The Best Spark Plugs (2021 Guide)

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A modern vehicle’s engine consists of a plethora of parts, all of which play an important role in its operation. However, none of these are as overlooked yet as pivotal as the humble spark plug.

If you have a car with a petrol-burning internal combustion engine, then spark plugs are a part of it. They provide the electric current that produces a spark igniting the air fuel mixture inside the combustion chamber, thus kickstarting and keeping the engine running.

In order for your vehicle to work within optimal conditions, it’s important to select the right spark plugs and keep them well maintained. Here we’ll point to some of the best choices on the market and later in the article explain everything you need to know about spark plugs, to help you make the right choice for your vehicle.

Spark Plug Comparison Table

Spark PlugsOur VerdictCenter electrode (tip) materialGround electrode materialLifespan (km)Check Price
NGK Iridium IXBest for Most PeopleIridiumNickel60,000eBay
Denso Iridium TTBest Longevity and PerformanceIridiumPlatinum100,000eBay
NGK Laser PlatinumBest for Wasted Spark Distributor Ignition SystemPlatinumPlatinum100,000eBay
Denso Platinum TTBest Budget OptionPlatinumTitanium100,000eBay
Bosch Double Iridium P2PAlso GreatIridiumIridium80,000Amazon

Best for Most People: NGK Iridium IX Spark Plugs

NGK is the world’s largest spark plugs manufacturer and produces some of the finest spark plugs on the market. You can’t go wrong with their products regardless of the spark plug type or purpose you’re looking for. The downside of NGK’s popularity is a market flooded with counterfeits, so double-check before buying.

The NGK Iridium IX spark plug boasts a 98% pure copper core with a high-grade iridium centre electrode tip for increased heat dissipation and improved ignition. The NGK iridium spark plug has an ultra-wide heat range making it a perfect choice for performance engines. It also boasts a long insulator nose to prevent fouling.

Meanwhile, the iridium IX plugs sport a nickel ground electrode with a tapered cut to reduce quenching and increase ignitability. A nickel ground electrode reduces its longevity compared to a dual precious metal plug such as NGK laser iridium (platinum ground electrode).

Our research has shown that NGK iridium’s are some of the most reliable spark plugs on the market and that they’ll easily last even longer than what the manufacturer recommends. This doesn’t mean you shouldn’t replace them when the time comes, though.

Pros:

  • Superb performance
  • Extreme heat range

Cons:

  • Mid to high price overall, but affordable as iridium plugs go
  • A lifespan of 60,000km is mid-tier
  • Beware of counterfeits

Best Longevity and Performance: Denso Iridium TT Spark Plugs

As part of the Toyota Group, you can rely on Denso to deliver quality and reliable parts across all fields. The Iridium TT spark plugs are some of their best spark plugs available.

Denso’s advantage lies in their unique Denso Twin-Tip design for centre and ground electrodes with the smallest tip on the market. With the former measuring 0.4 mm in diameter and the latter measuring 0.7 mm, the Denso Iridium TT plugs require lower voltage to provide a spark. This, in turn, allows them to deliver more complete combustion and provide better engine performance and fuel efficiency in the process.

We have found Denso Iridium TT spark plugs to be an excellent choice for those in need of long-lasting spark plugs with top-notch performance. They’re especially useful to those with particularly hard-to-reach spark plugs as there’s no sense in disassembling half the engine to fit in conventional plugs that’ll only last 20,000 kilometres or so.

Pros:

  • More complete combustion for increased performance
  • Long lifespan of over 100,000km

Cons:

  • High price

Best for Wasted Spark Distributor Ignition Systems: NGK Laser Platinum Spark Plugs

Featuring both the platinum core and ground electrode, the NGK laser platinum spark plugs represent an improvement over their single precious metal counterparts like the NGK Iridium IX or NGK G Power platinum plugs.

Due to its fine wire platinum core and ground electrode with a platinum disc welded to its backside, the NGK Laser Platinum plugs provide a long lifespan and stable ignition throughout it. Meanwhile, their trivalent metal plating provides superior anti-corrosion and anti-seizing properties.

They’re designed alongside OEM’s and can be found in a plethora of different cars out there. With that in mind, there are precious few upgrades to laser platinum (double platinum) spark plugs, and NGK’s own iridium spark plugs are probably one of them.     

Due to their double-platinum structure, they’re best used in vehicles with wasted spark distributor ignition system.

Pros:

  • Long service life of 100,000km
  • Good performance
  • High ignitability

Cons:

  • High price
  • Although top-notch, iridium plugs are still better overall

Best Budget Option: Denso Platinum TT Spark Plugs

Previously reserved for iridium plugs exclusively, Denso’s Twin-Tip technology is now available with their budget platinum option as well.

Thanks to its platinum centre and titanium-enhanced alloy ground electrodes, Denso Platinum TT spark plugs are almost as durable as their iridium counterparts. Measuring 1.1 mm in diameter, the platinum electrode isn’t as narrow as iridium ones and requires higher voltage to run. This limits the platinum TT plug’s performance compared to the best spark plugs on the market, but not by a significant amount.

Also on the downside, we’ve found that they sometimes come with inconsistent gapping (the gap between the electrodes is different even between the spark plugs from the same package). This issue is easily resolved with a gapping tool though.

The Denso TT platinum plugs, however, more than make up for it by being two to three times more affordable than the comparable iridium spark plugs. Also, their purified alumina powder insulator is capable of withstanding the most extreme of conditions while simultaneously delivering excellent thermal conductivity.

Pros:

  • Affordable price
  • Long life of up to 100,000km
  • Good performance

Cons:

  • Performance and longevity not on par with the top-tier choices
  • Inconsistent gapping

Also Great: Bosch Automotive Double Iridium P2P Spark Plug

Bosch Automotive is one of the leading manufacturers of parts and components in the auto industry, and there’s a high chance one of their parts has found a way into your car as well.

Bosch Double Iridium Pin-To-Pin spark plugs boast a similar dual-tip technology as Denso TT plugs but feature a slightly wider 0.6mm fine wire firing pin. Unlike their Denso counterparts, Bosch P2P spark plugs also feature a tapered ground electrode with laser welded iridium tip for improved performance and longevity.

Typically an OE part in newer German cars, Bosch Automotive spark plugs are often hidden inside many modern engines. Being extremely popular, however, means that they’re also one of the most counterfeited car parts around, and knock-offs tend to be of extremely poor quality.

Pros:

  • Long life of over 80,000km
  • Superb performance

Cons:

  • High price
  • Watch out for counterfeits

Spark Plug Buying Guide

Still unsure about which spark plug suits you best? Below we cover everything you need to know about spark plugs.

Spark Plugs 101

The easiest way to describe what the spark plugs do is to say that they do the heavy lifting in the ignition process. A spark plug is an electrical device and part of the vehicle’s ignition system that generates a power spark of electricity which, in turn, ignites the compressed air and fuel mixture in the combustion chamber. The energy produced in the explosion is then used to push the piston and move your car.

Like most car components, spark plugs have evolved, and we now have myriad options to choose from. They can differ in size, shape, operating temperature, and various other factors. However, the most common spark plug classification is by the material from which their central electrode is made.

1. Copper/nickel

The copper/nickel spark plugs have a copper core, but since the material is soft and unsuitable for the high-heat environment of the engine interior, they’re coated with nickel-alloy. They have the largest-diameter electrode of all the spark plug types and thus require the highest voltage to generate a spark.

These are the entry-level spark plugs best suitable for old engines of the pre-high-energy ignition era. However, some modern high-compression and turbocharged engines also work best with copper spark plugs due to their ability to deliver the best spark.

Pros:
  • Inexpensive
  • Provide the best spark for increased performance
Cons:
  • Require higher voltage
  • Shorter lifespan (between 15,000 and 30,000 kilometres)

2. Platinum

Platinum spark plugs are more expensive, more durable, and generate more heat than their copper spark plug counterparts, which reduces carbon buildup. They come in single platinum and double-platinum guises with the former sporting a platinum centre electrode and the latter having a side ground electrode made of platinum as well.

Platinum plugs are typical OEM parts in modern vehicles and the most common option nowadays. Moreover, double platinum plugs are great for wasted spark ignition systems that cause spark plugs to fire twice – both in the compression stroke’s cylinder and in the exhaust stroke’s cylinder.

Pros:
  • Long lifespan (between 60,000 to 100,000 kilometres)
  • Reduced carbon buildup
Cons:
  • Expensive
  • High but not the best performance

3. Irridium

Iridium spark plugs are the most expensive options on the market, but they also last the longest since iridium is six times harder and eight times stronger than platinum. Moreover, iridium has a 700°C higher melting point than platinum, allowing it to operate at an even higher heat. Finally, iridium plugs boast a fine wire centre electrode (iridium tip) designed to conduct electrical energy more efficiently.

Iridium spark plugs are becoming more common with each passing day as more and more automakers have started recommending them.

Pros:
  • Longest life span (between 100,000 and 150,000 kilometres)
  • Require lower voltage
  • More complete combustion
  • High melting point
Cons:
  • Typically the most expensive
  • Performance not as good as that of copper plugs but better than that of platinum ones

4. Silver

Silver spark plugs are the best thermal and electrical conductors among the bunch, which provides the best spark. To that end, they’re often used in high performance engines of both cars and motorcycles. They don’t feature the long lifespan of their platinum and iridium counterparts, however.

An average consumer will typically look for silver plugs if he/she owns an older European performance car or a motorcycle. Professional racecar drivers that are driving pro mod vehicles with 4,000+ horsepower engines and those who drive cars running on alternative, hard to ignite fuels such as alcohol, E85, CNG, LPG, or Nitromethane are also prospective silver plug shoppers.

Pros:
  • Best performance of all spark plug types
  • Good for hard to ignite fuels
Cons:
  • Shorter lifespan (between 50,000 and 80,000 kilometres)
  • Inexpensive but not the cheapest

How to tell when it’s time to replace your spark plugs

Although every spark plug manufacturer will list the expected lifespan of their plugs, there’s no guarantee they’ll actually last that long. That’s why the best course of action is to look for signs that a spark plug is on its last legs.

1. Check engine light is on

The dreaded check engine light is a universal sign that there’s something wrong with your car, and the problem might just be a faulty or failing spark plug. If the OBD2 Scanner returns the code relating to misfires, this means it’s time to replace your spark plugs.

2. The car has trouble starting

There are a few possible culprits if your car is exhibiting difficulties starting, and spark plugs are one of them. Since they provide the most important element of the combustion process – the spark itself – it’s evident how worn out or faulty spark plugs can impact the vehicle’s start.

3. Lower fuel efficiency

Deteriorated spark plugs won’t be able to burn the fuel as effectively as healthy ones, and your fuel economy will suffer for it.

4. Engine misfires

While a misfire can be caused by a number of reasons, including poor quality fuel, more often than not, it’s caused by one or more faulty spark plugs. When a spark plug fails, the cylinder it serves stops working as well.

With one or more cylinders out of commission, the remaining cylinders will have trouble making up for them, and the engine will exhibit a dip in power. Moreover, the air/fuel dollop will continue to enter the dormant cylinder but without being burned. This can potentially lead to catalytic converter damage.

5. Rough engine idle

Although the rough idle symptom can be attributed to a number of potential issues, it might be worthwhile checking on your spark plugs before proceeding with more expensive work.

6. Slow acceleration

If your car’s response time when accelerating is unusually long, the problem can be traced back to worn out spark plugs.

7. Loud engine

Rattling noises and louder engine operation are another one of potential faulty spark plug symptoms. When one of the engine’s cylinders is out of commission, the remaining ones are trying to make up for it, raising the noise levels in the process.

Where in the engine are spark plugs located?

Spark plug location within the engine bay depends on the engine configuration and its type. Spark plugs are typically located on the top or side of the cylinder head. The easiest way to find them is to follow the set of wires under the bonnet, as each of them leads to one of the plugs protected by the plug cover.

Sometimes, however, they can be found under the valve cover or be hidden from view by other components. This is typically the case in unconventional engine configurations like the horizontally-opposed Boxer 4-cylinder, or transversely-mounted V6 configurations.

Needless to say, reaching the spark plugs in the confined spaces of these powertrain configurations can be rather difficult. There are workarounds, however. Removing the windshield washer fluid reservoir on the driver’s side and the airbox on the passenger’s side will give you a straight shot at the spark plugs in the Subaru Boxer configuration, for instance. More complex configurations might require a full dismantling of the engine, though.

Choosing the right replacement spark plugs

The best course of action when choosing the right replacement spark plugs for your car is to go with the OEM plugs. Car manufacturers provide specific information relating to optimal spark plugs, including their type, heat range, size, etc. For instance, you don’t want to buy spark plugs that are longer than the original plugs as they’d end up hitting the piston head, while the shorter ones wouldn’t fire the flame properly.

This doesn’t mean that you absolutely must stick with the original equipment manufacturer or even a plug type for that matter. An upgrade to higher-tier spark plugs won’t do any harm – especially if you’re gunning for some of the best spark plugs on the market. Do bear in mind that your selection remains within the limits imposed by the manufacturer.

However, never downgrade from higher-tier to lower-tier spark plugs (i.e. going for copper core plugs when the manual mandates platinum spark plugs), as that could lead to potentially severe detrimental effects on your car’s engine.

General tips for replacing your spark plugs at home

If you live by the DIY code, here are the steps necessary to successfully replace your car’s spark plugs.

1. Tools and spark plugs

Before starting with the spark plug replacement, it’s advisable to prepare all the tools that you’re going to need and to, of course, buy the right set of spark plugs for your vehicle.

Assuming that your vehicle has an engine with hard-to-reach spark plugs, here are all the tools you’re going to need (not all of them are necessary for simpler powertrain layouts):

  • Your vehicle’s manual
  • Ratcheting socket wrench
  • Socket wrench extension
  • Spark plug socket
  • Flexible handle ratchet
  • Torque wrench
  • Spark plug gap tool
  • spark plug boot pliers
  • Clean rag or paper towels, gloves, safety glasses

2. Take all the necessary safety precautions

Start with parking your car on a flat, dry surface and wait for the engine to cool off. Proceed by cleaning the area around the spark plug location from debris to prevent it from falling into the spark plug pocket once the plugs have been removed. Don’t forget to disconnect your car’s battery (a negative terminal alone should be sufficient)

3. Remove any interfering elements if necessary

As described above, some engines provide a straight shot at spark plugs, while others hide them behind other engine components or covers. This is where the extra tools such as socket wrench extension or flexible handle ratchet will come in handy. Note that you might also need a new gasket if your vehicle necessitates the removal of the upper intake plenum.

4. Remove the spark plug boots or coil on plug boots

When you gain access to the rubber spark plug boots, remove them one by one while keeping track of which one serves which cylinder as cylinders fire in a particular order. If the boot is stuck, use the spark plug boot pliers. Alternatively, you could also use bent-nose pliers but be careful not to damage the rubber boot. If the boot gets damaged or if it already was, a replacement is necessary. Luckily, spark plug rubber boots are inexpensive and not that hard to replace.

Engines with a coil on plug (COP) ignition system use a long insulator boot instead of a traditional spark plug boot. To remove them, disconnect the electrical connector from the ignition coil first by pressing down or pulling up on the locking tab. Finally, remove the hold-down bolt and twist the coil until it gets loose before pulling it out altogether.

5. Remove the spark plugs

Use a spark plug socket with proper extension (if required) to unscrew and remove the spark plugs. If the resistance is particularly strong, try using a penetrant fluid like the WD-40. If the plugs still won’t come out, it’s best to seek professional help as you wouldn’t want to damage the cylinder head. If they do come out as they should inspect them for potential damage, debris buildup, colouration, etc. This should give you an idea of the state of your car’s powertrain.

6. Install the new spark plugs

Most spark plugs are pre-gapped by the manufacturer, and you won’t need to gap them manually before use. Some, however, require this particular step. Check your manual for spark plug gap specifications and adjust them accordingly using the spark plug gap tool.

Carefully set the spark plugs onto the engine by using a plug socket and tighten them with a torque wrench. Be careful not to over-torque or cross-thread the plugs.

7. Re-attach the spark plug boots and all the remaining parts

The last order of business is to essentially repeat the entire process in reverse. Start by reapplying the spark plug boots or COP boots but pay attention to their order. Then proceed to reattach all the components you had to remove before to gain the access to the spark plugs. Finally, don’t forget to reconnect the battery.