Diagnostic Aid for Glow Plugs: The heater element reveals much!
The cause of the failure of a sheathed glow plug can often be found on the heater element. A melted or burnt away heater element points to an injection fault or to a so- called oil burner.
As the injection fault example shows, it is insufficient to only replace the defective plug; the cause of the defect must also be rectified. Here we show you typical damage and the various causes of the damage. Using this diagnostic aid, rapid fault rectification is possible in the majority of cases.
Important note:
On some types of engine, the glow plugs are very difficult to reach. The injection pressure pipes must be partially dismantled and refitted to replace the plugs. Anybody who is not familiar with diesel engines would be well advised to have the glow plugs replaced by a specialist garage!
Heater element with folds and hollows
Causes Open circuit coil due to
- Operation at too high voltage, e.g. on jump starting
- Excessively long current feed due to sticky relay
- Incorrect post-heating with the engine running
- Glow plugs that can be post-heated not used (type GN)
Rectification
- Only jump start with 12 V electrical systems
- Check the pre-heating system, replace automatic pre-heating relay
- Fit glow plugs that can be post-heated
Heater element melted or burnt away
Causes & Overheating of the heater element due to:
- Injection starting too early
- Coked or worn nozzles
- Dripping nozzles
- Engine damage e.g. due to piston seizing, valve damage, etc
- Seized piston ring
Rectification
- Adjust injection timing exactly
- Replace complete injector
Connecting bolt broken off, hex head damaged
Causes
- Connecting bolt broken off: the connecting nut was over tightened
- Damaged hex head: usage of inappropriate tool; due to deformation the plug has a short circuit from the housing to the circular nut.
Rectification
- Use a torque wrench to tighten the connecting nut, tightening torque for M 4 thread: max. 2 Nm, for M5 thread max. 3 Nm; do not oil or grease thread.
- Tighten plug with suitable torque wrench; observe stipulated tightening torque exactly (can also be obtained from the vehicle manufacturer's information). Do not oil or grease thread.
Tip of heater element damaged
Causes - Overheating of the heater element due to
- Injection starting too early resulting in the heater element and heater coil being overheated; the heater coil becomes brittle and breaks.
- Annular gap between plug housing and heater element reduced, as a result too much heat flows from the heater element, the regulator coil remains cold and permits too much current to flow through the heater coil that then overheats.
Rectification
- Check injection system, adjust injection timing exactly.
- On fitting a glow plug, it is imperative that the tightening torque specified by the manufacturer is observed.
Attention:
The threads on all BERU glow plugs are nickel-plated. In this way seizing of the glow plug is reliably prevented. Thus, under no circumstances oil or grease the thread!
