How Often Should Spark Plugs Be Replaced, Based on Mileage?
2 Answers
Spark plug replacement is typically based on mileage. Under normal maintenance conditions, they should be replaced after driving 40,000 to 60,000 kilometers. However, this may vary depending on the brand and engine type, so it's recommended to follow the user manual. Platinum spark plugs should be replaced at 40,000 kilometers, standard nickel alloy spark plugs at 20,000 kilometers, and iridium spark plugs at 60,000 to 80,000 kilometers. Methods to determine if spark plugs are damaged: Remove the spark plug and observe its condition based on the following appearance and color. A normal spark plug's insulator skirt and electrodes should appear gray-white, gray-yellow, or light brown. A properly functioning spark plug has a reddish-brown insulator skirt, with an electrode gap between 0.8-0.9mm and no signs of electrode burn. If the spark plug has oil stains or deposits but is not damaged, it can continue to be used after cleaning off the oil and deposits. If the spark plug is severely damaged, showing signs like blistering at the top, black streaks, cracks, or melted electrodes, the cause of the damage should be identified. After troubleshooting, replace the spark plug with a new one. Additionally, if the spark plug appears black as if smoked, it indicates the wrong heat range was selected or the air-fuel mixture is too rich, with oil creeping up.
Spark plug replacement is typically based on mileage, but the actual situation depends on specific driving conditions. Having driven for over a decade, my experience is that most vehicle manuals recommend a mileage range—say, between 30,000 to 80,000 kilometers. The reason is that spark plug wear is directly affected by driving habits: frequent short trips in city traffic with heavy congestion lead to faster carbon buildup and shorter lifespan, while highway cruising causes less wear. Material also plays a key role—copper plugs are cheaper but last only 20,000–30,000 km, while platinum or iridium plugs cost more but can exceed 100,000 km. If a car sits idle for long periods, the plugs can degrade over time regardless of mileage. I suggest having a technician inspect the spark plugs during each maintenance check. Address issues like difficulty starting or sudden spikes in fuel consumption immediately to avoid minor problems escalating into major repairs. Overall, combining mileage with actual symptoms is the most reliable approach—don’t skimp on maintenance to save a few bucks.
