ASE G1 Test Prep: Spark Plug Tips

ASE G1 Test Prep: Spark Plug Tips

Take a look at the three most common styles of spark plugs. This video is sponsored by Autolite.


In the mid-’80s, auto manufacturers were scrambling to meet the constantly tightening emissions regulations, which largely meant improving combustion efficiency. Science and engineering stepped in, and one of the biggest areas of research was in the improvement of spark-plug efficiency and performance.

The traditional copper spark plug, as it’s known, simply wasn’t able to provide the necessary performance, and precious metals were the answer, specifically platinum and iridium. The advantage to these is that they have a higher melting point. Nickel alloy, which is the standard material in the center electrode of a copper plug, has a melting point of 2,651 degrees Fahrenheit. Platinum has a melting point of 3,215 degrees Fahrenheit, and iridium, 4,435 degrees Fahrenheit.

The higher melting points of iridium and platinum allowed these spark plugs to be designed and manufactured with smaller-diameter center electrodes. Because the smaller diameter of the center electrode requires lower voltage to start the spark, and because the finer point allows the electrode to absorb heat quicker, the result was spark plugs that not only lasted longer, but provided improved acceleration, drivability and fuel economy.

Let’s take a look at the three most common styles of plugs. The traditional copper spark plug has a copper core, with the center and ground electrodes made of a nickel alloy. Nickel alloy is softer than platinum and iridium, and therefore, it wears out quicker. They require a higher voltage to fire, and have a comparatively short service life, sometimes as low as 10,000 to 20,000 miles.

Platinum spark plugs are known for their long service life due to their heat- and wear-resistant properties. They run hotter than copper plugs, which helps prevent fouling and reduce deposits. They’re expensive, but when you compare the lifespan, it evens out the odds.

Iridium is one of the world’s hardest metals, and it’s very resistant to spark erosion. They require less voltage to fire, improving combustion efficiency. They also have an extended service interval and can last longer than a platinum plug.

Double platinum and double iridium spark plugs feature not only a precious-metal center electrode, but also an additional precious-metal tip on the ground electrode. They offer the maximum in ignition efficiency and sustained spark performance.

The most important thing to remember when installing platinum and iridium plugs is to use extra caution if you need to adjust the spark-plug gap. It’s recommended to use a wire style of spark-plug gauge and use it gently so you don’t damage the precious-metal electrodes.

Even though platinum and iridium have their clear advantages, different spark plugs are designed to work in different engines, and what’s designed for one may not work well for another. There’s a lot of science behind it, and the best practice is to always use a high-quality spark plug that’s recommended specifically for the application. Thanks for watching.

This video is sponsored by Autolite.

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