BMW 435i xDrive Coolant Reservoir Replacement at your home or office.

What is the Coolant Reservoir all about?

Cooling systems on vehicles are meant to remove heat from critical engine components. The fluid or coolant that circulates through the system carries the heat out of the engine to the radiator, where air flow dissipates the heat it contains. A natural reaction to the heat which the fluid experiences is expansion. If the fluid in the cooling system is at the full mark when the engine is cold, the volume will be greater when the fluid is hot due to expansion. Because the cooling system is closed and pressurized when hot, the excess hot coolant needs to go somewhere. It is pushed into a surge tank, or an overflow tank, where it remains until the engine cools down. When the engine cools, the contraction from the fluid still in the system creates a vacuum and the surge tank’s hose draws the coolant back into the system. If the coolant surge tank is cracked or broken, the coolant will leak onto the ground. An airlock will form in the cooling system when the surge tank hose only draws in air instead of coolant.