Chevy Spark Plug Problems


Spark plugs are one of the most important components within any Chevrolet engine, as they are responsible for igniting the air/fuel mixture. Not all spark plugs are manufactured the same way because not every Chevrolet engine is designed the same way. Spark plugs operate under extreme pressure and heat. Heat range is perhaps the most important characteristic of a spark plug, since it dictates how efficient and reliable the spark plug will be. Finally, the ability to diagnose the spark plugs is quite possibly the best way to quickly determine the condition of the engine.

Heat Range

  • Spark plugs are measured according to their heat range. Heat range refers to a spark plug's ability to conduct heat away from the tip of the plug. A plug's heat range must balance the ability to avoid pre-ignition by burning too hot with the risk of not producing enough heat to avoid corrosive deposits that can lead to misfiring. A plug's heat range can be identified by first noting the number stamped into the side of the spark plug, then by consulting the spark plug's manufacturer to find out which heat range that number indicates. When replacing the spark plugs, the heat range will be noted on the box. Another way to check the heat rage of plugs that are already in use is to remove the spark plugs and note the condition of the tip of each plug. If the tip is either a clean white color or appears blistered, the heat range is not correct. Always refer to the engine's specification's manual to identify the correct heat range for the particular Chevy engine.

Spark Plug Diagnosis

  • One of the easiest and most effective ways to determine the condition of an engine is to note the condition of the tip of the engine's spark plugs. If the tip is a light tan to grayish color, the engine is operating normally. If the tip is covered with a wet, oily coating, there is an oil control problem. If the plugs have a glossy, black color, the plugs probably just need to be replaced. The glossy black color typically results from hard, fast acceleration, where the normal deposits that have gradually accumulated have melted onto the insulator. If the tip of the plug is covered in black, sooty deposits, the air/fuel mixture might too rich, the choke could be stuck, the air cleaner may be dirty or the engine could have low compression. If the tip of the plug is broken, the engine is detonating, a condition sometimes referred to as "spark knock," as detonation produces an audible knocking sound, particularly upon acceleration.


  • Chilton's Fuel Economy & Tune-Up Tips; Chilton Book Company; 1980
  • Motor's Auto Repair Manual; Ralph Ritchen; 1968
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