What causes the antifreeze to go to the over flow tank?

Antifreeze can flow into the overflow tank due to the expansion of coolant as it heats up during engine operation. When the engine reaches high temperatures, pressure increases, causing excess coolant to overflow into the reservoir. Additionally, a malfunctioning radiator cap or a cooling system leak can also lead to coolant being forced into the overflow tank. When the engine cools down, some of this coolant may be drawn back into the system.