Spark Plugs: What Are They and Why Are They Important?

What are Spark Plugs?

Spark plugs are insulated plugs that are screwed into an internal combustion engine’s cylinder head to deliver the spark that ignites the mixture of air and fuel in the combustion chamber. In the case of diesel engines, thanks to its high compression ratio and the nature of diesel oil, it ignites without any aid from spark plugs.

Example of a spark plug from BE FORWARD.

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Spark plugs also transfer heat away from the combustion chamber. Basically this is what happens: the spark plugs are placed at the top of the cylinder head in most of engine types, the piston first travels down the cylinder, drawing in a mixture of fuel and air. The piston then goes back up toward the spark plug, compressing the mixture. At the very last second, when the piston is at its fullest reach on the top of the cylinder, the spark plug sparks and ignites the mixture.

The piston is forced back down to create power for the vehicle by way of crank shafts and drive shafts to the wheels. At that point, the process of firing the engine ends and starts all over again to continuously give power to the vehicle.


Types of Spark Plugs

A four-cylinder car will have four (eight) spark plugs; a six-cylinder car will have six (twelve) and so on, though a HEMI; Hemispherical V-shape engine has two plugs per cylinder. Now that we’ve got the basics down, let’s talk about the kinds of spark plugs that are generally sold.

Standard spark plugs in modern engines have a copper center electrode core surrounded by a nickel alloy, which you can see at the tip of the plug. Inside the plug, the center electrode is encased in porcelain, which helps transfer heat from the engine to the cooling system. Premium spark plugs make use of precious metals, like platinum or iridium, in place of the nickel alloy.

Laser Iridium spark plugs - BE FORWARD

Above: Premium grade Laser Iridium NGK spark plugs

These metals have higher melting points, and higher prices to match. In most high-priced or sporty vehicles at least platinum is used, furthermore, thanks to its durability and high igniting performance, iridium has been replaced by platinum these days.

The disadvantage of regular copper head is its durability. The cheaper the material is, the less durability we can expect from the spark plug. The copper ignites at a lower temperature, but it lasts much less than platinum and iridium. Speaking of temperatures, spark plugs come in two basic varieties: cold and hot. Cold plugs work best in high-horsepower high-compression engines. They have less insulation, so more heat can be transferred away from the combustion chamber to the outside of the engine.

Hot plugs have more insulation and are found in most standard engines. The extra insulation keeps the plug’s temperature high enough to burn off carbon deposits, which allows for more time between spark plug changes.

When to Replace Spark Plugs

How do you know if your plugs need to be changed? It is difficult to know the appropriate time for the change from your eyes alone, because they are all hidden on the upper side of the engine. The surest sign we recommend is to check your odometer. Spark plugs usually need to be changed every 48,000 kilometers.

Some high-performance plugs can go as long as 160,000 km before replacement, but this is not always the case. If you don’t know when yours were last changed or if you have an engine that runs roughly (knocking sometimes represents the phenomenon) or has recently showed a noticeable decrease in fuel economy, it could mean that your engine might benefit from new and higher quality spark plugs. As always, it is recommended to check the owner’s manual to see what works best for your vehicle.

New and used spark plug examples - BE FORWARD

Above Left: A new Iridium plug / Above Right: Regular plug with over 30,000km mileage

(Left; new Iridium plug and Right; regular plug with over 30,000km mileage)

The price of spark plugs differs mainly from its raw material (metal) used for electrode cores. The copper is regularly used for its relatively high performance compared to any spark plug type thanks to its conductivity and cheaper in price for its natural resource abundancy (copper). Next comes platinum as is well known precious metal for its longevity compared to copper, which is recently ranked next to iridium because it generates better performance when it’s used for electrode cores.

Iridium is a chemical element with the atomic symbol “Ir” and atomic number 77. A very hard and silvery-white transition metal of the platinum group, iridium is generally credited with being the second densest element (after osmium) based on measured density, although calculations involving the space lattices of the elements show that iridium is denser. It is also the most corrosion-resistant metal, even at temperatures as high as 2000 °C. Be sure to check which kinds of spark plugs are compatible with your vehicle before purchase.

Although it is usually recommended to have a professional replace your spark plugs, it is also possible to replace them yourself fairly quickly if you follow the instructions on how to replace your spark plugs closely.

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