Reviews

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 May 27, 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.

Best Overall
NGK LFR6AIX-11 Iridium IX Spark Plug
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Summary
Summary

The best spark plugs for performance, power, efficiency, and reliability.

Pros
Pros
  • A good design that is unlikely to misfire or malfunction
  • Superb performance and efficiency
  • Long lifespan
Cons
Cons
  • On the pricey side for a spark plug replacement
Best Overall
NGK LFR6AIX-11 Iridium IX Spark Plug
Best Value
Denso PK20TT Platinum TT Spark Plug
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Summary
Summary

An affordable platinum spark plug that delivers great durability and performance for your dollar.

Pros
Pros
  • Excellent price
  • Durable, double platinum tip for enhanced performance
Cons
Cons
  • Gap is occasionally set incorrectly
  • Performance isn’t on par with iridium spark plugs
Best Value
Denso PK20TT Platinum TT Spark Plug
Honorable Mention
Bosch  Copper with Nickel Spark Plug
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Summary
Summary

These plugs boost cold starts, enhance fuel ignition, and foster optimum performance, reliability, and heat transfer.

Pros
Pros
  • Long lifespan 
  • May increase gas mileage and boost performance in certain vehicles
Cons
Cons
  • Factory set gap may not be correct
  • May not fit all vehicles listed in the specs
Honorable Mention
Bosch  Copper with Nickel Spark Plug

Why Trust Us


All of our reviews are based on market research, expert input, or practical experience with most products we include. This way, we offer genuine, accurate guides to help you find the best picks.

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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

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

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

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.

Iridium

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

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.

Top Brands

ACDelco

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

Bosch

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

NGK

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.

Key Features

Material

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.

Size

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). 

Heat Range

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.

Gap Style

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. 

Other Considerations

  • 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

Best Overall
NGK Iridium IX Spark Plugs

NGK 6619 Iridium IX Spark Plugs snagged the top pick in our spark plug comparison because they offered the best mix of high-performance, fuel efficiency, durability, and dependability. Featuring an iridium construction, these high-quality spark plugs provide a longer lifespan than copper and platinum spark plugs.


Its ultra-fine electrode wire promises superior fuel efficiency as well as silky-smooth engine idle and response. You can also expect a healthy boost in power and torque, thanks to the optimal air-fuel mixture that these iridium spark plugs generate. It receives top marks for durability too, with such impressive features as metal plating to resist corrosion and seizing, as well as a long insulator nose to prevent fouling.

Best Value
Denso PK20TT Platinum Spark Plugs

If you’re in the market for solid all-around spark plugs that are easy on your wallet, look no further than Denso 4504 PK20TT Platinum Spark Plugs. These value-priced platinum plugs pack a lot of performance, efficiency, and durability for a downright reasonable price.


Featuring a dual-platinum construction, with a platinum disc and platinum electrode tip, these spark plugs provide a reliable spark to generate smooth, reliable combustion of the air-fuel mixture. This translates to great engine dependability, fuel efficiency, and performance. Another impressive feature is purified alumina powder, which is used as an insulator to increase thermal conductivity for maximum longevity.

Premium Pick
Bosch ZGR6STE2 Copper with Nickel Spark Plug

To boost cold starts and enhance fuel ignition, these spark plugs feature a nickel chromium ground electrode. They have a heavy-duty yttrium enhanced copper core center for optimum performance, reliability, and heat transfer.


These plugs are very durable and have a long lifespan. The nickel-plated shell provides anti-seize and corrosion protection. No gapping is required, and the plug's ribbed insulator prevents flashover. The plugs remedy misfires in certain vehicles, can increase mileage in some vehicles, and may boost performance by a noticeable amount.

Most Durable
Bosch X5DC Copper with Nickel Spark Plug

This OE replacement plug has a long lifespan and is very durable. The iridium firing pin is welded with a 360-degree continuous laser, and the copper core is designed to reduce fouling. The wire is ultra fine, and the nickel-plated shell prevents it from seizing. No gapping is required, and the plug has corrosion protection.


One of the best things about these plugs is that they last a long time, which is important if you have an engine in which the plugs are difficult to access. While you may not notice a change in mileage when you install them, you may see a boost in performance. They are also very reliable, and you don't need a special gap tool for installation.

Honorable Mention
NGK ZFR6F11 V-Power Spark Plug

This spark plug includes a 90 degree V-Power center copper or platinum electrode that provides performance, improved ignitability, increased fuel economy, and lower emissions over your standard spark plug. It is completely corrosion-resistant and has anti-seizing properties. The unique cut in the center of this spark plug helps to direct the spark to the edge of the electrode for a faster, more efficient performance. The corrugated rib design helps prevent flashover, while the pure alumina silicate ceramic insulator provides superior strength and better heat transfer than your average spark plug. This model is highly durable, protected against electrical and chemical wear, and includes a triple seal to prevent leakage.


One downside is that some customers reported the coils of their spark plug to be defective. Ensure to inspect your product upon delivery to double-check that there are no defects or manufacturing issues before installing it in your vehicle.

Honorable Mention
ACDelco 1 Professional RAPIDFIRE Spark Plug

This spark plug is designed for everyday use, and it can be used in most vehicles on the market today. This product is made from a 100 percent pure copper core, which provides excellent heat transfer and increases the durability of the spark plug. A ribless insulator is designed to improve the plug-to-boot seal and prevent leakage. A solid-state suppressor with a two-piece glass and brass seal reduces radio frequency interference and regulates spark energy for a longer electrode life. It also protects against high combustion pressures. The platinum on the center electrode maximizes the performance of this spark plug by enabling superior spark characteristics and reducing the voltage requirements of the vehicle's ignition system.


Keep in mind that these are not iridium spark plugs, and so they will not work in every vehicle. Ensure to construct your owner's manual before purchasing to ensure that they are the correct option for your vehicle's engine.

Honorable Mention
Champion Copper Plus C33-438 Spark Plug

The Champion Copper Plus C33-438 Spark Plug is a versatile option available to purchase in a value four-pack. This product features a nickel alloy center and a ground electrode that provides reliability and durability. The copper included in the center electrode allows for an increase in conductivity and heat control than your average, everyday spark plug. This spark plus makes an excellent choice for all types of automotive engines, particularly older models. In addition to vehicle engines, this spark plug can be used in lawn and garden applications and smaller engines. Make sure to consult your vehicle's owner's manual or instruction manual for your equipment before using these spark plugs as a replacement in your engine.


One downside is that it is not an ideal option for many new vehicles and newer engines. Always make sure to consult your manual or contact your vehicle manufacturer before attempting to install new spark plugs.

Honorable Mention
Motorcraft SP546 Spark Plug

The Motorcraft Spark Plug SP546 is one of the most reliable products on the market. This spark plug includes a two-year warranty covering unlimited mileage, limited labor cost, and no commercial exceptions. This product can be used in vehicles of all types and sizes, ranging from cars to trucks, from both domestic and international manufacturers. A standard copper core helps to maximize performance, reduce corrosion and arc erosion. A multi-rib insulator protects against potential misfires upon starting your vehicle. This spark plug is made from a nickel alloy that is nickel-plated for additional corrosion resistance. It can be used as a reliable replacement spark plug for older model-year vehicles and some newer models. 


Some customers have reported potential problems after extensive use. If you have any issues within two years, reach out to the company regarding a replacement, as the spark plug should be covered under warranty.

Honorable Mention
NGK Laser Platinum PZFR5F-11 Spark Plug

This spark plug is available to purchase in a value four-pack, so you never have to worry about running out in case of an emergency. The platinum design has a longer service life compared to conventional nickel spark plugs. This spark plug provides stable idling, superior anti-fouling, improved fuel efficiency, and lower emissions. It is made from a combination of high-grade pure alumina ceramic and a 98 percent pure copper core, which prevents the spark plug from overheating and provides reliable starts. This product can be used in most engines, but make sure to consult your vehicle's owner's manual or contact your vehicle manufacturer before installing.


The only major downside of the NGK Laser Platinum PZFR5F-11 Spark Plug is its price point. However, since you can purchase four spark plugs in one value package, it is a relatively reasonable price for the quality, performance, and reliability that this spark plug provides.

Honorable Mention
Denso SK20R11 Iridium Spark Plug

The Denso Iridium spark plug does a lot to help the motorist. It’s explicitly designed to improve performance, which is a big demand for any vehicle today. But because it relies on iridium, it also provides a long lifespan to help reduce maintenance requirements and costs.


The iridium helps this plug last far longer than platinum and copper plugs, but that’s no surprise. It’s the tapered electrode that helps this plug meet the demands of performance. The shape of the electrode makes for much easier startups and improvements in acceleration. You may also see some slight improvements in fuel economy as well because of the temperature control.

Honorable Mention
Bosch Double Iridium OE Replacement Spark Plug

It might not be a surprise that Bosch is entering our list again with one of the longest living plugs out there. The double-platinum design helps these plugs last up to four times longer than conventional options. But we should say that Bosch has outdone themselves by ensuring everything will help it live nearly as long as the vehicle.


We’ll start by highlighting the essential details. Again, it uses a double-iridium design to maximize reliability, heat control, and wear resistance. But to aid in performance, an ultra-thin .6 millimeter tip is present. That tiny tip makes for a hotter yet easier ignition to boost performance. It’s got a ribbed insulator that helps to prevent misfires as well. And you can’t look past the nickel-plated shell, which offers total corrosion-resistant and anti-seize properties.

Tips

  • 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.

 FAQs

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.

Final Thoughts

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.