COOLANT PRESSURE CONTROL CAP
Fig. 2 - Pressure Control Cap (Vacuum Valve Open)
Fig. 1 - Pressure Control Cap (Pressure Valve Open)
Remove the cap slowly after the
The radiator has a pressure control cap with a normally
engine has cooled.
closed valve. The cap, with a number 7 stamped on its
release of pressure from a heated
top, is designed to permit a pressure of approximately
cooling system can result in loss of
seven pounds in the system before the valve opens.
coolant and possible personal injury
This pressure raises the boiling point of the cooling
(scalding) from the hot liquid.
liquid and permits somewhat higher engine operating
temperatures without loss of any coolant from boiling.
To ensure against possible damage to the cooling
To prevent the collapse of hoses and other parts which
system from either excessive pressure or vacuum,
are not internally supported, a second valve in the cap
check both valves periodically for proper opening and
opens under vacuum when the system cools.
closing pressures. If the pressure valve does not open
between 6.25 psi (43.1 kPa) and 7.5 psi (51.7 kPa) or
the vacuum valve does not open at .625 psi (4.3 kPa)
Use extreme care when removing the
(differential pressure), replace the pressure control cap.
coolant pressure control cap.