HEUI system components (2)

coolant temperature sensor

The engine coolant temperature sensor (1) is located in the front of the right cylinder head. This sensor is used with the ECM to control various functions. The following systems or circuits use the temperature sensor output to the ECM:

  • The Caterpillar Monitoring System Coolant Temperature Gauge over the CAT Data Link
  • The High Coolant Temperature Warning Alert Indicator LED and Gauge on the Caterpillar Monitoring System panel. (The information is transmitted over the CAT Data Link.)
  • The Engine Demand Fan Control, if installed, uses the sensor signal reference to provide the appropriate fan speed.
  • The Cat Electronic Technician (ET) status screen coolant temperature indication.

The coolant flow switch (2) is mounted below the coolant temperature sensor at the inlet to the oil cooler. If the coolant flow stops, the switch will open, causing the coolant flow LED and the action lamp to flash and the action alarm will sound.

fan drive clutch

The 3408E Engine in the D9R is equipped with a variable speed fan drive clutch.

The fan control valve (1) and fan control valve solenoid (2) control fan speed.

The fan drive clutch uses the ECM and temperature sensor as the engine coolant temperature reference. If an electrical failure of the system occurs, the fan will go to maximum rpm.

The advantages of the system are:

  • Reduced fuel consumption in most conditions
  • Reduced engine overcooling at low ambient temperatures
  • Faster engine warm-up
  • More engine power available at the flywheel
  • Reduced noise

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