WARNING: This page is about a different car, the 2018 Audi A6 Quattro, 2017 Audi A6 Quattro, and 2016 Audi A6 Quattro. However, it is still accessible from the selected car via links, so may be relevant.
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The coolant level must be at that MAX marking when the engine is cold.
Coolant level may be above MAX marking with engine at operating temperature.