When there is overheating, the insulator surface of the spark plug becomes pure white and the burning gases deposit spots. Electrode melting is a more advanced type of overheating and when spark plug temperatures reach 800¡ãC or more, the tip of the plug may glow red hot and become a source of ignition prior to sparking, causing abnormal combustion that can damage the engine.
Overheating
Causes of Overheating and corrective actions