Insufficient engine cooling or lubrication.Continuous driving under excessively heavy load.Fuel octane rating too low (knock is present).Insufficient tightening torque and/or no gasket.If the selected spark plug heat range is too cold, the spark plug may begin to foul when the engine speed is low or when operating in cold conditions with rich air-fuel mixtures. In some cases, the insulator nose can usually be cleaned by operating the engine at higher speeds in order to reach the self-cleaning temperature. If the spark plug has completely fouled, and the engine will not operate correctly, the spark plug may need to be replaced and the fouling cause identified. Carbon deposits will begin to burn off from the insulator nose when the self-cleaning temperature is reached. When the heat range is too cold for the engine speed, the firing end temperature will stay below 450☌ and carbon deposits will accumulate on the insulator nose. This is called carbon fouling. When enough carbon accumulates, the spark will travel the path of least resistance over the insulator nose to the metal shell instead of jumping across the gap. This usually results in a misfire and further fouling. Reduced compression and oil usage due to worn piston rings/cylinder wallsĬarbon fouling occurs when the spark plug firing end does not reach the self-cleaning temperature of approximately 450☌ (842☏).Continuous low-speed driving and/or short trips.The heat range must be carefully selected for proper spark plug thermal performance. If the heat range is not optimal, then serious trouble can be the result. The optimal firing end temperature is approximately 500☌ (932☏) to 800☌ (1472☏). The two most common causes of spark plug problems are carbon fouling ( 800☌). A colder spark plug functions in an opposite manner. The insulator nose of a hotter spark plug also has a greater surface area that is exposed to more of the ignited gases and is easily heated to higher temperatures. Therefore, the path for the dissipation of heat from the insulator nose to the cylinder head is longer and the firing end stays hotter. The insulator nose of a hotter spark plug has a longer distance between the firing tip of the insulator and the point where insulator meets the metal shell. A hot-type spark plug has a longer insulator nose. The major structural difference affecting the heat rating is the length of the insulator nose. Relative position of the insulator tip to the end of the shell (projection).Structure of the center electrode such as a copper core, etc.
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