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 TM 55-1905-219-14-5
3-78.
THERMOSTAT AND HOUSING - MAINTENANCE INSTRUCTION.
a. The temperature of the engine coolant is automatically con- trolled by a thermostat located in the
housing connected to the outlet end of the water manifold and to the heat exchanger (expansion tank).
b. At coolant temperatures below approximately 170 (76.7 ), the thermostat valves remain closed
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and block the flow of coolant to the heat exchanger (expansion tank). During this period, all of the coolant is
circulated through the engine and is directed back to the suction side of the water pump via the by-pass tube.
As the coolant temperature rises above 170 (76.7 ), the thermostat valves start to open, restricting the by-
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pass system, and permit a portion of the coolant to circulate through the heat exchanger (expansion tank).
When the coolant temperature reaches approximately 185 (85 ), the thermostat valves are fully open, the
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by-pass system is partially blocked off, and most of the coolant is directed through the heat exchanger
(expansion tank).
c. A properly operating thermostat is essential for efficient operation of the engine. If the engine
operating temperature deviates from the normal range of 160 to 185 (71 to 85 ) remove the themostat
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and check it.
d. The by-pass hoses and tubes of the water and exhaust manifold help to by-pass the thermostat while
the engine is warming up.
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