|
The top tank is part of the pressurized system, like an extension of the radiator. When the coolant gets hot and expands beyond the pressure of the cap it will push a small amount of coolant into the bottom tank and then when it cools and contracts it will pull fluid back out of the bottom tank to replace it. This keeps the coolant from being lost and keeps the system full. Way back when the coolant was just pushed out onto the ground and you had to check the level more often.
|