(Updated on April 22, 2020)
“A spark plug is just a spark plug” is a common, yet incorrect phrase. Certain spark plugs are more efficient and perform better than others, and each type has a specific use case.
That alone makes it important to check the recommendations of the vehicle manufacturer to ensure the correct spark plugs are installed in your vehicle.
Below is everything you wanted to know about spark plugs including how the 5 most common types of spark plugs compare.
How Spark Plugs Work
The purpose of a spark plug is to ignite the compressed mixture of air and fuel in each cylinder of a gasoline-powered internal combustion engine.
There is an insulated center electrode running the length of the spark plug and one or more ground electrodes on the bottom end, separated from the exposed end of the center electrode by a space known as a spark gap.
When the voltage supplied from the ignition coil to the spark plug is high enough, the electrical energy jumps the gap, forming a spark.
The electrodes were traditionally made of copper but now they are also being manufactured from rare materials like iridium and platinum. Newer spark plugs utilize smaller center electrodes in order to lower the amount of voltage required to generate a spark. Less voltage required makes for a more efficient ignition system.
In most gasoline-powered vehicles, the number of spark plugs is equal to the number of cylinders. However, some high-powered vehicles use two spark plugs per cylinder.
Types of Spark Plugs
The main types of spark plugs are copper/nickel, iridium, single platinum, double platinum, and silver. The best spark plug varies depending on the vehicle. Below you will find more details on each of these spark plugs and what they are good for.
Copper Spark Plugs
The center electrode of this type of spark plug is a copper core coated with a nickel alloy. It has the largest diameter of all the other spark plugs, so it needs more voltage to generate a spark.
Nickel alloy is a material that is soft and not very durable, so the spark plugs will need to be replaced more frequently than other types. Some cars are designed to use copper spark plugs despite their shorter lifespan.
In some of these cases, installing more expensive spark plugs may be a waste of money. Check the owner’s manual for manufacturer recommendations.
- Appropriate for older vehicles built before 1980
- Performs well under high-compression or turbocharged conditions
- Shorter lifespan
- Requires more voltage
Iridium Spark Plugs
Iridium spark plugs last the longest since iridium is harder and more durable than platinum. These spark plugs have a small center electrode which requires less voltage to generate a spark. These advantages are reflected in the higher price tag.
Many car manufacturers are now using iridium spark plugs in their vehicles, so it’s important to stick with iridium when replacing the plugs rather than downgrading to platinum or copper/nickel. That could adversely affect the performance of the vehicle.
- Leads to more complete combustion
- Long lifespan
- Requires less voltage
Single Platinum Spark Plugs
A single platinum spark plug is similar to a copper/nickel spark plug, except that its center electrode has a platinum disc welded to the tip instead of only nickel alloy. The platinum metal lasts longer than nickel alloy before being worn away.
These plugs also generate more heat, which reduces carbon buildup. This is the recommended material for new cars with a coil-on-plug ignition system.
- Long lifespan (up to 100,000 miles)
- Reduces carbon buildup
Double Platinum Spark Plugs
Double platinum spark plugs have platinum coating both the center and ground electrodes. This is more efficient and longer-lasting which makes these plugs a great choice for a wasted spark ignition system, which exerts more wear on both electrodes than do other ignition systems.
In a wasted spark ignition system, each ignition coil fires two spark plugs at once, one in the compression stroke’s cylinder and the other in the exhaust stroke’s cylinder.
The spark for the latter gets wasted because the air-fuel mixture was already burnt on the previous stroke. This ignition system is an improvement over distributor ignition systems because it isn’t affected as much by rain or debris.
- Recommended for wasted spark ignition systems
Silver Spark Plugs
These are less common than others and feature silver-coated electrode tips. These do not last as long as iridium or platinum spark plugs as the metal is less durable. They are most often used in older European performance cars and motorcycles.
- Best thermal conductivity
- Decreased longevity
Spark Plug Gap
The business end of a spark plug is home to the gap, a distance which must be very precise in order for the spark to correctly form. Over time this gap can increase as the metal on the electrodes wears down, so it’s important to measure the gap with a special tool.
The electrodes can be bent to adjust the gap, a process known as gapping.
Sometimes the spark plug is too far gone to repair by gapping and must be replaced. Continuing to use a spark plug with an incorrect gap can cause problems such as engine misfiring, power loss, and poor fuel economy.
Hot vs Cold Spark Plugs
The heat range of spark plugs refers to the temperature of the tip where the gap is found. Hot spark plugs are better insulators which keeps more heat in the tip of the spark plug, and therefore in the combustion chamber.
These tend to last longer than cold spark plugs, because temperatures are high enough to burn off carbon deposits. Hot spark plugs work well in most standard vehicles.
Cold spark plugs are much less insulated so more heat is conducted out of the tip and away from the combustion chamber to the outside of the engine, keeping the combustion chamber cooler.
Cylinder chambers that are too hot for ideal function can lead to issues such as pre-ignition or knocking (uneven fuel burn) which can result in permanent engine damage.
These plugs are ideal for high-performance vehicles with high-temperature engines, such as those with high horsepower, high RPM, prolonged acceleration or high-speed driving, or forced induction.
Regular vs Performance Spark Plugs
All of the above metals can be used to make either regular (replacement) or performance spark plugs. Performance spark plugs are tougher, able to withstand a greater change in temperatures and mechanical stress than replacement spark plugs.
This is useful for cars which are driven hard, as the engines are under much more stress than those in engines driven under normal conditions.