Pressure Cap - GMC G Service Manual

13. Coolant to the radiator.
• Remove the radiator pressure cap, start the engine
and let it run until the upper radiator hose becomes
hot (thermostat is open).
• Add coolant with the engine idling until the coolant
level reaches the bottom of the filler neck.
14. Radiator pressure cap, making sure the arrows line
up with the overflow tube.

PRESSURE CAP

A pressure-vent cap allows a build-up of 103 kPa (15
psi) in the cooling system. This pressure raises the boiling
point of the coolant to about 125 degrees C (257 degrees F)
at sea level. Do not remove the pressure cap to check the
engine coolant level; check the coolant visually at the see-
through coolant reservoir. Add coolant only to the reservoir.
CAUTION: As long as there is pressure in the
cooling system, the temperature can be consid­
erably higher than the boiling temperature of the
179
183
Figure 14 — Radiator Mounting (P Motorhome Models)
RADIATOR 6B2-13
solution in the radiator without causing the solu­
tion to boil. Removal of the pressure cap while
the engine is hot and the pressure is high will
cause the solution to boil instantaneously and
possibly with explosive force, spewing the solu­
tion over the engine, fenders and person remov­
ing the cap. If the solution contains flammable
anit-freeze such as alcohol (not recommended
for use at any time), there is also the possibility
of causing a serious fire.
The pressure-type filler cap contains a blow-off or pres­
sure valve and a vacuum or atmospheric valve (figure 17).
The pressure valve is held against its seat by a spring of
predetermined strength which protects the radiator by
relieving the pressure if an extreme case of internal pres­
sure should exceed that for which the cooling system is
designed. The vacuum valve is held against its seat by a
light spring which permits opening of the valve to relieve
vacuum created in the system when it cools off and which
otherwise might cause the radiator to collapse. A rubber
asbestos gasket is added to the diaphragm spring at the top
of the cap.
106
108
A. With I-Beam
FrontAxle;
Left Side Only
62. Insulator
63. Radiator
101. Upper Mounting
Panel
102. Lower Mounting
Panel
104. Nut
105. Washer
106. Nut
107. Insulator
108. Extension
Assembly
109. Radiator Support
Brace
121. Brake Pedal
Bracket
122. Bolt (7.4L Only)
123. Dash Panel
175. Bolt
176. Bolt
177. Bolt
178. Bolt
179. Bolt
180. Nut
181. Nut
182. Washer
183. Washer
L00734