Audi RS6 C7 Expansion Overflow Coolant Reservoir Bottle Tank 4G0121403C

Audi RS6 C7 Expansion Overflow Coolant Reservoir Bottle Tank is an original cooling system component, specifically designed for the demanding RS-version powertrain. Thanks to its factory-spec construction, it ensures stable pressure in the cooling system, proper fluid circulation, and safe engine operation across a wide range of loads. It is a practical solution for users looking for a part that complies with Audi's factory specifications.

Specifications and technical data

• SKU: 4G0121403C
• Mark: Audi
• Condition: Used
• OEM Part Number: 4G0121403C
• Substitutable numbers: 4G0121403C, 4G0 121 403 C
• Category: Expansion & Overflow Tanks

Purpose and function in the cooling system

The presented reservoir belongs to the Expansion tanks category and plays a key role in compensating for coolant volume during temperature changes. It is responsible for:

• maintaining the correct fluid level throughout the entire cooling system,
• stabilizing operating pressure under high engine loads,
• safely discharging excess fluid and air,
• allowing for visual inspection of the coolant level.

By being tailored to the specific operating conditions of the RS6 C7 version, the reservoir supports efficient heat exchange and reduces the risk of engine overheating during dynamic driving.

Original origin and fitment for Audi

The component was designed by Audi as part of a cooling system with parameters consistent with the factory requirements of the RS6 C7 model. This means:

• secure fitment to factory mounts and hoses,
• preservation of the original fluid flow geometry,
• compatibility with standard cooling system fittings and accessories.

This solution facilitates installation and allows for maintaining the integrity of the entire cooling system without the need for installation modifications.

Part condition and service application

The product is offered as a used part, making it a reasonable alternative for cooling system maintenance, especially when the priority is to maintain the original design at an optimal cost. The reservoir is suitable for situations such as:

• replacing a damaged or leaking reservoir,
• repairs following engine overheating,
• comprehensive cooling system service after a collision or mechanical intervention.

Using an original expansion reservoir helps maintain stable engine operating conditions and reduces the risk of secondary failures resulting from improper pressure or fluid levels.

Benefits of using an original expansion reservoir

Choosing this component provides a range of practical operational benefits:

• Factory construction – compliance with the Audi RS6 C7 design, with no compromises in terms of fitment.
• Optimal cooling system performance – proper fluid volume compensation and pressure stabilization.
• Support for engine durability – reduced risk of overheating during intensive driving.
• Service application – the possibility of economical repair without sacrificing the original part.

Expanding your Audi cooling system service

If you are planning a comprehensive repair or upgrade of your Audi's engine bay and need other components from the same group, such as additional reservoirs, mounting hardware, or compatible housings, check out the available parts in the Audi Expansion tanks category.

For extensive service work, it is also worth taking care of other vehicle systems – including the powertrain fuel supply. If you want to deepen your knowledge regarding diagnostics, selection by OEM numbers, and maintenance of fuel supply components, check out the article Fuel system – injectors, pumps, and fuel tank: maintenance and regeneration, which discusses key service issues in a practical way.