X AUTOHAUX Coolant Radiator Reservoir Tank 5Q0121407A for Audi A3 2012–2020 — Direct‑Fit with Cap & 2‑Pin Sensor

X AUTOHAUX Coolant Radiator Reservoir Tank 5Q0121407A is a direct-fit replacement overflow expansion bottle with cap and 2-pin sensor designed for Audi and select VW/Seat models, restoring proper coolant containment and level monitoring.

If your vehicle shows coolant loss, a low-level warning, or you spot cracks or discoloration in the old reservoir, replacing it with a correct, high-quality tank prevents leaks and maintains engine cooling performance. This X AUTOHAUX assembly corresponds to part numbers 5Q0121407A/D/G and arrives complete with the threaded cap and the 2-pin level sensor so you can swap the unit without sourcing additional components.

Will this reservoir fit my car?

This reservoir is manufactured to match original equipment fitment for many MQB-platform vehicles. It fits Audi A3 (8VA, 8VF) 2012–2020 and many related models listed below, so verify your vehicle's part number and year before ordering.

• Compatible models include Audi A3 (8VA/8VF) 2012–2020, Audi Q2 (GAB) 2016–2020, Audi Q3 (F3) 2018–2020, Audi TT Mk3 (FV) 2014–2020.
• Also fits Volkswagen Arteon (3H7) 2017–2020, VW Golf Mk7 2012–2020, Volkswagen Passat (3G) 2014–2020, Seat Ateca (KH) 2016–2020.
• Confirm compatibility by matching your existing reservoir part number (5Q0121407A/D/G) or consulting your VIN-based parts lookup.

How does it restore cooling system reliability?

Replacing a cracked or deteriorated reservoir stops coolant leaks and restores proper expansion volume for temperature changes. The included 2-pin sensor sends accurate level information to your vehicle’s warning system, helping you avoid undetected coolant loss.

• Restores sealed coolant expansion capacity to reduce overflow and spillage.
• Replaces faulty or brittle plastic that can deform or crack with age and heat exposure.
• Reinstates the coolant level sensor for correct dashboard warnings.

What are the materials and build quality like?

The tank is made from durable, automotive-grade plastic engineered to resist rust, oxidation, and deformation under normal operating conditions. Molded mounting points and hose connections match OE dimensions to ensure a secure fit and long service life when installed properly.

• Durable construction resists fluid loss and heat-related deformation.
• OE-style mounting and hose fittings reduce installation adjustment.
• Supplied cap and sensor included to eliminate extra sourcing.

How difficult is installation and what should I prepare?

Installation is straightforward for anyone with basic mechanic skills and common tools. Work on a cold engine, catch the coolant, swap the old tank for the new unit, reconnect hoses and wiring, and top up coolant to the correct level.

• Allow engine to cool fully before starting work to avoid burns.
• Drain remaining coolant into a pan, unbolt the old reservoir, and transfer hoses carefully.
• Reinstall the new tank, tighten clamps, reconnect the 2-pin sensor, refill coolant, and test for leaks.

Who is this for: This X AUTOHAUX reservoir tank is intended for owners, DIY mechanics, and independent repair shops working on MQB-based Audis, Volkswagens, and Seats that require part numbers 5Q0121407A/D/G. It’s ideal for vehicles showing coolant level warnings, visible reservoir damage, or when performing a thorough cooling-system refresh. Always confirm fitment against your vehicle’s part number or VIN before purchase and dispose of drained coolant responsibly.