Behr Hella Service 376789761 Engine Coolant Reservoir (BMW);

Behr Hella Service combines for more then 10 years outstanding service expertise with high-quality and extensive product range. The expansion tank is used to trap the expanding coolant from the coolant circuit. High coolant temperature results in the pressure in the cooling system rising as the coolant expands. The increase in pressure is dissipated by valves integrated into the cap of the expansion tank. If the pressure increases, the system pressure is reduced by the valve and brought back to the preset value. When the coolant temperature returns to normal, a partial vacuum forms in the cooling system. This in turn results in the vacuum compensation valve in the tank's filler cap opening. Ambient air flows into the tank until the preset system pressure is reached again.