The Hudson 8K0 121 405M Tank is a direct-fit OEM-style coolant expansion tank engineered for select Audi applications. It manages thermal expansion, maintains correct system pressure, and serves as the primary coolant fill point delivering reliable cooling circuit performance from day one.
$50.75
The 8K0 121 405M Tank by Hudson is a direct-fit OEM-style coolant expansion tank designed to restore dependable cooling system performance on select Audi applications. Specifically, this expansion tank accommodates the thermal expansion and contraction of coolant, maintains correct system pressure, and provides the primary fill point for the entire cooling circuit. Furthermore, the Hudson 8K0 121 405M Tank is engineered to OEM dimensions, so it installs directly using factory hose connections and mounting points no modifications required.
Expansion tank failures follow recognizable patterns, so acting on early warning signs helps prevent more serious engine damage. First, a recurring low-coolant warning even after refilling strongly indicates a slow leak from the tank body or seam joint. Furthermore, coolant puddles or dried residue beneath the front of the engine bay confirm active seepage. A persistent sweet coolant smell after driving is another reliable indicator. Additionally, original plastic tanks commonly become brittle or develop stress cracks due to prolonged heat cycling and pressure fluctuation. In more advanced cases, air enters the cooling circuit, and consequently the engine runs hotter than normal.
OEM Reference: 8K0 121 405M
Brand: Hudson — OE-quality cooling system replacement parts
Precision-molded to OEM dimensions for direct fitment
Correct port geometry for seamless hose and sensor integration
Engineered to restore proper system pressure and coolant volume control
Pressure-tested for verified sealing integrity
Before installation, inspect all coolant hoses and clamps and replace any that show cracking, softness, or swelling. Next, fill the tank to the MAX mark using the manufacturer-approved coolant type only — never mix coolant types, as doing so degrades inhibitor chemistry and accelerates internal corrosion. After filling, run the engine to operating temperature with the cabin heater set to full heat to purge any air from the system, then recheck the coolant level once the engine cools. Finally, clear any stored coolant-level fault codes and confirm all sensor connections are fully seated.
Always verify fitment by VIN before ordering.
Cross Reference Numbers
8K0 121 405A
8K0 121 405E
8K0 121 405G
8K0 121 405P
8K0 121 405R
| Year | Make | Model | Engine | Notes |
|---|---|---|---|---|
| 2013-2016 | Audi | A4 | ||
| 2008 | Audi | A5 | ||
| 2014-2016 | Audi | Q5 | ||
| 2008-2012 | Audi | S5 |
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