Why is spark plug heat range important?

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Spark plug heat range is about how quickly the plug sheds heat from the tip into the cylinder head. The goal is to keep the electrode tip at a temperature where it stays clean of fuel and oil deposits but isn’t so hot that it causes overheating or pre-ignition. If the plug is too hot for the engine, tip overheating can occur and damage the spark plug and combustion chamber. If the plug is too cold, the tip may not reach the self-cleaning temperature, allowing carbon fouling and deposits to build up, which can cause misfires. So the main importance of heat range is to provide adequate heat transfer away from the tip to prevent fouling or overheating across the engine’s operating range. The spark voltage and starting performance are influenced by other factors like ignition system, plug gap, and engine condition, not primarily by the heat range.