Coolant Circulation:
The overflow tank holds coolant.
When the coolant level in the cooling system drops too low (due to evaporation or leaks), the overflow tank releases stored coolant to replenish the system.
Temperature Regulation:
The cooling system should never change the amount of coolant within it.
Necessity of Overflow Tanks:
Older vehicles didn’t have overflow tanks; they relied on multiple vents to release excess pressure when the coolant got hot.