Spark Plug

A spark plug is a small, threaded device screwed into the cylinder head of an internal combustion engine. Its primary role is to receive high-voltage electrical current from the ignition coil and produce an electrical spark across a small gap at its tip, igniting the compressed air-fuel mixture within the cylinder.

Spark plugs consist of a metal threaded shell, a central electrode insulated by ceramic, and a ground electrode. The distance between the central and ground electrodes—known as the spark plug gap—must be set precisely to ensure a strong, reliable spark. Spark plugs are manufactured with different electrode materials, including copper, platinum, and iridium, which offer varying lifespans.

Over miles of driving, spark plug electrodes gradually wear down from spark erosion, widening the gap and requiring higher voltage to fire. Spark plugs can also become fouled by carbon deposits, oil, or coolant leaks. Worn or fouled spark plugs lead to engine misfires, a rough idle, poor acceleration, decreased fuel economy, and hard starting.

Regular spark plug replacement is a fundamental part of engine tune-up maintenance. Standard copper plugs may require replacement every 30,000 miles, while long-life double-platinum or iridium plugs can last up to 100,000 miles or more.