What are the reasons for spark plugs turning black?
2 Answers
The most common reason for spark plugs turning black is poor combustion. The black substance is caused by carbon deposits and burning engine oil. Working principle of spark plugs: Under high voltage, the air between the center electrode and side electrode of a spark plug rapidly ionizes, forming positively charged ions and negatively charged free electrons. When the voltage between electrodes reaches a certain level, the number of ions and electrons in the gas increases like an avalanche, causing the air to lose its insulating properties and forming a discharge channel between the gap, resulting in a "breakdown" phenomenon. At this point, the gas forms a luminous body, known as a "spark." Accompanied by thermal expansion, a "crackling" sound is also produced. The temperature of this electric spark can reach 2000-3000°C, sufficient to ignite the air-fuel mixture in the engine cylinder. Spark plug replacement cycle: Under normal maintenance conditions, replacement is recommended after driving 40,000 to 60,000 kilometers. However, this may vary depending on the brand and engine type, so it's advisable to follow the user manual. The following standards can be referenced for maintenance replacement: Platinum spark plugs should be replaced at 40,000 kilometers, ordinary nickel alloy spark plugs at 20,000 kilometers, and iridium spark plugs at 60,000-80,000 kilometers.
I was quite alarmed when I noticed the spark plugs turning black, especially since the car was relatively new. This usually indicates an internal engine issue, such as engine oil leaking into the combustion chamber, causing oil residue to accumulate on the spark plugs. Alternatively, it could be due to an imbalance in the fuel-to-air ratio, where a dirty air filter leads to an overly rich air-fuel mixture and incomplete combustion. Daily driving habits also play a role—like my frequent short trips in the city, where the engine barely warms up before being shut off, leading to carbon buildup on the spark plugs. Over time, this not only makes ignition difficult but also increases fuel consumption, emits black smoke, and compromises driving safety. Replacing the spark plugs and cleaning the air system can help, but it's best to visit a professional shop to check for oil leaks to prevent minor issues from turning into major repairs.
