Copper spark plugs: debunking the myth

I read a lot of online auto blogs and continually see folklore “wisdom” that copper spark plugs are a better choice than either platinum or iridium. Rubbish! The myth is based on the fact that copper is a better electrical conductor than the more expensive precious metals. That’s true, as far as it goes. But there’s far more to creating a powerful spark than just the conductivity of the electrode material.


The myth ignores the fact that an ignition spark always jumps from (and toward) the sharpest parts of the center and side electrodes. Sure, a copper spark plug has sharp electrodes right out of the box. But copper can’t maintain sharp edges very long. The heat of the spark itself and high combustion temperatures quickly wear down the edges of both the center and side electrodes. That’s because copper has the lowest melting point of all the currently available spark plug materials (copper melts at 1,983 degrees F, yttrium at 2,779 degrees, platinum at 3,222 degrees and iridium at 4,229 degrees). Copper plugs actually experience rapid edge wear and increased spark plug gap in as little as 10,000 miles. And that results in a far less powerful (and less effective) spark that can misfire, lower your gas mileage and damage ignition wires and the coil.


Premium spark plugs, on the other hand, hold their sharp edge and maintain the proper gap for up to 100,000 miles. With the highest melting point of all the precious metals, iridium-tipped spark plugs are now considered the best choice for quick starts, solid acceleration and overall long-term performance. So ignore the myth of the copper spark plug and spend a few extra bucks on a premium spark plug.
Iridium Spark PlugTraditional Copper Spark Plug
Iridium and platinum spark plugs are available from a variety of manufacturers.

To learn how to install spark plugs, visit:

— Rick Muscoplat, Automotive Editor