Look at the firing tip of your spark plugs while paying close attention to the condition and color of the ceramic insulator and the metal electrodes (known as the center wire and ground wire). If you have access to an Autolite® Master Catalog, you will find a series of pictures on the inside back cover to compare your spark plugs to. If not, simply observe the color first. Light tan or gray deposits are normal, and an indication that everything is working well. If everything is very white, with glazed deposits on the insulator tip, the spark plug is too hot for the engine, or at least for the conditions for which it was used. If black sooty deposits are present, a too rich fuel mixture is likely, or the spark plugs' heat range may be too cold for the application. Shiny black or oily deposits are an indication of bad oil seals and/or piston rings, and are not an indication that the spark plugs are at fault. Click here for more information. Let our technicians help you at Autolite Answers(SM). 855-200-5200