Posts Tagged: Brown stain on spark plug

Brown stain on spark plugs — What’s the Cause and Is It a Problem?

The brown stain on spark plugs is normal and doesn’t affect plug operation The yellow-brown stain on spark plugs 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 spark plug well or out in the open air. The … Read More