Posts Tagged: Brown stain on spark plug

What Causes Brown Stains on Spark Plugs

Understanding the Yellow-Brown Stain on Spark Plugs The yellow-brown stain on spark plugs is a “corona” stain. It 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 attraction and heats bonds the particles … Read More