Judging Spark Plug Condition by Color?
2 Answers
Methods for judging spark plug condition by color: A normal spark plug's insulator skirt and electrodes should appear grayish-white, grayish-yellow, or light brown. A properly functioning spark plug will have a reddish-brown insulator skirt. Methods for determining if a spark plug is damaged: Remove the spark plug and observe its condition based on the following color indicators. A normal spark plug's insulator skirt and electrodes should appear grayish-white, grayish-yellow, or light brown. A properly functioning spark plug will have a reddish-brown insulator skirt, with electrode gap between 0.8-0.9mm and no signs of electrode burning. If the spark plug has oil stains or deposits but isn't damaged, it can continue to be used after cleaning off the oil and deposits. If the spark plug is severely damaged with symptoms like blistering at the tip, black streaks, cracks, melted electrodes, etc., the cause of damage should be identified. After troubleshooting, replace with a new spark plug. Additionally, if the spark plug appears smoke-blackened, it indicates either incorrect heat range selection or rich fuel mixture, possibly with oil leakage.
The color change of spark plugs can reveal engine conditions. Having driven older cars for many years, I rely on this to predict faults. The normal color is an even light brown, indicating complete combustion and high efficiency. Once it turns black, it may be due to an overly rich fuel mixture or a clogged air filter, increasing carbon deposits and fuel consumption. If not addressed promptly, it can damage the spark plugs. A white color indicates overheated electrodes, premature ignition, or a too-lean fuel mixture, which can easily cause stalling at high temperatures. Wet black spots are often caused by oil leakage, which is both wasteful and polluting. I check the color during every maintenance session. If abnormal, I prioritize cleaning or replacement to avoid breakdowns that could disrupt my trip. Simply put, regularly observing spark plugs can extend their lifespan and save money.
