TM 5-3810-300-24&P-3
5.2.1
The temperature of the engine coolant is automatically
controlled by a thermostat located in a housing
connected to the outlet end of the water manifold. A
blocking type thermostat (Fig. 1) is used when a
standard cooling system is employed; a semi-blocking
type thermostat (Fig. 2) is used with a rapid warm-up
cooling system.
At coolant temperatures below approximately 170F.,
the thermostat valves remain closed and block the flow
of coolant to the radiator, During this period, all of the
coolant in the standard system is circulated through the
engine and is directed back to the suction side of the
water pump via the by-pass tube. In the rapid warm-up
system, enough coolant to vent the system is by-passed
to the radiator top tank by means of a separate external
deaeration line and then back to the water pump without
going through the radiator cores.
As the coolant
temperature rises above 170'F., the thermostat valves
Fig. 2 - Semi-Blocking (Shielded) Type Thermostat
start to open, restricting the by-pass system, and permit
a portion of the coolant to circulate through the radiator.
Remove Thermostat
When the coolant temperature reaches approximately
185'F., the thermostat valves are fully open, the by-pass
1. Drain the cooling system to the necessary level by
system is partially blocked off, and most of the coolant is
opening the drain valve.
directed through the radiator.
2. Remove the bolts which secure the outlet elbow
and the thermostat housing (by-pass tube) to the water
A properly operating thermostat is essential for efficient
manifold (Fig. 1).
operation of the engine.
If the engine operating
temperature deviates from the normal range of 160" to
3. Remove the thermostat and the deflector (if used)
185"F., remove the thermostat and check it.
and clean the seat for the thermostat in the outlet elbow.
Inspect Thermostat
If the action of the thermostat has become impaired due
to accumulated rust and corrosion from the engine
coolant so that it remains closed, or only partially open,
thereby restricting the flow of water, overheating of the
engine will result. A thermostat which is stuck in the
wide open position may not permit the engine to reach its
normal operating temperature, thus resulting in
incomplete combustion of fuel and in build-up of carbon
deposits on the pistons, rings and valves.
The operation of the thermostat may be checked by
Fig. 1 - Typical Thermostat Housing Mounting
immersing it in a container of hot water (Fig. 3). Place a
thermometer in the container, but do not allow it to touch
the bottom of the container. Agitate
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