D379, D398, D399 LOCOMOTIVE ENGINES Caterpillar

Testing Glow Plugs

1. Stop the engine.

2. Disconnect the lead harness wire from the magnetic switch.

3. Connect an ammeter of sufficient capacity between the magnetic switch terminal and the lead harness wire.

4. Push in, turn and hold the HEAT-START switch in the HEAT position.

5. The ammeter reading should be approximately equal to the number of glow plugs multiplied by 5, the approximate amperage used by each glow plug.

A deviation of 5 or more amps from this reading may indicate one or more defective glow plugs.

Locating Defective Glow Plugs

1. Push in, turn and hold the HEAT-START switch in the HEAT position. Observe the ammeter reading.

NOTE: If the ammeter reading does not change, the glow plug was not drawing current when connected and can be assumed to be defective. If the ammeter reading decreases, the glow plug is working properly.

3. Release the HEAT-START switch.

4. Connect the lead to the glow plug.

5. Test each glow plug individually.

Installing Glow Plugs

1. Disconnect the lead wire at the defective glow plug.

2. Remove the defective glow plug.

3. Apply antiseize compound to the threads of the new glow plug.

4. Install the new glow plug and tighten to a torque of 10 to 12 pounds feet.

5. Turn the HEAT-START switch to the HEAT position and observe the ammeter reading.

6. Release the switch.

7. Install the lead wire.

8. Turn the HEAT-START switch to the HEAT position. The reading should be increased. If the reading is the same, check the glow plug wiring.

9. Disconnect the ammeter.