Quote:
Originally Posted by ssgm1x
Can anyone tell me why these plugs have a black spot on them ?
2018 F80 M3 with NGK 97506 plugs that are only 1-2 months old running full E85 (measured E80)
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I used NGK 97506 for a while and they look exactly the same as yours, with only 3000km on them. I have changed them back to stock plug.
Check this up:
http://4secondsflat.com/Spark_plug_reading.html
This occurs for two reasons, excessive idling or rich idle condition leaving heavy soot deposits. These deposits will burn and create excessive porcelain temps causing the glass to melt usually resulting in a down track popping through the exhaust..
You will usually see splotchy deposits on the plugs after the run, either green or yellow in color and of course the tell tale shiny glaze. This glazing of the porcelain actually becomes a conductor and the spark will jump from the electrode to the porcelain resulting is a very weak small if any spark. The porcelain should always have a chalky or dull finish.