A recovery system maintains coolant in the system at all times.
As engine temperature rises, coolant expands. Pressure builds against a valve in the radiator cap until, at a preset pressure, the valve opens. Hot coolant flows out into an overflow container.
As the engine cools, coolant contracts and pressure in the radiator drops. Atmospheric pressure in the overflow container opens a second valve, and overflow coolant flows back into the radiator.
No coolant is lost and excess air is kept out of the system. Like water, air contains oxygen which reacts with metals to form corrosion.
