spark plug is over-torqued into an aluminum head, the aluminum threads begin to “roll over,” causing a high degree of friction when the spark plugs are removed. In worst-case scenarios, the threads actually separate or strip from the cylinder head casting and may require removal of the cylinder head to repair. In other cases, over-torquing a spark plug can distort and break the seal between the metal shell and porcelain insulator, which causes combustion gases to leak into the spark plug boot and blow it off the spark plug. If a spark plug boot keeps blowing off, suspect a seal leak caused by an over-torqued spark plug.








[Appearance]
Brown deposits on the insulator directly above the housing
[Results]
No impact on the spark plug performance
[Cause]
This occurs due to electrical stress in the air near the insulator. (This is not a spark plug gas leak, for which it is sometimes mistaken.)