Aquí dejo explicación de lo que podría pasar si no se elige heat range correcto.
http://www.ngksparkplugs.com/about-n...rk-plug-basics
En tu caso, que actualmente tiene heat range 20, mas fría. Lo que podría pasar es:
"Pre-delivery fouling:
Carbon fouling occurs when the spark plug firing end does not reach the self-cleaning temperature of approximately 450°C (842°F). 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°C 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.
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."
Si el rango de calor de la bujía seleccionado es demasiado frío, la bujía puede comenzar a ensuciar cuando la velocidad del motor es baja o cuando funciona en condiciones frías con mezclas ricas de combustible y aire. En algunos casos, la punta del aislador generalmente puede limpiarse haciendo funcionar el motor a velocidades más altas para alcanzar la temperatura de autolimpieza. Si la bujía se ha ensuciado completamente y el motor no funciona correctamente, es posible que se deba reemplazar la bujía y se haya identificado la causa del ensuciamiento.