Your guide to a better future
Spark plugs are a mission-critical part of a gasoline engine's ignition system. Without them, there's nothing to ignite the air-fuel mixture in each cylinder.
Craig brings 15 years of automotive journalism experience to the Cars team. A lifelong resident of Michigan, he's as happy with a wrench or welding gun in hand as he is in front of the camera or behind a keyboard. When not hosting videos or cranking out features and reviews, he's probably out in the garage working on one of his project cars. To date, he's fully restored a 1936 Ford V8 sedan and is currently resurrecting another flathead-powered relic, a '51 Ford Crestliner. Craig is a proud member of the Automotive Press Association (APA) and the Midwest Automotive Media Association (MAMA).
Are you someone who drives a gas-powered car? Has there ever been a time when you've thought about your car's ignition system? If your answer is no, don't worry -- you are definitely not alone. Spark plugs, coil packs and high-tension leads are your vehicle's unsung under-the-hood heroes as they play one of the most important roles in the four-stroke combustion cycle. These parts join forces to ignite the delicately balanced mixture of air and fuel in each cylinder, which is ultimately what sends you zooming on down the road.
The business end of an ignition system is the humble spark plug. On the surface, these cylindrical, threaded components seem simple, but there's an incredible amount of engineering that goes into each one. Beyond that, there's a dizzying array of spark plugs on the market, with specific designs for everything from lawnmowers to race cars. There are different electrode materials and plug lengths, heat ranges vary based on application and some spark plugs are intended strictly for turbocharged or supercharged engines.
But what's the best kind of spark plug to buy if it's time to replace them in your ride? Well, this is actually an easy question to answer. Hans Lipp, director of ignition application engineering at DRiV Motorparts, a division of Tenneco, summed it up best, "[Make sure] the spark plug that you put into your engine is actually recommended for this specific engine," especially the heat range. If you don't do this, he added, "very, very bad things can happen." Manufacturers provide specific information about the plugs you should use, part numbers that can easily be cross-referenced to find compatible plugs from different manufacturers if you don't feel like purchasing an OEM spark plug.
Demystifying things, this guide highlights some of the best spark plugs on the market today and delves into related terminology. Our recommendations in various categories are based not only on expert knowledge but also real-world customer reviews.
If you drive a low-performance vehicle or have a classic car, you can probably get away with running copper-core spark plugs. These should also work well in small engines, like ones on lawnmowers, chainsaws or string trimmers. No, a copper spark plug doesn't last as long as newer designs and they may not perform as well, but in certain cars and trucks they're all that's needed, plus they're super affordable; these Champions go for just about five bucks apiece. With a corrosion-resistant body and a copper core for reliable performance, they should provide years of trouble-free service. Icing on the cake, these copper plugs are also highly rated, having received 4.8 stars out of five after more than 3,750 customer reviews.
If you've determined that a copper plug will work in your particular application and you don't want to spend any more hard-earned money than necessary, consider these super-affordable Autolites. Sold in four-packs, these plugs sticker for about $10, or roughly just $2.50 apiece. Sure, these no-frills copper core spark plugs are a bargain, but don't let that low, low price fool you: The Autolite is still a solid product, one that carries an impressive 4.7-star rating.
For greater performance than copper-core spark plugs provide, consider stepping up to platinum. Plugs incorporating this precious metal should last longer and deliver more spark energy to each cylinder. The Denso Platinum TT spark plug should also improve fuel economy, enhance acceleration and provide quicker engine starts. This design features a platinum-tipped center electrode, which fires against a titanium-enhanced ground strap. The purified alumina powder insulator is designed to withstand extreme stress and deliver excellent dielectric strength and thermal conductivity. These Denso spark plugs are a great value, and they're highly regarded, having earned a 4.6-star rating after nearly 1,000 customer reviews.
Double-platinum spark plugs are another step up the ladder. They feature platinum on both the center and ground electrodes, a more efficient design than what's found on a standard platinum plug. This double platinum spark plug configuration should provide many of the same benefits -- like greater performance, enhanced engine smoothness and better efficiency -- but they should last even longer than regular platinum spark plugs. Champion's heat-active alloy is expected to help these plugs maintain a stable operating temperature under all driving conditions for strong performance across the board. With a rating of 4.5 out of 5 stars, they clearly deliver on their promises. And at less than 5 bucks a pop, there's no reason not to consider a set when it's time to change spark plugs.
Movin' right along, iridium-tipped spark plugs should provide even greater performance and longevity than double-platinum plugs, since this silvery transition metal has a high melting point. The NGK Iridium IX spark plug is designed for performance enthusiasts, claiming to deliver enhanced throttle response and superior resistance to fouling thanks to its long insulator nose. Keeping combustion gasses where they belong (that is, in the cylinders) is a triple-layer gasket. The anti-corrosion trivalent metal plating on the body and threads of these iridium plugs reduces the likelihood of them getting stuck in a vehicle's cylinder head, even after many years of hard service. As for customer ratings, this iridium spark plug has earned 4.7 stars out of five after nearly 1,300 reviews.
In the world of gasoline-engine ignition, NGK's Ruthenium HX spark plugs sound like the cat's pajamas. Designed to last for the long haul in today's fuel-efficient, high-output engines, these plugs promise maximum durability and service life in turbo and direct-injected applications. Thanks to their high ignitability, these plugs promote a more complete fuel burn for quicker throttle response, smoother idling and better cold starts. With their superior oxidation resistance and the ruthenium alloy's greater durability, these could be the last spark plugs you ever need to buy, which is helpful in engines where the plugs are difficult to access, such as a transversely mounted V6.
It's great if you've decided to replace the spark plugs in your vehicle, but you can't do it without the appropriate tools. Since most spark plugs are buried deep inside the cylinder head, you can't just unscrew them with a wrench, you need a special socket and a ratchet, likely with an extension. Ensuring you have exactly what you need is this five-piece spark-plug socket set from Ares. In addition to an organizer, it includes a 14-mm and an 18-mm socket, as well as 5/8, 3/4 and 13/16 on the imperial scale. With these tools you'll have nearly everything you need to remove just about every kind of spark plug out there. And unlike conventional sockets, these feature a small rubber doughnut inside that holds the spark plug in place as you install it. This prevents you from dropping the plug, which could change the gap, resulting in poor engine performance. Aside from being super handy, this set is affordable at about $19.
Before installing any spark plugs, you have to gap them first, or precisely set the distance between the center and ground electrodes, which is measured in millimeters or thousandths of an inch. Automakers specify a certain gap for each vehicle, which is optimized for the application. This CTA Tools ramp-style spark-plug gapper is easy to use and affordable. Plus: It's so small, it fits on a keyring.
Easier to use than a ramp-style gapping tool, feeler gauges give you a precise spark-plug gap every time. If your vehicle manufacturer specifies a gap of 35-thousandths of an inch (0.035), then just fan out a 15-thousandths and a 20-thousandths feeler and you're good to go. If the gap is too wide, just tap the spark plug on a flat surface to close it up so the feelers have some drag. If it's too tight, bend it to open it more. Feeler gauges can also be used in other applications beyond just setting spark-plug gaps.
Spark plugs, deceptively simple, important.
Which spark plug is best for your vehicle? It's important to follow the manufacturer's recommendation or bad things can happen.
From affordable copper-core models to ones fitted with iridium electrodes, there's a dizzying number of different spark plugs on the market today. You can get plenty of use out of a more-affordable set of plugs, especially if you plan on changing them more regularly than the manufacturer recommends. But you can also buy top-of-the-line spark plugs if you never want to think about them or if they're particularly difficult to change, such as on a transversely mounted V6 engine.
When changing out your ride's spark plugs, go slowly, work carefully and, at the risk of sounding like a broken record, follow the vehicle manufacturer's recommendations. Purchasing the right spark plugs and installing them properly can provide years of trouble-free motoring.
Read more: Best Spray Car Wax for 2022