Radiator Cap

The radiator cap is designed to maintain a constant pressure in the cooling system. Most pressure caps are rated between 8 to 16 psi (55 to 110 kPa). Increasing pressure on the cooling system increases the boiling point of the coolant. The radiator cap allows expanding coolant to go to the coolant recovery tank. When the fluid has cooled, coolant is drawn back into the radiator through a vacuum valve in the cap.