Chevrolet Light Duty Truck 1973 Service Manual page 412

6 K - 2 E N G IN E C O O L IN G
The engine cooling system is designed to maintain the
tfngine at its most efficient operating temperature at all
engine speeds and all driving conditions. During
combustion of the air-fuel mixture, combustion gas
temperatures may be as high as 4500 degrees. The
cylinder walls, cylinder heads and pistons absorb some
but not all of the heat. They, in turn, must be provided
with some means of cooling to prevent permanent
damage. Temperatures higher than the limit imposed by
the oil properties will destroy the lubricating characteris­
tics of the oil and lead to subsequent engine failure. It is
desirable to operate the engine at a temperature as close
as possible to the limit imposed by the oil properties.
Removing too much heat would lower the thermal
efficiency; therefore, the cooling system functions to
remove approximately 35 percent of the heat produced
during combustion.
COOLING SYSTEM CIRCULATION
Six-Cylinder Engine
The water pump discharges coolant into the water jacket
chamber between the front face of the block and the
number one cylinder (Fig. 4). Coolant then flows through
the block, toward the rear, passing through two large cast
openings into the cylinder head, to cool the valve seats,
and forward to the water outlet at the front of the head.
Some coolant is directed through a small hole in the
cylinder head gasket to an area around each spark plug.
During engine warm-up, when the thermostat is closed,
coolant is redirected to the water pump through a
Fig. 3—Water Pump—Typical V-8
THEORY OF OPERATION
coolant by-pass in the cylinder head and block. Coolant
circulation, after normal operating temperatures are
reached (thermostat open), flows through the coolant
outlet and the pellet-type thermostat to the radiator.
Eight-Cylinder Engine
The water pump discharges coolant to each bank of
cylinders. The coolant flow is from the front of each
bank around each cylinder and toward the rear of the
block. Large passages connecting the block to cylinder
head directs coolant over and around the alternately
spaced inlet and exhaust ports, as well as around the
exposed exhaust valve guide inserts. Smaller circular
holes permit metered amounts of coolant to pass from
the cylinder block to cored passages surrounding the
spark plugs.
On "Small V8" engines during warm up (thermostat
closed), coolant is redirected, through a small passage
located in the front of the right cylinder head and block
to a mating hole in the extreme lower portion of the
water pump runner.
On "Mark IV" engines during warm up (thermostat
closed), coolant is redirected to the water pump by way
of a recirculating passage in the intake manifold which
is connected externally to the pump body.
Coolant circulation after normal operating temperatures
are obtained (thermostat open), is directed from the
intake manifold through the coolant outlet and
thermostat to the radiator.
LIGHT DUTY TRUCK SERVICE MANUAL