The Hudson 8D0 121 403L Coolant Tank is a direct-fit OEM-style replacement for Audi B5/C5-platform and Volkswagen Passat B5 cooling systems. It accommodates thermal expansion, maintains proper system pressure, and includes the integrated coolant level sensor. Furthermore, it installs without modifications using factory hose connections and mounting points.
$22.00
The 8D0 121 403L Coolant Tank by Hudson is a direct-fit OEM-style replacement for Audi and Volkswagen B5/C5-platform cooling systems. Specifically, this tank serves the Audi A4 B5, A6 C5, S4, RS6, and Volkswagen Passat B5 — all models that share this expansion tank across their production runs. It manages three critical 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 cooling circuit. Additionally, it integrates the coolant level sensor, which actively triggers low-coolant warnings whenever fluid drops below the safe threshold. Because Hudson engineers this tank to OEM dimensions, it installs directly using factory hose connections and mounting points without any modifications.
B5 and C5-platform expansion tanks fail in predictable ways, so recognizing the early signs 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 confirm active seepage. A persistent sweet coolant odor after driving is another strong indicator. Moreover, the original tank commonly develops cracks or turns a brownish-orange color from heat cycling and age — both signs that replacement is overdue. In more advanced cases, air enters the cooling circuit through the compromised tank, and as a result the engine runs hotter than normal.
OEM Reference: 8D0 121 403L
Brand: Hudson — OEM-style replacement parts
Includes integrated coolant level sensor
Maintains proper cooling system pressure and accommodates thermal expansion
Direct bolt-on fitment — installs using factory hose connections and mounting points with no modifications required
Engineered for Audi B5/C5-platform and VW Passat B5 applications
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 G11 or G12 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.
Always verify fitment by VIN before ordering.
Cross Reference Numbers
8D0 121 403M
8D0 121 403A
8D0 121 403B
8D0 121 403C
8D0 121 403E
8D0 121 403F
8D0 121 403G
CRT 111 000S
| Year | Make | Model | Engine | Notes |
|---|---|---|---|---|
| 1997-2001 | Audi | A4 | 1.8L | |
| 1998-2001 | Audi | A4 | 2.8L V6 | |
| 1998-2001 | Audi | A6 | 2.8L V6 | |
| 2003-2005 | Audi | Allroad | 4.2L V8 | |
| 2003-2004 | Audi | RS6 | 4.2L V8 | |
| 2004-2005 | Volkswagen | Passat | 2.0L | |
| 1998-2005 | Volkswagen | Passat | 2.0L |
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