Spark Plug Diagnosis Chart. Centre andor ground electrodes are rounded and the gap is excessive Cause. The pictures and text are from the Autolite technical manual and just made a bit easier to read in the grand scheme of EZ-Read charts here.
Centre andor ground electrodes are rounded and the gap is excessive Cause. Oil fouled see valves or piston rings White no color on spark plug. A light tangray or brownish color.
SPARK PLUG DIAGNOSIS CHART.
Although there are many different cases if the insulation resistance between the center electrode and the shell is over 10 ohms the engine can be started normally. A light tangray or brownish color. The relief also serves as a pilot guiding a plug straight into the plug hole. Correct heat range for engine ad operating conditions.