Pontiac FIREBIRD 1972 Service Manual page 630

6A-10 1972 PONTIAC SERVICE MANUAL
Fig. 6 A - 1 2 Fluid Clutch Fan Assembly
The clutch coil is calibrated so that with a road load at an
ambient temperature of approximately 90°F., the clutch is
just at a point of shift between high and low fan speed.
No attempt should be made to disturb the calibration of
the engine clutch fan assembly as each assembly is in-
dividually calibrated at the time of manufacture.
Under certain temperature conditions there is an apparent
lateral movement at the fan tip which should not be con-
sidered as a hub or bearing failure. This condition is a
design feature of the clutch assembly which allows up to
approximately 1/4" lateral movement measured at the fan
tip.
NOTE: Testing a clutch fan by holding the
small hub with one hand and rotating the
aluminum housing in a clockwise/counter-
clockwise motion will cause the clutch to free-
wheel which is a nonnal condition when ope-
rated in this manner. This should not be
considered a test by which replacement is deter-
mined.
A pellet-type thermostat is used in the water outlet pas-
sage to control the flow of coolant, providing fast engine
warm-up and regulating coolant temperatures (Fig. 6A-
13). A wax pellet or power element in the thermostat
expands when heated and contracts when cooled. The
pellet is connected through a piston to a valve and, when
the pellet is heated, pressure is exerted against a rubber
diaphragm which forces the valve to open. As the pellet
is cooled, the contraction allows a spring to close the
valve. Thus, the valve remains closed while the coolant is
cold, preventing circulation of coolant through the radia-
tor but allowing the coolant to circulate throughout the
engine to warm it quickly and evenly.
As the engine becomes warm, the pellet expands and the
thermostat valve opens, permitting the coolant to flow
through the radiator where heat is passed through the
radiator walls. This opening and closing of the thermostat
valve permits enough coolant to enter the radiator to keep
the engine within specified temperature limits.
Engine thermostat control temperatures vary as coolant
mixtures vary; therefore, a 195°F. thermostat is installed
as standard equipment and is used with glycol-type coo-
lant.
NOTE: Higher temperature thennostats will
not provide faster wann-up, since their valves
remain tightly closed until the control tempera-
tures are reached, as does a lower temperature
thermostat.
COOLING SYSTEM CIRCULATION
8 CYLINDER
Water circulation is provided by a single impeller, spe-
cially designed water pump which provides a balanced
flow of water into each bank of the cylinder block.
Water circulation during warm-up (thermostat closed) is
from pump to each bank of cylinder block, up into cylin-
der heads, into front of intake manifold and back to inlet
of pump via an internal recirculation passage connecting
the intake manifold and timing chain cover which acts as
pump body (except 307 engine).
On the 307 engine, coolant is routed past the thermostat,
via a by-pass hose, directly into the water pump.
Water circulation after normal operating temperatures are
reached (thermostat open) takes two courses. Part of the
FLANGE PISTON
~ ~
FLANGE SEAL
I
WAX PELLET RUBBER DIAPHRAGM
Fig. 6A-13 Pellet-Type Thermostat