The heat rating indicates the degree of maximum permissible thermal load of one spark plug. As the heat rating decreases, the permissible thermal load increases. In this case, heat dissipation from the spark plug improves, which reduces the risk of pre-ignition (engine operation after ignition off). The main disadvantage of spark plugs with a high thermal load rating is that the self-cleaning temperature of the spark plug is also high. In this case, the working part of the spark plug becomes covered with deposits, especially when the engine does not warm up to operating temperature while driving.
The glow number of the spark plug is specified by the car manufacturer. Spark plugs differ from each other by the presence of one or more side electrodes and the diameter and length of the thread, so for normal operation of the engine it is necessary to use only the spark plugs prescribed by the manufacturer.
The service life of spark plugs is mainly determined by the material of the electrodes. Electrodes made of chromium-nickel alloy have high thermal conductivity and high corrosion resistance. The use of silver provides maximum thermal conductivity. Platinum electrodes have the highest anti-corrosion qualities and resistance to fading. The service life of spark plugs depends on the electrode material used and the design of the spark plugs and ranges from 20,000 to 100,000 km.
Two types of seals are used between the spark plug and the cylinder head.
If the spark plug has a flat sealing surface, a non-removable outer sealing ring is installed on the spark plug. If the spark plug has a conical seal, no additional sealing rings are required. Due to the reduction in engine dimensions, spark plugs with a flat seal and a reduced spanner size or spark plugs with a conical seal are used.
[The original article is available at VWManual.ru]
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