July 11, 2008, Newsletter Issue #123: Spark Plug Foul

Tip of the Week


Generally, most people will associate fouled spark plugs with gas and oil. Although these are two reasons for spark plug fouling, there are other issues you should consider. Every spark plug can foul, no matter how expensive or how good they are. Here are some of the most common reasons for spark plug fouling:

Carbon fouling: Your spark plug will have a black look, and will have soot build up deposits indicating a rich fuel/air mixture, another cause may be from, weak ignition. The carbon based deposits you see on the plug may be conductive, and will allow the voltage coming out of the electrode to travel down the plug instead of jumping the gap. When this happens, you will experience engine misfire. Oil fouling: A black oily spark plug with oil deposits. This fouling indicates advanced engine wear. The cause of this type of foul could be caused by a number of reasons such as worn valve seats or broken piston rings.
Overheating: A spark plug may become overheated for several reasons including incorrect heat range, bad exhaust or exhaust restrictions, like the catalytic converter, or overheating of the engine. The spark plug will be chalky white and sometimes have blisters or discoloration on the spark plug core and or the electrode.
Neglect: Worn out spark plugs. You can see crusty deposits on and around the plug from rust or ash, because the electrode is worn and may appear to be burnt.
There are other reasons for spark plug fouling, though these are the most common. Changing a spark plug will not always help with certain fouling problems. Always use the recommended spark plug gap and heat range. When necessary, make the engine repairs and change spark plugs as indicated by the manufacturer. You can find the recommended time for tune up or spark plug change in your owners manual, or contact any dealership for this information.

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