How to Determine if Spark Plugs Need Replacement
2 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. Properly functioning spark plugs have insulator skirts that are reddish-brown, with an electrode gap between 0.8-0.9mm and no signs of electrode burn. If the spark plugs are covered in oil or deposits but are not damaged, they can continue to be used after cleaning off the oil and deposits. If the spark plugs are severely damaged, with signs such as blistering at the top, black streaks, cracks, or melted electrodes, the cause of the damage should be identified and the issue resolved before replacing the spark plugs. Additionally, if the spark plugs appear blackened as if smoked, it indicates the wrong heat range was selected or the air-fuel mixture is too rich, with 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 importantly, difficulty in ignition, affecting the vehicle's normal operation. Severe spark plug erosion, blistering at the top, damage, or melted and eroded electrodes all indicate that the spark plugs are ruined and should be replaced.
When my old Accord starts jerking while running, it's a clear sign to check the spark plugs. Last week, it failed to start three times in a row during cold starts, and when towed to the repair shop, a set of spark plugs with completely worn-out electrodes was found, with gaps nearly double the factory standard. Normally, waiting at a red light feels like the steering wheel is tap-dancing, the fuel consumption suddenly increased by 2 liters, and acceleration feels like stepping on cotton with no power—all classic symptoms. The mechanic taught me to inspect them every 30,000 kilometers: severe electrode erosion, ceramic body cracks, or black carbon buildup all mean they need replacement. Different materials have vastly different lifespans—ordinary nickel alloys last 30,000–40,000 kilometers, while iridium can go up to 80,000. If unsure, the easiest way is to go to the shop and read the trouble codes.
