Radiator Caps: Description
Radiator cap consists of pressure valve and vacuum valve. Cap has several different functions: preventing coolant loss when vehicle is in motion; preventing impurities from entering cooling system to minimize corrosion; allowing atmospheric pressure to eliminate vacuum that occurs in system during engine cooling period; and raising coolant boiling point approximately 3°F (1.6°C) per psi increase by maintaining constant cooling system pressure. See COOLANT SPECIFICATIONS.
NOTE:
Cap should maintain constant pressure in cooling system.