Spark plug


  • Inventor
  • Health Benefits
  • degree of heat
  • Characteristics of a used spark plug
  • Spark plug cables

The spark plug was invented in 1903 by Dr. Robert Bosch. The spark plug is one of the most important parts of the ignition system of a petrol or gas engine. Spark plug is the French word for candle.

In order to make an ignition, a high voltage is amplified by the ignition coil to 30.000 volts via the spark plug wire to the spark plug. When the voltage has reached the spark plug, it is conducted through the center electrode or center electrode to the lower part of the spark plug, where the spark plug sits in the combustion chamber. The center electrode is a long pin made of a special material (usually copper so that the heat can be properly dissipated). The end of the spark plug protruding into the combustion chamber is subjected to high temperatures (up to 900 degrees Celsius). Therefore, the tip must be made of a heat-resistant material. The spark that is developed in the spark plug jumps between 2 electrodes. The spark plug should never be bumped or dropped as this may cause the ceramic insulator to malfunction and change the electrode gap. The ceramic insulator is attached to the central electrode (white part where the spark plug is held) to ensure that the spark takes place between the two electrodes. Failure to do so may cause the high voltage or spark to misfire. In that case, the spark plug is defective and must be replaced.

A spark plug consists of 3 parts:

  • Porcelain Insulator
  • Center electrode
  • Spark plug body of metal with a thread and a hexagon, to which one or more ground electrodes are also attached.

Heat Degree:
It is important that the central electrode has the correct temperature. If the temperature is too low, the spark plug will foul and the spark will not jump as well. The temperature should also not be too high, because then it will glow and the mixture will ignite before the spark takes place.

Characteristics of a used spark plug:
A used spark plug can tell the following things about the engine: oil consumption, temperature, ignition timing and operation and fuel consumption.

  • Coffee brown (with milk) is good.
  • Soot deposits indicate too low compression pressure, malfunctioning ignition or too much petrol.
  • When these are wet and smell like petrol, the engine has no correct ignition or incorrect injection quantity (ie a defective ignition coil or injector).
  • Oil deposits indicate oil use in the combustion chamber.
  • White insulator (center of spark plug around electrode) spark plugs are getting too hot.
  • With a hard dry deposit, either the engine or the spark plug will not reach temperature. It is possible that a spark plug with the wrong heat degree has been installed.

Spark plug wires:
Spark plug cables provide the power transfer from the distributor cap or the (DIS) ignition coil to the spark plugs and must not be interchanged. If an engine does not want to start in the morning after a wet night, or the engine runs restlessly in damp weather, damp (leaking) spark plug cables may be the cause.

More information about the type of ignition system or the control of the ignition coil by the ECU can be found on the page ignition system.

error: Alert: Content is protected !!