Spark Plug Buyer's Guide
- A spark plug is one of the first components that activates in your car the moment you press the ignition switch.
- Spark plugs ignite the gasoline and air that are supplied in the combustion chambers.
- A spark plug is a small device typically made of high-nickel alloys, aluminum oxide ceramic, and steel wire.
- A spark plug also acts as a heat exchanger.
- A typical spark plug has at least eight subparts: two electrodes, an insulator tip, threads, a gasket, shell, insulator, and a terminal.
- There are four types of spark plugs: copper, iridium, platinum, and double platinum.
- The most common spark plug issue is a fouled spark plug due to grime deposits, which can happen if there’s always oil on the spark plug.
- A bad spark plug can lead to poor fuel economy, lack of power especially during acceleration, difficulty starting, misfire, and bad idling behavior.
- A spark plug replacement costs from $9 for a single piece, to up to $112 for a set of eight.
A spark plug is one of the first components that activates in your car the moment you press the ignition switch. It will work constantly for as long as your engine is running.
Spark plugs ignite the gasoline and air in the combustion chambers. This buyer’s guide will help you pick the best replacement spark plug for your vehicle.
What is a spark plug?
A spark plug is a small device typically made of high-nickel alloys, aluminum oxide ceramic, and steel wire. It's one of a vehcile's smallest but most crucial components. Spark plugs mount right on top of the cylinder and are crucial for giving your engine the spark it needs to ignite the fuel as it's compressed. The spark plug does this by creating a tiny arc of electric charge between the two electrodes found on its tip.
A spark plug also acts as a heat exchanger. It absorbs excessive thermal energy and passes it to the cooling system.
How does a spark plug work?
A typical spark plug has at least eight subparts: two electrodes, an insulator tip, threads, a gasket, shell, insulator, and a terminal. The assembly hooks up to a high-voltage power source, which is the ignition coil. The electric current coming from the coil causes a voltage difference between the center and side electrodes, leading to a spark.
Before a spark is born in between the two electrodes, the gas between the gap needs to get ionized. For this to happen, the voltage needs to surpass the dielectric strength of the gas. This can only happen as the voltage rises. Ionized, the gas can now act as a conductor and allow the electrons to transfer from one electrode to the other, forming an arc across the gap. The gas then expands as the temperature in the spark channel rises and causes a small explosion.
Combustion happens when the small explosion caused by the expanding gases in the spark channel comes in contact with the compressed fuel and air mixture. A larger ball of fire takes place, which pushes the piston down so that the process can start again. Spark plugs must be rigid and heat-resistant, because this process repeats thousands of times in a single minute.
Types of spark plugs
There are four types of spark plug: iridium, copper, platinum, and double platinum.
Copper Spark Plugs
Copper is an old spark plug material, although quite a number are still being sold. This type features a core mostly made from copper, with nickel alloy as its central electrode. This small subcomponent is its weakness, as nickel alloy isn't as durable compared to other types of metal.
Copper spark plugs should last around 20,000 miles. If they fail too soon, it might be a sign that you need to check the condition of related parts and systems. The way you drive your vehicle, the roads or terrain you typically drive on, and your vehicle's model can all impact the actual lifespan of your copper spark plugs.
Copper spark plugs don't last for very long. They work best when used in older vehicles, as these old cars don’t need a high electrical supply.
Platinum Spark Plugs
Platinum spark plugs also feature a copper core. But copper spark plugs have nickel alloy tips instead of a platinum disc found on platinum spark plugs. Platinum is harder than nickel alloy, with a melting point of up to 3,215 degrees Fahrenheit.
If your car features an electronic distributor-based or distributorless ignition system (DIS), we recommend that you use a platinum spark plug.
Double-Platinum Spark Plugs
A double platinum spark plug has an additional platinum disc on the bottom of the side electrode. This reinforces the side electrode, like a platinum cap strengthens the copper core. Double-platinum spark plugs allow the spark to jump back from the side electrode to the central electrode. The platinum on the side electrode enables it to handle reverse spark. The return of spark is crucial if you have a wasted-spark DIS.
If your car's already using a double-platinum spark plug, don’t try to downgrade to a single platinum plug. Single platinum plugs lack a side electrode that can handle a reverse spark.
Iridium Spark Plugs
Iridium is harder than copper and platinum, so expect iridium spark plugs to last the longest. These feature a fine iridium tip welded onto the fine wire electrode core. They're some of the best spark plugs on the market. There’s also a variety with a platinum disc welded on the side electrode for coil-on-plug (COP) system compatibility.
Given the size of the iridium material, this spark plug doesn’t require huge voltage to generate a spark. This means that they're more efficient than other types. The only downside is that iridium is an expensive metal. Even after reducing the electrode size to as little as 0.4 mm, aniridium spark plug is still the most expensive option.
What causes a bad spark plug?
Spark plugs can fail because of several reasons. If there’s always oil on the spark plug, this part can be fouled by grime deposits. When spark plugs fail, you will experience multiple performance and comfort issues with your vehicle.
To learn more about cleaning a spark plug, read our article.
A bad spark plug can lead to poor fuel economy, lack of power, especially during acceleration, difficulty starting, misfire, and bad idling behavior. If you notice some of these symptoms, have your car checked by a certified mechanic as soon as possible.
Choosing the Right Spark Plug
Selecting the right spark plug is a crucial decision. Here are some things that you should consider.
What to look for in your spark plug?
Durability dictates the lifespan of your spark plug. You won't get your money's worth if it isn't made to withstand wear and tear.
Fit will dictate the ease of your installation process. Installing a spark plug isn't compliacted, as long as you buy one that matches your vehicle's specific make and model.
Copper vs Platinum vs Iridium
Which of these three is the best material for your spark plug? Here's a list of the melting points and lifespan of each material:
- Melting point: 1, 983 degrees F
- Lifespan: 15, 000 - 20, 000 miles
- Melting point: 3, 222 degrees F
- Lifespan: 30, 000 - 60, 000 miles
- Melting point: 4, 229 degrees F
- Lifespan: 60, 000 - 100, 000 miles
Buy a copper spark plug if you want one that's a good electric conductor. Platinum or iridium spark plugs will last longer.
If you're looking for information about how to change apark plugs, you may read our article here.
How much are spark plugs?
CarParts.com sells some of the most affordable and reliable OE spark plug replacements on the market. A spark plug replacement can cost from $9 for a single piece, while a set of eight can cost $112. Enter your vehicle’s year, make, and model into our vehicle selector to find the most compatible spark plugs for your vehicle.