When the temperature of the cooling system of the car rises, the coolant will expand. If there is no expansion tank, the pressure of the cooling system will rise,
and the coolant will eject from the cracks or crush the parts of the cooling system, making the cooling system malfunction.
The expansion tank is used to store coolant that expands due to temperature rise. It can also be used to add coolant,
which can be added from the expansion tank if there is less coolant.