5Q0 121 407T – Coolant Expansion Tank (URO)

Description

The 5Q0 121 407T Coolant Tank by URO is a direct-fit OEM-style replacement for MQB-platform Volkswagen and Audi cooling systems. Specifically, this tank supersedes the earlier 5Q0 121 407M and serves as the correct updated reference for affected models. It manages three essential functions within the cooling circuit — it accommodates thermal expansion and contraction of coolant, maintains proper system pressure, and provides the primary fill point for the entire circuit. Additionally, it integrates the coolant level sensor, which actively triggers low-coolant warnings whenever fluid drops below the safe threshold. Because URO engineers this part to OEM dimensions, it installs directly using factory hose connections and mounting points without any modifications.

Why Choose the URO 5Q0 121 407T Coolant Tank

URO Parts is a well-established aftermarket supplier that specializes in European vehicle components. Consequently, their parts consistently meet OEM dimensional and functional specifications. Furthermore, URO produces the 5Q0 121 407T from durable, heat-resistant materials that resist the cracking and discoloration common in aging original tanks. As a result, this replacement delivers reliable cooling system performance at a competitive price point compared to the dealer alternative.

Signs Your 5Q0 121 407T Coolant Tank Needs Replacing

Expansion tank failures follow a predictable progression, so catching them early protects the engine from serious damage. First, a recurring low-coolant warning — even after refilling — signals a slow leak from the tank body or seam. Furthermore, coolant puddles or dried pink residue beneath the front of the engine bay confirm active seepage. A persistent sweet coolant odor after driving is another strong indicator. Moreover, visible cracks or discoloration on the tank body confirm that replacement is overdue. In more advanced cases, air enters the cooling circuit through the compromised tank, and consequently the engine runs hotter than normal.

5Q0 121 407T Coolant Tank — Key Features

• OEM Reference: 5Q0 121 407T (supersedes 5Q0 121 407M)

• Brand: URO Parts — OEM-style European vehicle components

• Includes cap and integrated coolant level sensor

• Maintains proper cooling system pressure and accommodates thermal expansion

• Heat-resistant construction resists cracking and discoloration over time

• Direct bolt-on fitment — installs using factory hose connections and mounting points with no modifications required

Coolant Tank Service Notes

Before installation, confirm the new tank matches all hose port positions and sensor locations on the original unit. Next, fill the tank to the MAX mark using approved VW/Audi G12++, G13, or G13+ coolant only — never mix coolant types, as doing so degrades inhibitor chemistry and accelerates corrosion. After filling, run the engine to operating temperature and then recheck the level once it cools completely. Moreover, inspect all coolant hoses and clamps during this service and replace any that show cracking or softness. Finally, pressure-test the cooling system after installation to confirm a fully leak-free repair before returning the vehicle to service.

5Q0 121 407T Coolant Tank — Compatibility & Applications

Always verify fitment by VIN before ordering.

Cross Reference Numbers

• 5Q0 121 407M

• 5Q0 121 407AA

• 5Q0 121 407A

• 5Q0 121 407D

• 5Q0 121 407F

• 5Q0 121 407G

• 5Q0 121 407S

• 5QM 121 407B