ISM, ISMe, and QSM11 – 008-027   Fan Clutch, On-Off

The fan clutches can be controlled by the electronic control module (ECM). The ECM is programmed to turn the fan on when 0-VDC (normally open switch) is applied to the fan clutch relay, and turn the fan off when 12-VDC (normally closed switch) is applied to the fan clutch relay.

The following fan clutch checks are for fan clutches wired to the electronically controlled fuel system. Refer to the OEM service manual to determine the correct installation of the fan clutch.

Remove the shutter stat from the thermostat housing, if equipped, and install a master temperature gauge that is known to be accurate. A thermocouple can be used.

Restrict the radiator’s airflow.

Operate the engine at rated rpm.

If the vehicle is air-conditioned, make sure the air-conditioning is turned off to prevent continuous operation of the fan. When the coolant temperature reaches 96°C [205°F], check for fan engagement.

The temperature given for fan engagement is for fans controlled by the ECM.

Fan noise and airflow increase when the fan clutch engages.

Return the engine to idle, and remove the radiator air restriction.

The fan clutch must disengage before the coolant temperature drops to 93°C [200°F]. Cummins Inc. recommends the fan disengage at 3°C [6°F] below the temperature stamped on the fan temperature sensor.

The temperature given for fan disengagement is for fans controlled by the ECM.

Remove the temperature gauge or thermocouple, and install the shutter stat, if used.