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TM 10-3930-633-12
Section XII. MAINTENANCE OF COOLING SYSTEM
4-63. General
The thermostat is a heat-operated valved. It
should always be maintained in working order
a. The cooling system is of the pressurized
and the vehicle should never be driven without
type and utilizes a tube and fin type radiator. The
one installed, as there would then be no control of
coolant is drawn from the bottom of the radiator
engine temperature. The temperature at which
by the water pump, which circulates the coolant
the thermostat opens is preset and cannot be
through the engine block. As the coolant enters
altered.
the block, it travels through cored passages to
d. Thermostat Test and Replacement. When
cool the entire length of each cylinder wall. Upon
the thermostat is not operating properly, the
reaching the rear of the cylinder block, the coolant
engine may run too hot or too cold. Overheating
is directed upward into the cylinder head where it
may damage the thermostat so that its valve will
cools the combustion chambers, valves and valve
not function properly, and a cold engine will not
seats on its return to the front of the engine.
achieve full efficiency. Rust can also interfere
b. At the front of the engine, the coolant flows
with thermostat operation. To test the ther-
into the coolant outlet connection, past the
mostat, place it in water heated approximately
thermostat if it is open, and into the top radiator
250 F. (17 C.) above the temperature stamped on
header tank. If the thermostat is closed, a small
the thermostat valve. Submerge the bellows
portion of the coolant is returned to the water
completely and agitate the water thoroughly. The
pump for recirculation. The entire system is
valve should open fully. Next, place the ther-
pressurized at 12-15 PSI.
mostat in water heated approximately 100 F. (11 0
4-64. Hoses and Thermostat
C.) below the temperature stamped on the
a. Inspection of Hoses. Air, heat, and water
thermostat valve. Submerge the bellows com-
deteriorate radiator hoses in two ways: by hard-
pletely and agitate the water thoroughly. The
ening or cracking which destroys flexibility and
valve should close completely. If the thermostat
causes leaks; by softening and swelling which
fails either of these tests, it should be replaced
produces lining failure and hose rupture and
with a new one of the same type and rating.
clogging. Examine hoses spring and fall for
KEY to fig. 4-33:
possible need of replacement or tightening. If
1. Clamp
hoses are collapsed, cracked, or indicate a soft
2. Upper hose
condition on the inside, they should be replaced.
3. Screw
b. Replacement of Hoses. Refer to figure 4-33
4. Water outlet elbow
5. Clamp
for parts relationship of cooling system parts.
6. Cap
When installing a new hose, clean the pipe
7. Gasket
connections and apply a thin layer of nonhard -
8. Thermostat
ening sealing compound. Hose clamps should be
9. V-belt set
10. Clamp
properly located over the connections to provide
11. Lower hose
secure fastening. The pressurized cooling system
12. Drain cock
pressure can blow off improperly installed hoses.
13. Radiator cap
c. Thermostat. The cooling system of the
14. Screw
15. Nut
engine is designed to provide adequate cooling
16. Rubber mount
under most adverse conditions. However, it is
17. Washer
necessary to employ some device to provide quick
18. Washer
warming and to prevent overcooking during
19. Washer
normal operation. Automatic control of engine
20. Band strap
21. Radiator
operating temperature is provided by a water flow
control thermostat installed in the water outlet.

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