The 4M0 121 403H Coolant Tank is a direct-fit OEM-style expansion tank engineered for Audi generation models. Furthermore, it manages thermal expansion, maintains correct system pressure, and provides the primary coolant fill point all using factory hose connections and mounting points without any modifications.
$45.00
The 4M0 121 403H Coolant Tank is a direct-fit OEM-style replacement designed to restore dependable cooling system performance on Audi vehicles. Specifically, this tank handles three critical functions within the cooling circuit — it accommodates thermal expansion and contraction of coolant, maintains correct system pressure, and serves as the primary fill point for the entire system. Because this tank is engineered to OEM dimensions, it installs directly using factory hose connections and mounting points without any modifications required. As a result, technicians and owners can complete the repair quickly and confidently.
Expansion tank failures follow predictable patterns, so recognizing the early warning signs helps prevent serious engine damage. First, a recurring low-coolant warning even after refilling strongly indicates a slow leak from the tank body or seam. Furthermore, coolant puddles or dried residue beneath the engine bay confirm active seepage. A persistent sweet coolant odor after driving is another reliable indicator. Moreover, original tanks on vehicles commonly become brittle or develop stress cracks from years of heat cycling and pressure fluctuations. In more advanced cases, air enters the cooling circuit through the compromised tank, and consequently the engine runs hotter than normal.
OEM Reference: 4M0 121 403H
Supersedes: 4M0 121 403F, 4M0 121 403D
Direct bolt-on fitment using factory hose connections and mounting points
Engineered to restore proper system pressure and coolant volume control
Before installation, confirm that all hose port positions on the new tank match those on the original unit. Next, fill the tank to the MAX mark using approved Audi G13 or G12++ coolant 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 heater set to full heat, then recheck the coolant level once the system cools completely. Moreover, inspect all coolant hoses and clamps during this service and replace any that show cracking, softness, or swelling. 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
4M0 121 403D
4M0 121 403F
| Weight | 1.60 lbs |
|---|---|
| Dimensions | 14 × 10 × 8 in |
| Year | Make | Model | Engine | Notes |
|---|---|---|---|---|
| 2017-2026 | Audi | Q7 | 3.0L V6 | |
| 2017-2026 | Audi | Q7 | 3.0 TDI |
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