DENSO W20EX-U Toyota Spark Plugs Removable Cap 90999-09007 White

Overheating
Insulator skirt side was”blach white”shaped electrode ablation prematurely. Because premature ignition timing,cooling system adverse; using a low-grade gasoline, mixture too lean; spark plug into the combustion chamber and spark plug heat value too low; spark plug installation torque is not enough, the outer seal leak worse.

Insulator breakage
End of the spark plug insulator skirt cracking or breakage.The use of low-grade gasoline or cause premature ignition timing.

Oil wet
Hulled face screwed around and luminal surface portion of the insulator and the electrode surface adhesion side skirts with black wet shiny oil.Mainly piston rings, cyclinder wear