Gasoline-powered engines come in different shapes and sizes, but they all require three essential elements: air, fuel and spark. The spark makes its way through a distributor, which sends an electrical current along an insulated wire to the individual spark plugs, timed to coincide with an injection of fuel to produce the combustion stroke. Changing spark plugs is normal over the course of any vehicle’s life, and when it’s time, you’ll find you have options. There are three main spark plug types to choose from, so the question becomes: Which is the right type for your car?
The metal center of spark plugs is exposed only on the ends. One end connects to the wire, bringing the spark. The other end holds two electrodes that, once the plug is threaded into the block, poke into the combustion chamber. The middle portion of the plug is encased in porcelain to keep the metallic core insulated from the rest of the block. A precise gap at the end forces the electricity to jump from one electrode to the other, causing a spark that ignites the air–fuel mixture. It’s important that the metal core is highly conductive, heat resistant and hard enough to keep its shape under the stress of the combustion process.
Due to its high conductivity and resilience in the face of heat, copper cores are the oldest and most commonly installed spark plugs. Additionally, manufacturers love it because it’s the cheapest of the three to produce. The Achilles heel of copper, however, is that it’s a relatively soft metal and doesn’t hold up as well under the pressures of time or keep its sharpness as long as the other metals.
Platinum plugs are still copper at their core, but they are platinum plated on the ends to provide extra strength and increase lifespan. As a metal, platinum is stronger than copper, with double plated platinum being — you guessed it — even stronger than that. Unfortunately, it isn’t quite as conductive, which makes it less efficient in the short term. In the long run, though, its lifespan will outlast copper plugs every time. Many people consider the copper vs. platinum contest a draw, as platinum is more expensive upfront.
The last type of metal used is iridium. Like platinum, it’s used on the end to fortify the electrodes for longer life. These are the most expensive plugs available, but they’re not technically higher performing, as they are also slightly less conductive than copper. Still, they last longer than the others and have the highest temperature tolerance of the three. Certain cars are designed such that proper performance and fuel economy actually demands them.
When making the choice to replace old plugs, first consult your owner’s manual. If a specific plug is recommended, stick with that. Otherwise, if you wish to upgrade to iridium, make sure the plug you’re replacing is of similar design, or you might actually do yourself a disservice. Be especially careful if you’ve made aftermarket modifications to your engine. These might require a specific kind of plug to ensure performance. Most importantly, always read your literature first.
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Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter. In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.