TM 9-2320-272-24-1
1-21. POWER SYSTEM OPERATION (Contd)
Key Item and Function
SURGE TANK - Filling point for cooling system. On M939A2 vehicles, a float sensor monitors water
1
level and illuminates a light on instrument panel.
COOLANT PRESSURE CAP - Designed to depressurize cooling system and to access cooling
2
system for tilling.
WATER MANIFOLD - Collects coolant from cylinder heads and directs it to thermostat housing
3
(M939/A1 series only).
4
SURGE TANK-TO-WATER MANIFOLD VENT - Vents air trapped in water manifold (M939/A1
series only).
5
SURGE TANK-TO-RADIATOR VENT - Vents air in cooling system.
6
THERMOSTAT - Shuts off coolant flow to radiator until temperature reaches 175F (79C) on
M939/A1 series vehicles and 181F (83C) on M939A2 series vehicles. Coolant is then directed to the
radiator through the radiator inlet hose.
RADIATOR INLET HOSE - Directs coolant from water manifold to radiator after thermostat has
7
opened.
BYPASS TUBE - Directs coolant back to transmission oil cooler, where it is then recirculated
8
through the engine block until the thermostat opens.
RADIATOR SHROUD - Concentrates air flow through the radiator.
9
RADIATOR - Directs coolant through a series of fins or baffles so outside air can remove excessive
10
heat from coolant.
FAN CLUTCH - Regulates use of fan to control engine temperature fan to belt-driven pulley when
11
conditions require additional cooling.
WATER PUMP - Provides force to move coolant through engine.
12
FAN - Provides force to pull air through radiator.
13
RADIATOR DRAINVALVE - Permits coolant to be drained from radiator.
14
TRANSMISSION OIL COOLER HOSE - Directs coolant to transmission oil cooler.
15
ENGINE OIL COOLER - Reduces heat of engine oil (M939/A1 series only).
16
TRANSMISSION OIL COOLER - Reduces heat of transmission oil.
17
ENGINE OIL COOLER-TO-HEATER HOSE - Directs coolant to personnel water heater when
18
shutoff valve is open (M939/A1 series only).
PERSONNEL WATER HEATER - Provides heat for cab and personnel (M939/A1 only).
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