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TM 5-4210-220-12
1-14. ENGINE COOLING SYSTEM - Continued
b. Fan and Shutters The ambient air flow through the radiator removes heat from the coolant circulated through
the core. To maintain optimum engine operating temperature, the air flow is controlled. The shutters and fan providing
this control are automatically engaged by the multistat, (see fig. 1-23). When the engine is started, compressed air is
provided to close the shutters and to disengage the fan clutch. With the fan not operating and no flow of ambient air
through the radiator the cooling system heats up rapidly. When the coolant reaches operating temperature the multistat
shuts off air pressure to the shutter cylinder. This causes the shutters to open. When the flow of air through the radiator
is insufficient to dissipate the heat, the multistat shuts off air pressure to the fan clutch and it engages. Increased
ambient air flow through the radiator thereby reduces the coolant temperature. The system temperature is maintained
within a range of 5 to 6 deg. F (2.5 deg. to 3 deg. C). The automatic control of the fan and shutters can be manually
disengaged by an override control provided in the cab. When operated, air flow to the multistat is shut off, thus the
shutters are open and the fan engaged.
Figure 1-23. Radiator Fan and Shutter System
1-31
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