What do the markings on a spark plug represent?
2 Answers
Each brand of spark plug has different model numbers, which are generally printed on the spark plug casing. These markings represent the material, size, heat range, resistance, and gap of the spark plug. Here is a partial introduction to spark plugs: 1. The size of spark plugs is standardized worldwide and can be used universally in any vehicle. However, due to differences in gasoline engine types, spark plugs are divided into two basic types: cold type and hot type. The terms "cold" and "hot" are relative and reflect the thermal performance characteristics of the spark plug. A spark plug must maintain an appropriate temperature to function properly and avoid carbon buildup for optimal performance. 2. The temperature varies in different engines, and designers address this by adjusting the length of the insulator skirt. Some spark plugs have shorter skirts, which have a smaller heat-absorbing area and dissipate heat quickly, resulting in lower skirt temperatures. These are called cold-type spark plugs and are suitable for high-speed, high-compression-ratio, high-power engines. Others have longer, slender skirts with a larger heat-absorbing area and slower heat dissipation, leading to higher skirt temperatures. These are called hot-type spark plugs and are suitable for medium-to-low-speed, low-compression-ratio, low-power engines.
I've been tinkering with cars for over a decade, and those markings on spark plugs aren't just random prints—they indicate model specifications to help you pick the right part without mistakes. Take the NGK spark plugs I use, for example: the first few characters represent the heat range. A higher number means the spark plug runs hotter, suitable for regular city driving, while a lower value is better for high-speed engines. I once tried using the wrong heat range, and the engine shook terribly while guzzling fuel. The middle letters indicate the gap size—the distance the spark jumps. Too large, and it won't ignite; too small, and it risks burning out—always follow the vehicle manual. The trailing letters often denote materials like platinum, affecting lifespan and performance. I've switched to iridium ones, which feel impressively durable. And the brand name is clearly marked—buying fakes would be a huge waste. Essentially, these markings exist to simplify matching and avoid confusion. Once you understand them, changing plugs becomes hassle-free and cost-effective. I recommend checking them every 20,000–30,000 km to ensure they haven't degraded.
