2012-2015 BMW 6 Series 4.4 Coolant Overflow Tank

Also known as

Coolant Expansion Tank

Coolant Reservoir

Antifreeze Tank

Radiator Overflow Bottle

Surge Tank

Coolant Catch Can

What this part does

The coolant overflow tank stores excess antifreeze as the fluid heats up and expands, safely containing it until the engine cools down and draws it back into the radiator. It sits in the engine bay and is directly integrated into the pressurized cooling system of the vehicle, housing the coolant level sensor. When the plastic degrades from constant thermal cycling, this reservoir frequently develops hairline cracks along the factory seams. A failing tank leads to sudden pressure loss, low coolant warnings, visible steam from under the hood, and potential engine overheating.

Fits these vehicles

Before you order

Because the BMW N63 4.4L V8 engine generates an extreme amount of under-hood heat, cooling system plastics become highly brittle over time. When replacing this tank, closely inspect the brittle plastic bleeder lines that connect to it, as they often snap during removal and may need to be replaced concurrently. It is highly recommended to install a new pressure cap when fitting this reservoir, as the old cap's internal spring may have weakened.