RADIATOR FAN CLUTCH EMERGENCY SERVICE
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 normal operating range of 175°-195°F (79°-91°C). It is possible,
however, for the thermostat governing fan operation to become damaged. This will result in engine overheating. 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.
Engine coolant temperature exceeds 195°F (91°C) as indicated by engine coolant temperature gauge (3).
Operator has stopped vehicle and allowed engine to idle as described in paragraph 2-16.
Engine coolant temperature gauge (3) indicated engine is not cooling, or engine coolant temperature
continues to rise after two-minute idle period.
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.
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 performed.
Failure to do so may result in fan blade suddenly engaging and cause injury or death.
Do not allow hands to contact engine during emergency service. Burns will result from contact with
Stop engine by shutting off ignition switch (2) and battery switch (1).