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Posts Tagged: Brown stain on spark plug

Brown stain on spark plug

Brown stain on spark plug, does it affect spark plug condition? What is the brown stain on spark plug porcelain? The yellow-brown stain on the spark plugs shown here is a “corona” stain. If can be dark brown, light brown, tan or even yellow. The corona stain forms between the metal spark plug shell and the bottom of the spark plug wire or COP coil boot. When a spark plug fires the voltage flow creates static electricity. The static electricity can attract small oil or dirt particles present in the … Read More


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