TM-9-2320-272-10
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; OPERATOR'S MANUAL
SEPTEMBER 2004
CHANGE 2
TM-9-2320-272-10 - Page 407 of 481
TM 9-2320-272-10
3-58
3-14. RADIATOR FAN CLUTCH EMERGENCY SERVICE
a. General.
The radiator fan on M939/A1 series vehicles normally activates
when the engine coolant temperature exceeds 185°F (85°C), which is within the nor-
mal operating range of 175°-195°F (79°-91°C). It is possible, however, for the ther-
mostat governing fan operation to become damaged. This will result in engine over-
heating. In an emergency, the operator can bypass the fan thermostat by bolting the
fan to the engine’s fan clutch assembly. This procedure is performed by the operator
only when service by unit maintenance is not available.
b. Symptoms.
(1)
Engine coolant temperature exceeds 195°F (91°C) as indicated by engine
coolant temperature gauge (3).
(2)
Operator has stopped vehicle and allowed engine to idle as described in
paragraph 2-16.
(3)
Engine coolant temperature gauge (3) indicated engine is not cooling, or
engine coolant temperature continues to rise after two-minute idle period.
c. Inspection.
With engine continuing to idle, raise hood and inspect fan (4)
for operation. If fan is not turning, fan clutch thermostat is damaged. Operator
must immediately shut down engine and notify unit maintenance. If service is not
available, perform step d., emergency service.
d. Emergency Service.
WARNING
• Make sure battery switch and ignition switch are OFF. Make
sure crewmembers inside vehicle cab are aware of danger in
engaging these switches while emergency service is being per-
formed. Failure to do so may result in fan blade suddenly engag-
ing and cause injury or death.
• Do not allow hands to contact engine during emergency service.
Burns will result from contact with engine.
(1)
Stop engine by shutting off ignition switch (2) and battery switch (1).
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