GMC 1976 ZEO 6083 Maintenance Manual page 332

SECTION 6K
ENGINE COOLING
Contents of this section are listed below:
The engine cooling system is the closed-pressure
type with thermostatic control of coolant circulation .
The radiator is equipped with separate coolers in the
right tank which aid in cooling engine oil and auto-
matic transmission fluid (See figure 1) .
The cooling system is sealed by a pressure type
radiator filler cap which causes the system to operate
at higher than atmospheric pressure . The higher
Figure 1-Radiator Core
GENERAL DESCRIPTION
ENGINE COOLING 6K- 1
SUBJECT PAGE NO.
General Description.. . .... . ... . .... . ... . . . .. . . ... . .... . ... . ... . ... . . ... . .... .... . ... . . ... . . .... . ... . .... . . ... . . ... . .... .... . ... . . 6K-1
Cooling System Trouble Diagnosis . . ... . . .. . . . .. . ... . ... . ... . . ... . . ... . . ... . .... . ... . . . .. . . .... .... . .... . . . . . . .... . .. . . . 6K-3
Draining, Flushing and Refilling Cooling System ... . . ... . .... . ... . . ... . . .... . ... . .... . .... . . ... . ... . .... . ... . . 6K-4
Water Pump .... . ... . .... . ... . . ... . . .... .... . ... . . ... . . .. . . . .. . ... . ... . . .. . . ... . . ... . . ... . .... . . .. . . . ... . . ... . ... . . ... . ... . . ... . . .. . . . 6K-5
Thermostat .. .... . ... . . ... . . ... . . ... . .... . ... . . . .. . . ... . .... . ... . ... . ... . . ... . ... . .... . ... . . .... . .... . ... . .... . . ... . . ... . .... .... . ... . . 6K-6
Fan/Fan Clutch . . . .... . . . . . . . .. . . .... .... . ... . . ... . . .. . . . .. . ... . . .. . . ... . . ... . .... . ... . . ... . . . ... . ... . .... . ... . . . .. . . ... . .... . ... . . 6K-7
Belt Tension .... . ... . . ... . . .... . . . . . .... . . .. . . . .. . . ... . ... . . ... . . . . . ... . . . .. . ... . .... . .. . . . . ... . .... . ... . . ... . . ... . . ... . .... . ... . ...
6K-9
IMPORTANT :
For maintenance recommendations and cooling system capacities,
refer to section 0 of this manual .
pressure raises the boiling point of the coolant and
increases the cooling effeciency of the radiator . The
9 pound pressure cap used raises the coolant boiling
point approximately 22°F . (-5.5°C.)
The pressure type radiator filler cap contains a
blow off or pressure valve and a vacuum or atmos-
pheric valve. The pressure valve is held against its
seat by a spring of predetermined strength which
protects the radiator by relieving the pressure if the
pressure should exceed that for which the radiator is
designed .
The vacuum valve is held against its seat by a
light spring which permits opening of the valve to
relieve vacuum created when the system cools off .
A pressure-vacuum valve radiator cap is used
which allows the coolant to expand through the pres-
sure valve in the center of the cap without building
unnecessary pressure . The expanding coolant flows
into the coolant reservoir (See figures 2 and 3) . The
vent valve closes due to expansion and coolant flow .
The nominal 9 pound pressure will not be reached
until the system is working at maximum capacity .
Any air or vapor in the cooling system will be
forced to the coolant reservoir under the liquid level
and leave through the vent tube at the top of the
reservoir. As the system cools, the extra coolant in