Best Spark Plugs: Keep Your Engine Purring With These Top Picks
Keep your vehicle’s engine going strong with these top spark plugs
The Review Team
How We Decided
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PUBLISHED ON April 17, 2019
Don’t let the small size fool you—spark plugs emit an electrical spark across a tiny gap to ignite the combustion required to start your car. By setting your motor’s pistons in motion, your ride can roar to life, stay running, and deliver a smooth burn of the compressed air-fuel mixture. Is your engine due for a spark plug replacement? Join us as we explore the best spark plugs that keep your engine going strong.
- Best OverallNGK (6619) LFR6AIX-11 Iridium IX Spark PlugSummarySummary
The best spark plugs for performance, power, efficiency, and reliability.ProsPros
A good design that is unlikely to misfire or malfunction, superb performance/efficiency, and long lifespan.ConsCons
On the pricey side for a spark plug replacement.
- Best ValueDenso (4504) PK20TT Platinum TT Spark PlugSummarySummary
An affordable platinum spark plug that delivers great durability and performance for your dollar.ProsPros
Excellent price, durable, double platinum tip for enhanced performance.ConsCons
The gap is occasionally set incorrectly, performance isn’t on par with iridium spark plugs.
- Honorable MentionBosch 4417 Platinum+4 FGR7DQP Spark PlugSummarySummary
These exceptional all-around spark plugs offer impressive performance, efficiency, and user-friendliness.ProsPros
Fantastic performance and efficiency, easy to install, gapping not required.ConsCons
Slightly less performance than iridium plugs, pricier than other platinum plugs.
Why Trust Us
All of our reviews are based on market research, expert input, and practical experience with each product we include. This way, we offer genuine, accurate guides to help you find the best picks.
Benefits of Spark Plugs
- 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.
- Improve acceleration and engine response. If you notice that your ride isn’t as peppy as it usually is when you step on the gas pedal, you may need to replace your spark plugs. Healthy spark plugs maximize the combustion process in your engine, giving you smooth, responsive acceleration.
- Smoother engine idle. Fully functioning spark plugs provide sufficient ignition to spur the combustion process in your motor. When spark plugs become faulty, they cause your engine to run rougher than usual, which results in symptoms such as a rough idle. Replacing tired plugs with a set of new plugs will smooth out your idle.
- 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.
- Enhanced reliability. If you’re experiencing difficulties starting your car, truck, or SUV, your spark plugs may need to be replaced. Spark plugs are a crucial electrical component necessary to start your vehicle, so inspect your plugs if you’re having trouble getting your ride running.
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.
Founded in 1916, ACDelco is a Grand Blanc, Michigan-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 4417 FGR7DQP 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-$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.
- Over $9: 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 different 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 does 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 Plug Reviews & Recommendations 2019
Best Overall: NGK 6619 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.
We were hard-pressed to come up with any cons for these spark plugs, but if we had to ding it for something, it would be its rather expensive price per spark plug. This higher price may seem like a big ask for more frugal motorists, but the exquisite quality and peerless performance that the NGK 6619 spark plugs deliver make them well worth their cost.
Best Value: Denso 4504 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 then Denso 4504 PK20TT Platinum Spark Plugs. These value-priced platinum plugs pack a whole 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.
There are a few faults that we found with these double-platinum spark plugs. Occasionally, the gap was incorrectly set on some of the plugs. This is why it’s critical that you inspect the gap and adjust it accordingly. In addition, these double-platinum plugs cannot match the quality, performance, and longevity that iridium spark plugs boast. Nonetheless, we believe that Denso 4504 PK20TT Platinum Spark Plugs are some of the best affordable spark plugs for your car, truck, or SUV.
Honorable Mention: Bosch 4417 FGR7DQP Platinum Spark Plugs
Considering that they’re constructed from a technically inferior material compared to iridium, the Bosch 4417 FGR7DQP Platinum Spark Plugs give iridium options a run for their money. The key to excellent performance lies in their innovative design.
Traditional spark plugs feature a single electrode and cap design, but the Bosch 4417 plugs utilize four yttrium-enhanced electrodes. This advanced design gives these spark plugs outstanding performance and efficiency without having to rely on a more expensive material like iridium. Novice and veteran mechanics alike will appreciate how easy these spark plugs are to install in their vehicles. It’s also a huge plus that these plugs never need to be gapped, making them extremely service-friendly.
One minor drawback worth mentioning is that these spark plugs will not provide quite as much power as iridium options so hardcore auto enthusiasts may want to look elsewhere for their performance fix. Additionally, these platinum spark plugs are slightly pricier than their platinum peers. Regardless, Bosch 4417 FGR7DQP Platinum Spark Plugs strike a good compromise between value and superb overall performance.
- 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 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: Should I use hot or cold spark plugs?
A: 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: How frequently should I change my spark plugs?
A: 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: What are the symptoms of a faulty spark plug?
A: 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: Can I clean my spark plugs?
A: Yes, you can clean your spark plugs, but it’s generally not recommended. When you clean a spark plug using a wire brush or sturdy knife to scrape off the deposits, it can dull it and drastically lower its efficiency. If you insist on cleaning your spark plugs, use a spray-on plug cleaner specifically engineered for this vital component.
Q: Do unopened spark plugs have a shelf life?
A: 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.
Our first place pick for the best spark plugs on the market is the NGK 6619 Iridium IX. These iridium plugs will deliver unbeatable engine performance, fuel efficiency, longevity, and protection from misfires and malfunctions.
If you’re looking for value-priced plugs offering some serious performance, the Denso 4504 PK20TT Platinum Spark Plugs will do nicely.