TM 5-3895-359-14&P
THERMOSTAT
The temperature of the engine coolant is automatically
water to form sulfuric acid. Therefore, install a
controlled by a thermostat located in a housing
180or 190F (82or 88C) temperature thermostat
connected to the outlet end of the water manifold. A
and modify the cooling system to provide rapid
blocking type thermostat (Fig. 1) is used in the standard
warm-up in order to maintain coolant temperature
cooling system.
at a minimum of 175F (80C).
Operation
Remove Thermostat
At coolant temperatures below approximately 160 to
1. Drain the cooling system to the necessary level by
170F (71 to 77C), the thermostat valves remain
opening the drain valve.
closed and block the flow of coolant to the radiator.
2. Remove the bolts which secure the outlet elbow and
During this period, all of the coolant in the standard
the thermostat housing (bypass tube) to the water
system is circulated through the engine and is directed
manifold (Fig. 1).
back to the suction side of the water pump via the
bypass tube. As the coolant temperature rises above
3. Remove the thermostat and clean the seat for the
160 to 170 F (71 to 77 C) the thermostat valves start
thermostat in the outlet elbow.
to open, restricting the bypass system, and permit a
portion of the coolant to circulate through the radiator.
4. Remove and discard the seals pressed in the water
outlet elbow.
When the coolant temperature reaches approximately
185 to 195F (85 to 91C) the thermostat valves are
Inspection
fully open, the bypass system is partially blocked off,
and most of the coolant is directed through the radiator.
If the action of the thermostat has become impaired due
to accumulated rust and corrosion from the engine
A properly operating thermostat is essential for efficient
coolant so that it remains closed, or only partially open,
operation of the engine.
If the engine operating
thereby restricting the flow of coolant, overheating of the
temperature deviates from the normal range of 160 to
engine will result. A thermostat which is stuck in the
185F (71to 85C) or 170 to 195F (77 to 91C),
wide open position may not permit the engine to reach
remove the thermostat and check it.
its normal operating temperature.
The incomplete
combustion of fuel due to cold operation will result in
CAUTION: There are areas where
build-up of carbon deposits on the pistons, rings and
approved fuel (less than 0.5% sulfur)
valves.
is not commercially available or
economically feasible to obtain. It is
Check the operation of a thermostat as follows:
important to keep the engine cooling
1. Immerse the thermostat in a container of water (Fig.
system temperature of these engines
on the high side of normal to prevent
the condensation of sulfur trioxide
2. Place a thermometer in the container using care not
gas,
which
combines
with
to allow the thermometer to touch the bottom or sides of
the container.
3. While slowly agitating the water to maintain an even
temperature, apply heat to the container. As the water
is heated, the thermostat should begin to open (the
opening temperature is usually stamped on the
thermostat). The thermostat should be fully open at
approximately 185 - 195F (85-91 C). Allow at least
10 minutes for the thermostat to react.
Fig. 1 - Typical thermostat Housing Mounting
(Radiator Cooling System)
10-6-11
