--- The radiator pressure cap prevents trapping of air in the cooling system. The air in the system will cause poor cooling and cause corrosion to the cooling system components.
--- The coolant in the external reservoir will be pulled back, leaving no room for air.
--- The pressure cap is an important component of the proper working of an engine. it should be periodically inspected and consider a replacement if it fails. Ensure 5o/5o water and anti-freeze agent is used.

