TM-9-2320-272-24-1
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; UNIT, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE MANUAL; VOLUME 1 OF 4
JUNE 1998
TM-9-2320-272-24-1 - Page 51 of 1015
TM 9-2320-272-24-1
1-21. POWER SYSTEM OPERATION (Contd)
Key Item and Function
1
SURGE TANK
- Filling point for cooling system. On M939A2 vehicles, a float sensor monitors water
level and illuminates a light on instrument panel.
COOLANT PRESSURE CAP
- Designed to depressurize cooling system and to access cooling
system for tilling.
WATER MANIFOLD
- Collects coolant from cylinder heads and directs it to thermostat housing
(M939/A1 series only).
SURGE TANK-TO-WATER MANIFOLD VENT
- Vents air trapped in water manifold (M939/A1
series only).
SURGE TANK-TO-RADIATOR VENT
- Vents air in cooling system.
THERMOSTAT
- Shuts off coolant flow to radiator until temperature reaches 175°F (79°C) on
M939/A1 series vehicles and 181°F (83°C) 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
opened.
BYPASS TUBE
- Directs coolant back to transmission oil cooler, where it is then recirculated
through the engine block until the thermostat opens.
RADIATOR SHROUD
- Concentrates air flow through the radiator.
RADIATOR
- Directs coolant through a series of fins or baffles so outside air can remove excessive
heat from coolant.
FAN CLUTCH
- Regulates use of fan to control engine temperature fan to belt-driven pulley when
conditions require additional cooling.
WATER PUMP
- Provides force to move coolant through engine.
FAN
- Provides force to pull air through radiator.
RADIATOR DRAINVALVE
- Permits coolant to be drained from radiator.
TRANSMISSION OIL COOLER HOSE
- Directs coolant to transmission oil cooler.
ENGINE OIL COOLER
- Reduces heat of engine oil (M939/A1 series only).
TRANSMISSION OIL COOLER
- Reduces heat of transmission oil.
ENGINE OIL COOLER-TO-HEATER HOSE
- Directs coolant to personnel water heater when
shutoff valve is open (M939/A1 series only).
PERSONNEL WATER HEATER
- Provides heat for cab and personnel (M939/A1 only).
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