Lunwag Coolant Reservoir Tank for Audi & VW 2006–2019 (1K0121407A) with Cap, OE Fit

The Lunwag 603-253 (1K0121407A) coolant reservoir tank with cap is a direct-fit replacement expansion tank engineered to restore your Audi or Volkswagen cooling system’s proper fluid containment and easy level monitoring.

When a cracked or leaking coolant reservoir leaves your engine vulnerable to overheating or coolant loss, swapping in a dependable replacement is a straightforward repair that prevents larger problems. This Lunwag unit is manufactured from heat-resistant plastic, matches OE fitment for many Audi and VW models from 2006–2019, and comes with a matching surge cap so you can replace the whole assembly in one service stop. The translucent construction and OEM-equivalent mounting points make it practical for both professional mechanics and DIY owners.

Will this reservoir fit my Audi or Volkswagen model?

Compatibility covers a wide range of Audi A3, Q3, RS3, TT and many Volkswagen platforms including Jetta, Passat, Golf, GTI, Beetle, CC, Eos and Rabbit across model years listed. Always verify compatibility by cross-referencing your vehicle’s original part number or using the fitment tool on the retailer page.

• Direct replacement for OE numbers 603-253 and 1K0121407A.
• Common fitment: Aud1 A3 (2006–2016), Q3 (2015–2018), RS3 (2017–2019), TT (2008–2019).
• VW coverage: Jetta (2005–2019), Passat (1993–2020), Golf/GTI (2006–2014), Beetle (2012–2019) and others.
• Confirm fit by VIN or part lookup before purchase to ensure exact application.

How durable and heat-resistant is the Lunwag replacement tank?

The reservoir is molded from high-quality, heat-resistant plastic designed to endure engine bay temperatures and vibration. Its construction resists common failure modes like cracking and premature deformation, giving you reliable service life when installed correctly.

• Heat-resistant polymer formulated for underhood environments.
• Translucent walls for simple visual coolant level checks.
• Reinforced mounting points to maintain secure attachment and seal integrity.
• Supplied with a compatible surge/coolant cap to complete the replacement.

What does installation involve and what’s included?

Installation is typically straightforward for anyone comfortable with basic automotive maintenance: drain or capture excess coolant, unbolt the old tank, swap hoses and sensors if applicable, and install the new unit using original mounting points. The product package includes one Lunwag reservoir and one surge cap so you don’t need to source additional parts for a standard replacement.

• Includes: 1 coolant reservoir and 1 surge cap for immediate replacement.
• Uses original OEM-style mounting locations and connection fittings.
• Recommended to replace hoses or sensors only if they show wear or damage.
• Follow vehicle-specific service manual for torque settings and coolant refill procedure.

How will this part help my engine’s cooling system perform?

As the expansion reservoir, this tank manages coolant overflow and stores reserve fluid while allowing trapped air to escape—critical roles for maintaining coolant levels and circulation. Replacing a failing tank restores proper containment and prevents external leaks that can lead to low coolant warnings or overheating events.

• Prevents coolant loss that causes low-level warnings and potential engine stress.
• Allows visual verification of coolant levels without removing the radiator cap.
• Works with the system’s pressurization via the supplied surge cap for consistent operating pressure.

Who is this for: The Lunwag 603-253 (1K0121407A) reservoir is aimed at Audi and Volkswagen owners and technicians seeking an affordable, OEM-form replacement for cracked, leaking, or aged expansion tanks. It’s appropriate for DIYers comfortable with basic cooling-system work and for shops that prefer a high-quality aftermarket alternative that fits specified 2006–2019 models. Always confirm fitment with your VIN or original part number before ordering to ensure an exact match for your vehicle.