Troubleshooting:

Causes Of Sheathed Glow Plug Failure And Solutions

A diesel engine will start in warm and dry weather even if a glow plug is defective and only the other plugs pre-glow. Although the start is usually accompanied by an increased emission of pollutants and sometimes shuddering, the driver will not consciously notice these signs or may be unable to interpret them correctly. The nasty surprise then comes when it is cold or damp and the first night’s frost arrives: The "source of heat" in the diesel engine no longer functions and at best it will start poorly and smoke -although it is more probable that nothing will start.

The following indicates typical damage and lists the various causes. This diagnostic aid guarantees a speedy remedy in most cases.

Heating rod with folds and dents

Causes:
Break in the spiral caused by

1. Operation with excessive voltage, e.g. with a starter aid
2. Current applied too long by suspended relay
3. Forbidden afterglow while engine is running
4. Use of a non-afterglow-compatible glow plug

Possible Solutions:

1. Use starter aid with 12-Volt on-board network.
2. Check pre-glow system.
3. Replace glow time relay.
4. Install afterglow-compatible glow plug.

 

Heating rod melted, melted through or broken

Causes:
Overheating of the heating rod due to

1. Premature start of injection
2. Nozzles blocked or clogged with soot
3. Engine damage, e.g. due to piston corrosion or valve
   breakage, etc.
4. Dripping nozzles
5. Piston rings blocked or stuck

Possible remedies:

1. Set injection time precisely.
2. Clean injection nozzles.
3. Check jet profile.

Connecting bolt broken, hexagonal bolt damaged

Causes:

1. Break in connecting bolt: The current connecting nut was
   tightened with excessive torque.
2. Damaged hexagonal bolt: Use of incorrect tools; the deformation of the plug creates a short-circuit between the
   housing and the round nut.

Possible remedies:

1. Tighten the current connecting nut with the torque spanner.
   Adhere to the tightening torque. Neither grease nor lubricate the thread.
2. Tighten the plug with a suitable torque socket spanner. Adhere exactly to the specified tightening torque (this can be seen in vehicle manufacturer regulations).

 

Tip of heating rod damaged

Causes:
Overheating of the heating rod due to

1. Premature start of injection, which overheats the heating
   rod and heating coil; the heating coil becomes brittle and breaks.
2. Closed ring gap between the plug housing and the heating rod; too much heat dissipates out of the heating rod as a result,
3. The regulating coil remains cold and allows too much current pass into the heating coil, which overheats.
   

Possible remedies:

1. Check injection system, set the injection time precisely.
2. Adhere to the tightening torque specified by the manufacturer when screwing in the glow plug.

Top