Trooper LS V6-3.5L (1998)
Cracked or broken insulators may be the result of improper installation, damage during spark plug re-gapping, or heat shock to the insulator material.
Upper insulators can be broken when a poorly fitting tool is used during installation or removal, when the spark plug is hit from the outside, or is
dropped on a hard surface. Cracks in the upper insulator may be inside the shell and not visible. Also, the breakage may not cause problems until oil or
moisture penetrates the crack later.
A broken or cracked lower insulator tip (around the center electrode) may result from damage during re-gapping or from "heat shock" (spark plug
suddenly operating too hot).
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Damage during re-gapping can happen if the gapping tool is pushed against the center electrode or the insulator around it, causing the insulator to
crack. When re-gapping a spark plug, make the adjustment by bending only the ground side terminal, keeping the tool clear of other parts.
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Heat shock" breakage in the lower insulator tip generally occurs during several engine operating conditions (high speeds or heavy loading) and
may be caused by over-advanced timing or low grade fuels. Heat shock refers to a rapid increase in the tip temperature that causes the insulator
material to crack.
Spark plugs with less than the recommended amount of service can sometimes be cleaned and re-gapped then returned to service. However, if there is
any doubt about the serviceability of a spark plug, replace it. Spark plugs with cracked or broken insulators should always be replaced.
