X AUTOHAUX Coolant Radiator Reservoir Tank for Audi A3 8VA/8VF — 5Q0121407A Direct-Fit with Cap & 2-Pin Sensor

High-quality replacement coolant reservoir tank compatible with part numbers 5Q0121407A/D/G, supplied with cap and 2-pin sensor for select Audi, VW and SEAT models.

If your vehicle is showing low coolant warnings, coolant leaks, or the original plastic reservoir is cracked or discolored, replacing the coolant radiator reservoir tank restores proper coolant containment and sensor function. This X AUTOHAUX unit is designed as a direct-fit replacement for several VW Group models from 2012–2020, engineered to resist corrosion, deformation and fluid loss under normal operating conditions.

Which models and part numbers does this reservoir fit?

This reservoir matches OEM part numbers 5Q0121407A, 5Q0121407D and 5Q0121407G and includes the cap and a 2-pin sensor. It is intended for a range of Audi, Volkswagen and SEAT models produced roughly between 2012 and 2020.

• Compatible with Audi A3 8VA and 8VF (2012–2020).
• Fits Audi Q2 GAB (2016–2020), Audi Q3 F3 (2018–2020), Audi TT MK3 FV (2014–2020).
• Also fits Volkswagen Arteon 3H7 (2017–2020), Golf MK7 (2012–2020), Passat 3G (2014–2020) and Seat Ateca KH (2016–2020).
• Check your vehicle’s existing part number before ordering to ensure exact match.

How does this replacement reservoir help with engine cooling reliability?

The reservoir stores excess coolant and allows the cooling system to maintain proper pressure and fluid levels as the engine heats and cools. Replacing a damaged or leaking tank prevents coolant loss and helps the thermostat and radiator operate as intended, reducing the risk of overheating-related drivability issues.

• Includes a functioning 2-pin sensor so level warnings remain accurate.
• Prevents coolant leaks that can lead to low-fluid warnings or engine overheating symptoms.
• Maintains correct expansion and return of coolant during temperature cycles.

What materials and features improve long-term durability?

This X AUTOHAUX reservoir is manufactured from robust, automotive-grade plastic chosen to withstand heat, vibration and exposure to coolant additives. The design reduces the risks of cracking, deformation and corrosion compared with older, worn-out tanks.

• Durable polymer construction resists rust and oxidation.
• Engineered to limit fluid seepage and retain shape over time.
• Supplied with a cap and sensor to replace worn components in one step.

How straightforward is installation and what should I prepare?

Installation is generally straightforward for anyone comfortable working in an engine bay; basic hand tools are required and the car must be cooled and safely supported. The procedure involves draining excess coolant, removing mounting bolts and hoses, swapping the old reservoir for the new one, and reconnecting hoses and the sensor.

• Allow the engine to cool fully before starting work to avoid burns.
• Drain remaining coolant into a suitable container before disconnecting hoses.
• Reinstall clamps and bolts securely, then refill coolant and check for leaks and proper sensor operation.

Who is this for: This replacement reservoir is aimed at owners and mechanics who need an OEM-style coolant expansion tank for Audi A3, Q2, Q3, TT and compatible Volkswagen/SEAT models from the 2012–2020 era. It suits DIY enthusiasts performing scheduled maintenance or repair shops replacing worn or leaking tanks. Always confirm your vehicle’s part number and coolant specifications before purchase and follow local regulations for disposal of used coolant.