greenish color. 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. This guide was designed to assist the technician, hobbyist, or race mechanic in understanding, using, and troubleshooting spark plugs. Normal spark plug 10 Good. Carbon fouling . 23 Hot or Lean But OK (?) 11 Good. Spark Plug Colours and Engine Problem Guide Download this sheet as a PDF file here. ... the spark plug will be unable to properly self-clean by burning off carbon deposits. Black is the color of oil fouling. 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. 6 Cold or Rich But OK. 7 Cold or Rich But OK. 8 Cold or Rich But OK. 9 Good. 13 Real Good. 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. Spark plug super clean? 20 Good. 3 Carbon Fouled. 16 Best. Spark Plug Chart for Reference: Here is a spark plug chart showing all the different ways to “read” spark plugs. Head gasket leak causing coolant to steam clean the plug. Follow these instructions on how to remove a spark plug. However, it is nice to know the most important tell-tale signs to look for on spark plugs. Plugs are ideally suited to engine, engine probably in good condition. Heat Range: (click for larger image) Heat Range = Ground Strap, the ground strap indicates the heat-range of the spark plug. 4 Too Cold. Pay more attention to the size of the deposits and where they occur to determine if there is a problem. Cause: Lead additives in fuel. 1 Oil Fouled. 5 Too Cold. Numerous questions have surfaced over the years, leaving many people confused. Spark plugs are one of the most misunderstood components of an engine. Effects: At high loads, the glazing becomes conductive and causes misfiring. Red is a sign of iron particle s or rust in the fuel system. A yellowish color is typically caused by leaded gas. 21 Kinda Hot But OK. 22 Hot or Lean But OK (?) 19 Good. The first step is removing the spark plug you want to look at. A build-up of heavy, light-grey sandy deposits. 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. You will likely see one of the following conditions. This is more of an old-school mechanic test. Spark plug construction. Spark Plugs . 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