Coolant Recovery Systems: Operation
As coolant temperature rises and pressure in system exceeds pressure relief valve of radiator cap, excess coolant flows into overflow bottle. As engine cools and coolant contracts, a vacuum is formed in the system. The vacuum draws coolant, stored in overflow bottle, back into radiator. In a properly maintained cooling system, the only coolant losses will be through evaporation.
NOTE:
Overflow bottle captures and releases coolant according to temperature.