the Audi A6 C7 and A8 D4 helps reduce the risk of overheating, airlocks, and uncontrolled leaks, which translates into safer and more predictable engine performance.

Original Audi fitment

As a component from the Expansion tanks group dedicated to Audi, this part has been designed for specific mounting points and hose routing in the engine bay. This means:

• factory fitment to brackets and supports,
• compatibility of port diameters with original hoses,
• correct positioning of the cap and venting ports relative to the rest of the system. Such a solution facilitates installation and minimizes the risk of leaks resulting from imprecise fitment or the need for modifications.

Performance characteristics and benefits

The used expansion tank for the Audi A6 C7 and A8 D4 is a solution that allows for restoring the proper operation of the cooling system while maintaining the factory design concept. In practice, this means:

• maintaining the correct coolant level under various load conditions,
• pressure stabilization in the system, which promotes even engine cooling,
• compatibility with standard sensors and cooling system accessories (if present in the vehicle's configuration),
• the possibility of an economical repair while maintaining the original Audi specification. For the user, this means more predictable operating temperatures and a reduced risk of failures resulting from operating with a damaged or leaking tank.

Condition and service application

The item is offered in used condition, making it an attractive alternative for maintenance repairs, replacement after mechanical damage, or work related to cooling system upgrades. Choosing an original tank from disassembly allows for maintaining consistency with the vehicle's factory construction, which is important both from the perspective of durability and subsequent service diagnostics.

Cooling system expansion in Audi

If you are planning a comprehensive repair or upgrade of the cooling system area in your Audi and need other elements from the same group, such as additional tanks, mounting elements, or related components, check the available parts in the Audi expansion tanks category. To better understand how the selection of original, including used, components affects the driving characteristics and durability of your car, it is worth reading our expert material: Audi and emotions in their purest form. How do used parts help maintain the brand's DNA?.