Inside every petrol engine, the spark plug delivers the precisely timed electrical discharge that ignites the compressed air-fuel mixture in each cylinder. It screws into the cylinder head, sealing combustion pressure while exposing its electrode tip to temperatures that can exceed 800 °C during normal operation. When a spark plug deteriorates, the electrode gap widens through erosion, the dielectric insulator can crack, or deposits build up on the tip — any of which can cause a misfire. A misfiring cylinder passes unburnt fuel into the exhaust, triggering the engine management warning light, raising hydrocarbon emissions, and over time damaging the catalytic converter. Replacement intervals depend heavily on electrode material: standard copper-core plugs are typically changed every 30,000 miles, while iridium and platinum designs found on modern engines can last 60,000 miles or more. NGK and Denso are the dominant suppliers to vehicle manufacturers worldwide and publish OE cross-references that link their part numbers directly to the original equipment specification for each engine variant. Because thread pitch, reach, and heat range are all engineered for the specific cylinder head geometry, matching the OE number is essential — fitting the wrong heat range in particular can cause pre-ignition or fouling that shortens plug life dramatically.
Spark plugs are engine-specific: thread diameter, reach, hex size, and heat range all vary between engine families. Each listing on this page shows the OE references TecDoc maps to exact engine variants. Cross-reference using your vehicle's make, model, engine code, and build year. Even two engines from the same manufacturer can require different heat ranges depending on turbocharging and compression ratio, so using the OE number rather than a generic 'fits all' listing avoids the risk of fouling or pre-ignition damage.
OEM spark plugs are manufactured by specialist suppliers — principally NGK, Denso, and Bosch — to the vehicle builder's exact heat-range and electrode specification. Quality aftermarket equivalents from the same names carry the identical OE cross-reference and perform to the same standard. Generic unbranded plugs may use lower-grade electrode alloys that wear faster, widening the gap ahead of schedule and causing intermittent misfires before the scheduled service interval is reached.
Service intervals depend on electrode material. Standard copper-core plugs — common on older or budget engines — are typically due at 20,000–30,000 miles. Platinum-tipped plugs extend this to around 40,000–50,000 miles. Iridium plugs, now fitted as standard to most modern petrol engines, can reach 60,000 miles or beyond if the engine burns no oil and runs on quality fuel. Always follow the manufacturer's service schedule for your specific engine rather than relying on generalised figures.
The most obvious symptom is an engine misfire — felt as a rhythmic judder at idle or a hesitation under acceleration. The engine management warning light often illuminates alongside, particularly if the ECU detects a misfire in a specific cylinder. Other signs include difficulty starting from cold, noticeably higher fuel consumption, and in severe cases a rough idle that the engine cannot stabilise. Removing a plug and inspecting the tip will reveal heavy fouling, a cracked insulator, or a visibly eroded electrode that confirms replacement is due.
Showing 100 of 10,307 Spark Plug OE numbers. Enter the OE on the main OE search to jump to any reference.
