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Thanks to copper (CU), and even more so for the silver central electrode, the thermal conductivity increases, and hence the heat resistance. The advantages of plugs with platinum center electrodes are easier sparking, as well as less wear and a wide temperature range.
The value of the glow number recommended by the manufacturer can only be deviated from if the operating conditions differ significantly from normal and malfunctions occur. If the spark plugs are constantly covered in soot, i.e. they do not reach their self-cleaning temperature (when traveling short distances), then it is recommended to replace them with candles with the next higher glow number. If the engine is operated exclusively at full throttle, it is recommended to replace the spark plugs with spark plugs with the next lower glow number.