What do the spark plug numbers indicate about the plug's heat range?

The number associated with a spark plug indicates its heat range, which is crucial for engine performance. A lower number signifies a hotter plug, meaning it can reach higher temperatures during operation. This heat is necessary for burning off any carbon deposits and ensuring proper combustion. A hotter spark plug can help in high-performance engines where higher temperatures are needed for efficient fuel burning.

In contrast, a higher number indicates a cooler spark plug designed to operate at lower temperatures, which reduces the risk of pre-ignition and protects the engine in situations where it may run too hot. Thus, understanding the numerical scale linked to spark plug heat ranges allows for better selection for various engine types and conditions, ensuring optimal performance and longevity of the component.