How to Determine the Condition of Spark Plugs?
3 Answers
Methods to determine if spark plugs need replacement: Remove the spark plugs and observe their appearance color to assess their condition. Normal spark plugs have insulator skirts and electrodes that 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 is covered in oil or deposits but 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, the air-fuel mixture is too rich, or there is oil leakage. Damaged spark plugs can directly cause issues such as electrical leakage in the vehicle's ignition system, increased fuel consumption, reduced power, and most notably, difficulty in starting, affecting the vehicle's normal operation. Severe erosion of the spark plug, including blistering at the top, damage, or melted and eroded electrodes, indicates the spark plug is ruined and should be replaced.
Last time my car had weak acceleration and idling vibration, so I suspected the spark plugs might be faulty. When checking them yourself, it's best to remove them for inspection after the engine is turned off and cooled down. If the electrode tips are severely worn, the gap has widened, or there's thick black carbon buildup, they're definitely bad. Normal spark plugs should be light brown or grayish-white in color. If you notice melting, cracks, or oil stains, replace them immediately. Don't underestimate them – poor ignition can make your car consume more fuel, increase emissions, and even damage the engine in the long run. I usually check them every 50,000 to 60,000 kilometers to ensure safety and peace of mind. If you find any issues, don't hesitate – a new set only costs a few dozen bucks, which is much better than breaking down on the road. Paying attention to routine maintenance can extend your car's lifespan.
I often DIY car repairs, and judging spark plug condition is quite straightforward: use a regular wrench to unscrew the spark plug, hold it in your hand and carefully inspect the electrode part—a gap of around 0.8mm is ideal, if it's too large, it needs adjustment or replacement. Oil stains, blackening, or a rounded center electrode all indicate it's bad. A simple test method: connect it to the ignition wire, start the engine and see if the spark is blue and even; if it's weak, it's no good. Keep a multimeter handy to measure resistance, which should be within the normal range of 5-15 kilohms. Checking it yourself is fun and saves money, but don't forget to discharge static electricity to prevent shocks. Ordinary household tools will do, and watching online tutorial videos is safer. Before replacing, make sure the brand matches to avoid misfires from using the wrong type.
