The first step is removing the spark plug you want to look at. Dry, black, soot-like deposits. Black is the color of oil fouling. 3 Carbon Fouled. Cause: Lead additives in fuel. Pay more attention to the size of the deposits and where they occur to determine if there is a problem. You will likely see one of the following conditions. This guide was designed to assist the technician, hobbyist, or race mechanic in understanding, using, and troubleshooting spark plugs. 21 Kinda Hot But OK. 22 Hot or Lean But OK (?) 6 Cold or Rich But OK. 7 Cold or Rich But OK. 8 Cold or Rich But OK. 9 Good. Spark Plugs . ... the spark plug will be unable to properly self-clean by burning off carbon deposits. Heavy deposits . Normal spark plug This is more of an old-school mechanic test. 11 Good. Note the brown to greyish tan color, and minimal amount of electrode erosion which clearly indicates the plug is in the correct heat range and has been operating in a "healthy" engine. 18 Good. 23 Hot or Lean But OK (?) Look at end of the spark plug that was in the cylinder and examine it. Below we share the spark plug reading chart: Normal Condition An engine’s condition can be judged by the appearance of the spark plug’s firing end.If the firing end of a spark plug is brown or light gray,the condition can be judged to be good and the spark plug is functioning optimally. Carbon fouling . 15 Best. A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed petrol by means of an electric spark. Caused by rich running. 5 Too Cold. 19 Good. Follow these instructions on how to remove a spark plug. 12 Good. Spark plug super clean? Spark plug heat range and color chart NORMAL Combustion deposits are slight and not heavy enough to cause any detri***** effect on engine performance. 1 Oil Fouled. A yellowish color is typically caused by leaded gas. Numerous questions have surfaced over the years, leaving many people confused. Often caused by worn valve guides, excessive use of upper cylinder lubricant, or idling for long periods. 2 Oil Fouled. Spark Plug Chart for Reference: Here is a spark plug chart showing all the different ways to “read” spark plugs. Take the spark plug in your hand and begin looking at it for signs of damage. 13 Real Good. Spark plugs are one of the most misunderstood components of an engine. Spark Plug Colours and Engine Problem Guide Download this sheet as a PDF file here. Glazing results from high engine loading after extended part-load operation. 16 Best. 17 Best. Head gasket leak causing coolant to steam clean the plug. However, it is nice to know the most important tell-tale signs to look for on spark plugs. greenish color. Effects: At high loads, the glazing becomes conductive and causes misfiring. 14 The Best. Plugs are ideally suited to engine, engine probably in good condition. Lead fouling Insulator nose covered in places with thick brown/yellow glazing, which can have a greenish color. 4 Too Cold. Heat Range: (click for larger image) Heat Range = Ground Strap, the ground strap indicates the heat-range of the spark plug. With help from the spark plug experts at NGK, we’ll teach you how to diagnose minor tuning issues or potentially major engine problems by examining your spark plugs.Check out the images below, courtesy of NGK Spark Plugs, and get ready to do a little light reading the next time you pull your spark plugs.. Normal. A build-up of heavy, light-grey sandy deposits. 10 Good. 20 Good. Remedy: Replace with new spark plugs. Spark plug construction. 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