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.