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Join Date: Jul 2008
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Generally, hotter spark plugs are used in an engine that is running rich or uses oil. The hotter plug burns the contamination off and keeps the plugs from fouling.
Any soot around the base of the plug is just that. It does not indicate the running condition of the engine. What you should be concerned with is the condition of the electrode tip and the surrounding insulator.
A grayish tan to while color on the insulator and tip indicates the correct spark plug is in use, the fuel and ignition systems are in good shape and overall engine mechanical condition is good. Soft, black, sooty, dry-looking deposits on the tip and insulator indicate a rich air fuel mixture, weak ignition or wrong heat range spark plug (too cold). That is when you would consider changing to a hotter spark plug.
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