A vital part of a vehicle's ignition system, spark plugs use one of three conductive metals. Spark plugs ignite the combustion chamber's fuel-air mixture and channel the high-voltage electricity to each engine cylinder head. A four-cylinder vehicle has four spark plugs, and six-cylinder and eight-cylinder vehicles have six and eight spark plugs, respectively. The metal core should conduct electricity without overheating and compromising its operation. Depending on the engine type, longevity needs, and cost considerations, drivers can select spark plugs that use iridium, copper, or platinum cores.
Spark plug basics
In a vehicle's ignition system, the ignition coil amplifies the powerful spark to the spinning distributor, which sends the spark to each spark plug. By the time the electric current from the distributor reaches the spark plug connector, its voltage ranges from 40,000 volts to 100,000 volts.
A nonconductive ceramic insulator surrounds the metal core, preventing the voltage from sparking before it reaches the electrode on the other side. Car and truck owners should use the spark plugs recommended in the owner's manual for the engine and ignition system in their vehicle.
Spark plug gap
At the other end of the plug, the spark jumps from the central electrode across the tiny, precisely measured gap to the lateral electrode that conducts the voltage to the cylinder. There, it ignites the fuel-air mixture that powers each cylinder. Auto professionals and mechanically inclined owners can measure this gap with a precision spark plug gap tool and adjust it if it is too wide or too narrow.
In addition to replacing spark plugs at the recommended intervals for each type, owners should also replace them when they become worn or begin misfiring. Owners should replace their spark plugs immediately if carbon tracking occurs, which is when the spark fires between the top and base of the spark plug on the ceramic shell's exterior. Also, hot gases from compression leakage can damage a car's ignition coils, requiring immediate spark plug replacement.
Iridium spark plugs
Iridium is the hardest conductive metal used in spark plugs, measuring 6.5 on the Mohs hardness scale out of a possible 10. Iridium spark plugs last for a long time, approximately twice as long as copper.
Iridium plugs can reduce the frequency of misfires, which can improve horsepower and fuel efficiency. These plugs have a wider heat range and a lower voltage requirement to produce the same spark as copper spark plugs. Iridium spark plugs are not recommended for use in modified engines. Depending on the brand and car make, owners should replace them every 48,000 km to 81,000 km.
Copper spark plugs
Copper is the softest metal used in spark plugs, measuring 2.5 to 3 out of 10 on the Mohs hardness scale. Copper spark plugs are the least likely of all conductive metals to overheat, which lowers the tip's temperature. An overheated metal core can damage the components inside the plug, which can interrupt or delay the spark's delivery to the cylinder.
Regarded as having the most efficient performance of any spark plug, copper spark plugs are highly conductive, increase the plug's longevity, and are good matches for high-performance or modified engines. Copper spark plugs are manufactured with standard-sized gap sizes, which owners can widen with a gap tool to optimise the plug's efficiency and fuel economy. Copper is a relatively soft metal, requiring spark plug replacement about every 48,000 km, or as recommended by the owner's manual.
Platinum spark plugs
Platinum is a hard metal, measuring 4.5 on the Mohs hardness scale, slightly lower on the scale than iridium. The other hard metals — titanium, hardened steel, tungsten, and tungsten carbide — are harder, but they are not good conductors of electricity.
Platinum spark plugs are less conductive than copper spark plugs, and are not generally recommended for use with supercharged engines. Drivers often choose platinum spark plugs for their longevity, and they should be replaced every 48,000 km to 60,000 km, or as recommended in the owner's manual.
How to buy spark plugs on eBay
Selecting the right spark plug for your vehicle ensures it starts and runs reliably and smoothly. Enter the kind of spark plug or tool you need into the search window on any eBay page, such as "iridium spark plug" or "spark plug tester". You can enter a general search term such as "spark plugs" and browse the results or narrow your focus by car make. Once you find the right spark plugs for your vehicle, you can install a new set and keep a spare set on hand.