Best Spark Plugs: Keep Your Engine Purring With These Top Picks
You replace your spark plugs fairly often, so it's important to know which ones are superior.
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BY Zach Faulds / LAST UPDATED ON September 21, 2021
Every morning when you turn over your ignition, you are most likely not thinking about what is happening under the hood—it takes several functioning parts acting in conjunction with each other to get your vehicle’s motor running. Nonetheless, it is a small yet mighty device that starts to put everything into motion.
The spark plug is a powerful piece that delivers the electric current igniting the gasoline-powered internal combustion engine. To get your car’s motor roaring and to keep it running smoothly will require well-fitting spark plugs. Find out which spark plugs are the very best to choose when it comes time to replace them.
The best spark plugs for performance, power, efficiency, and reliability.
- A good design that is unlikely to misfire or malfunction
- Superb performance and efficiency
- Long lifespan
- On the pricey side for a spark plug replacement
An affordable platinum spark plug that delivers great durability and performance for your dollar.
- Excellent price
- Durable, double platinum tip for enhanced performance
- Gap is occasionally set incorrectly
- Performance isn’t on par with iridium spark plugs
These plugs boost cold starts, enhance fuel ignition, and foster optimum performance, reliability, and heat transfer.
- Long lifespan
- May increase gas mileage and boost performance in certain vehicles
- Factory set gap may not be correct
- May not fit all vehicles listed in the specs
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Our reviews are driven by a combination of hands-on testing, expert input, “wisdom of the crowd” assessments from actual buyers, and our own expertise. We always aim to offer genuine, accurate guides to help you find the best picks.
Benefits of Spark Plugs
- Improve performance. Spark plugs made of the chemical element iridium take less voltage to fire, providing several benefits. Iridium spark plugs allow for better combustion, lower emissions, improved fuel economy, and more horsepower.
- Increase fuel efficiency. If your engine is powered by worn-out spark plugs, it will not run as efficiently as intended. When you replace these faulty plugs with a set of fresh plugs, your engine will run smoothly and require less effort to keep the combustion process going. This will translate into increased fuel efficiency over the long run.
- Decrease exhaust emission. By changing your vehicle’s spark plugs, you decrease the possibility of misfires that may occur. When a misfire happens, it increases your car’s exhaust emission. For car owners to reap the benefits, they should pay attention to the warning signs of possible spark plug troubles. Every time you replace new plugs before major issues arise, it can maximize fuel economy and save you money.
- Improve acceleration and engine response. If your vehicle seems sluggish and that you need to increase the pressure on the gas pedal, this is a strong sign that it is time to replace your spark plugs. When spark plugs are in good-shape or healthy, they maximize the combustion process in your engine, giving you a smooth and responsive acceleration.
- Smoother engine idle. When your spark plugs are functioning as they should, they provide adequate ignition to advance the combustion process in your vehicle’s motor. If the spark plugs are faulty, they will cause your engine to deliver a rougher than usual ride or idle. Replace older plugs with a set of new ones, and you may notice a difference in the smoothness of your car’s idle.
- Increase fuel economy. Each time a spark plug misfires, it can reduce your vehicle’s fuel efficiency by as much as a whopping 30 percent.
- Reduce the risk of damage to your engine and other components. Faulty spark plugs can cause misfires, poor fuel economy, lackluster acceleration, and other issues with your ignition system. Left unaddressed, malfunctioning plugs can also cause damage to other components such as your catalytic converter, so it’s vital that you immediately replace bad plugs.
Types of Spark Plugs
Copper core spark plugs are the most basic and affordable type of spark plug that you can buy. These used to be the most common plug type on the market, but have recently been replaced by platinum and iridium spark plugs due to their superior performance, efficiency, and lifespan. While many modern engines simply cannot run copper spark plugs, there are a number of older engines that run better using copper plugs.
Platinum plugs deliver enhanced performance and fuel efficiency compared to copper plugs, but for a considerably cheaper price than iridium spark plugs. Much like iridium plugs, platinum spark plugs operate at a lower temperature than copper spark plugs. They can also last up to twice as long as basic copper plugs.
Double-platinum spark plugs provide even more performance, efficiency, and longevity than single-plated platinum plugs. What’s more, double-platinum plugs are still typically cheaper than iridium spark plugs. For an affordable upgrade from single platinum, just look for spark plugs that use platinum in both the electrode and cap.
The best spark plugs on the market boast an iridium construction. Iridium spark plugs give you even better gas mileage, performance, reliability, and longevity than double-platinum plugs. Due to the advanced material and innovative technology integrated into iridium spark plugs, these plugs are priced higher than copper and platinum options. Iridium spark plugs are perfect to use on high-performance engines.
Double-iridium spark plugs are very much like the double-platinum ones. Double-iridium spark plugs have two discs made of rare metal to increase performance and durability. The design of these spark plugs is to deliver firepower essential for all kinds of driving conditions, including extreme heat or continual high-speeds. Double-iridium can provide up to four times the average life of service than a standard copper spark plug.
Founded in 1916, ACDelco is a Grand Blanc, Mich.-based automotive parts brand owned by General Motors. Offering everything from air conditioning components to batteries, ACDelco is perhaps best known for its line of spark plugs. One of its top products is the ACDelco 41-993 Professional Iridium Spark Plug.
Established in 1886, Robert Bosch GmbH, or simply Bosch, is a massive multinational engineering and electronics company with its headquarters near Stuttgart, Germany. Bosch manufactures a vast diversity of goods, from home appliances to auto parts. One of its best-selling products is the Bosch 6702 Platinum Spark Plug.
Operating from Nagoya, Japan, NGK Spark Plug Co., Ltd. is a public company tracing its roots back to 1936. NGK is best known for its range of spark plugs, though it also manufactures fine ceramics, cutting tools, and more. One of this brand’s popular products is its 6619 Iridium IX Spark Plug.
Spark Plug Pricing
- Under $3: There are several spark plugs available in this value-priced range. Buyers must do their homework before purchasing cheaper spark plugs due to the vastly varying degree of quality.
- $3 to $9: The majority of spark plugs fall into this pricing segment. Most shoppers choose a spark plug priced in this range because they tend to offer an ideal blend of efficiency, longevity, performance, and value.
- $10 and up: Spark plugs priced in this range tend to feature a durable construction using premium materials, advanced electrode designs, and unparalleled performance, efficiency, and longevity.
When you’re shopping for spark plugs, it’s important to consider which material best suits your needs. Copper is ideal for older model vehicles that feature a low-voltage distributor-based ignition. Platinum and iridium are best suited for modern engines without distributors. Platinum delivers a great mix of economy, performance, and longevity. Iridium offers an even better mix but at a higher cost. In the end, always use the plug specified by your vehicle’s manufacturer.
One important way that spark plugs are specified is by the size of the thread or nut. In the United States, typical thread and nut sizes are as follows: 10 millimeters (nut: 16 millimeters), 12 millimeters (nut: 14 millimeters, 16 millimeters, or 17.5 millimeters), 14 millimeters (nut: 16 millimeters or 20.63 millimeters), and 18 millimeters (nut: 20.63 millimeters).
A spark plug is specified as “hot” if it’s a better heat insulator, and it’s classified as “cold” if it can conduct more heat out of the tip and lower its temperature. Generally, manufacturers denote the heat range of a spark plug with a number, with some brands using ascending numbers for hotter plugs and others doing the opposite for colder spark plugs.
Spark plugs are usually engineered to have a spark gap which can be adjusted using a spark plug gapper tool. A single plug may be designed for several engines, necessitating a different gap for each. Spark plugs for cars typically gap between 0.6 and 1.8 millimeters (0.024 and 0.071 inches). Use a gap gauge to measure the plug’s gap to ensure that it’s within the specified range.
- User-Friendliness. Some spark plugs come “pre-gapped” right out of the box and do not require adjustment. These pre-gapped spark plugs are convenient and ideal for consumers looking for a plug-and-play style plug that doesn’t require fussing with a gap gauge and tool during installation. If you have some experience turning a wrench, this may not be a huge deal though.
Best Spark Plugs Reviews & Recommendations 2021
- Have your vehicle information handy when shopping for new plugs to ensure you purchase the right spark plugs for your ride. Your owner’s manual or vehicle registration card should have the following information: model year, make, model, engine displacement, carburetor or fuel injection type, and cylinder count.
- It’s a wise idea to replace your spark plug wires when you change your plugs. Faulty spark plugs can damage the wires, so swapping out both components at the same time will ensure that your engine receives the best ignition parts possible.
- As tempting as it is, don’t always purchase the least expensive option for spark plugs. The best-quality spark plugs are usually more expensive because they guarantee optimal fuel economy, engine performance, longevity, and reliability.
- Inspect your plugs to determine their condition. If the plugs look fine except for a red coating, this could be residual additives from poor-quality gas. Clean them off with a clean cloth and reinstall them. If the plug has black or heavy ash deposits around or on top of its center electrode, this means it must be replaced.
- Before you remove your old plugs, clean the cylinder head around your plugs with a compressed air can or gun. This will blow away any dirt or deposits that may have collected on this area. This is important because dirt can enter the cylinder bore and score the wall and wear the rings.
- Inspect the new spark plugs for any damage. Ensure the side electrode aligns with the center electrode and is straight. If any adjustment is required, use needle nose pliers to gently reposition it.
- With the plug positioned downwards, spray the cavity around the center electrode with carburetor cleaner. This is an effective method to remove any porcelain dust or debris left over from the manufacturing process that can cause misfires.
- Use an anti-seize compound to coat the spark plug thread. This will make it easier to remove the plug in the future without galling the threads in the cylinder head. If any of the anti-seize compound happens to get on the electrodes, wipe it off with a clean rag moistened with carburetor cleaner.
- Use a dielectric compound to coat the secondary wire connection and the insulator where the boot sits. Dielectric compound prevents corrosion and prevents the boots from sticking to the insulator, which can cause the wires to break during future maintenance.
- Never use air tools to remove or install spark plugs in your vehicle. Always thread each spark plug by hand, and then use a proper socket and wrench to tighten the plugs according to factory specifications.
Q: How can you tell when spark plugs are operating at optimum temperature?
If you are wondering how to tell whether your spark plugs are operating well before problems arise, look at their color. Usually, when the spark plug is a light tan or gray color, that should tell you that it is running at optimum temperature. In other words, your vehicle’s engine is in good condition.
Q: How long do spark plugs last?
The life-span of spark plugs varies by both manufacturer and vehicle. Yet, the spark plugs in most vehicles sold on the market today should last for 100,000 or more miles. To ensure you do not go past your spark plugs interval, research the type of spark plugs to learn whether they are suitable for your vehicle. Keep in mind that the spark plugs in most performance and luxury models tend to have shorter intervals.
Q: How frequently should I change my spark plugs?
This depends on the quality of spark plugs you have in your car. Top-quality spark plugs will last longer than lower-quality plugs. Most mechanics recommend you change your copper core spark plugs every 30,000 miles or every 50,000 miles for iridium core spark plugs. This interval may be shorter if your engine isn’t in top condition, so it’s vital to inspect your spark plugs for premature wear and change them accordingly.
Q: Will a faulty spark plug turn on the check engine light?
When your vehicle has a faulty spark plug, it can cause the check engine light to illuminate, signaling an issue. In some instances, the check engine light may even be flashing instead of a solid light. When the warning light appears, it is essential that you or a professional mechanic look into the cause.
Q: What are the symptoms of a faulty spark plug?
You may notice the following symptoms if your spark plugs need to be replaced: hesitation or backfiring during acceleration, decreased acceleration, rough idle, spark plug wires charred on the end that goes onto the plugs, a significant drop in fuel economy, and difficulties starting your engine. If your ride doesn’t run as well as it usually does, and you suspect it’s attributed to bad spark plugs, inspect the plugs yourself or have a mechanic do it.
Q: What happens if you do not replace your spark plugs?
To avoid damaging your engine and experiencing driving issues, your vehicle’s spark plugs must be replaced. Over time, spark plugs will start deteriorating, and they will not spark as they are supposed to, thus, not igniting the air/fuel mixture, leaving the combustion process unfinished. Your vehicle will eventually experience a loss of engine power, and in the worst-case scenario, the engine will stop running altogether.
Q: Should I use hot or cold spark plugs?
In typical driving circumstances, you should use the spark plugs specified by your vehicle’s manufacturer. A hot plug may be a good option if your spark plugs are fouled from carbon deposits, your engine has a rich air-fuel ratio or burns oil, or if you do a lot of local low-speed driving. If your engine is pinging, has a lean air-fuel ratio, or if you do a lot of high-speed driving, consider a cold plug.
Q: Do unopened spark plugs have a shelf life?
As long as unopened spark plugs are properly stored in a dry, cool environment, then they should last an indefinite amount of time. The lifespan of spark plugs is impacted only when they are exposed to corrosive environmental factors such as moisture or if they’re dropped frequently.
For a high-quality spark plug, consider the NGK 6619 Iridium IX Spark Plugs, featuring excellent performance, power, efficiency, and reliability. Or, choose the Denso 4504 PK20TT Platinum Spark Plugs, an affordable platinum spark plug that delivers excellent durability and performance.