GMC 1976 ZEO 6083 Maintenance Manual page 333

6K- 2 ENGINE COOLING
Figure 2-Coolant Recovery Reservoir Type I
the reservoir will be drawn back to the radiator
through the vent valve. In this manner, the radiator
will keep itself full at all times. The need for addi-
tional coolant can be detected by observing the level
of coolant in the reservoir at the "COLD" level line
the engine is cold .
In vehicles equipped with a "Coolant Level" in-
dicator system, the indicator light is designed to glow
when additional coolant is required . For service and
diagnosis of "Coolant Level" indicator system, refer
to CHASSIS ELECTRICAL (SECTION 12).
COOLING SYSTEM CIRCULATION
(FIGURE 4)
The coolant is circulated by a centrifugal pump
mounted on the front engine cover which forms the
outlet side of the pump. The engine fan and pulley(s)
are bolted to the pump shaft hub at its forward end.
Thus both the fan and pump are belt driven by a
crankshaft pulley bolted to the harmonic balancer .
The pump shaft and bearing assembly is pressed in
the water pump cover. The bearings are permanently
lubricated during manufacture and sealed to prevent
loss of lubricant and entry of dirt . The pump is sealed
against coolant leakage by a packless non-adjustable
seal assembly mounted in the pump in position to
bear against the impeller hub. The inlet pipe cast in
the pump body feeds into the passage formed by the
cover and the front face of the impeller, which is
Figure 3-Coolant Recovery Reservoir, Type II
mounted on the bearing shaft with the vanes facing
forward. Coolant flows through the inlet passage to
the low pressure area at the center where it then
flows radially through six openings in the impeller .
Vanes on the rotating impeller cause the coolant to
flow rearward through two discharge passages cast
in the engine block. These passages deliver an equal
quantity of coolant to each cylinder bank water
jacket .
The coolant then flows rearward through the wa-
ter jacket which surrounds each cylinder barrel and
extends below the lower limit of piston ring travel .
After flowing the full length of the cylinder banks,
the coolant flows up through openings to the rear of
the cylinder bank into the cylinder heads. The coo-
lant flows forward in the cylinder heads to cool the
combustion chamber areas.
Next, the coolant flows into the intake manifold
water passage from the forward port of the cylinder
heads to the thermostat housing and thermostat by
pass . A nipple in the pump body allows connection
of the heater hose.
A pellet type thermostat housed in the forward
(outlet) end of the intake manifold controls the circu-
lation of water through the engine radiator . During
cold engine operation when the thermostat is closed,
a thermostat by-pass, open at all times, allows recir-
culation of coolant through the engine to provide
rapid warm-up. When the thermostat opens, (195°F.,
90 .6°C.) coolant is directed to the left tank of the
radiator, through the radiator core and right tank to
the water pump inlet where the cycle is repeated .