What Causes the Reddish-Brown Color on the Spark Plug Tip?
3 Answers
The reddish-brown color on a spark plug is caused by early ignition timing or a lean air-fuel mixture. Methods to determine if a spark plug is damaged: Remove the spark plug and observe its appearance to assess its condition. 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 is coated with oil or deposits but is otherwise undamaged, 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 tip, black streaks, cracks, or melted electrodes—the cause of the damage should be identified and the issue resolved before replacing the spark plug. 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 engine oil is entering the combustion chamber.
The spark plug head appears reddish-brown, and I've encountered this situation many times. It is usually caused by excessively high engine temperatures, where the spark plug electrodes and insulators oxidize and discolor when overheated. Common causes include an overly lean air-fuel mixture (too little gasoline and too much air), leading to excessively violent combustion and temperature spikes; ignition timing set too early can also cause premature combustion and temperature rise; cooling system issues such as a non-functioning fan or water pump failure result in poor heat dissipation. Additionally, mismatched spark plug heat ranges or the use of low-quality fuel can exacerbate the discoloration problem. If ignored for a long time, the spark plug insulation deteriorates, causing misfires or failure to ignite, resulting in engine shaking and poor acceleration. For prevention, it is recommended to regularly check the coolant level, avoid parking immediately after prolonged high-speed driving, use standard gasoline to adjust the ignition timing, and ensure the correct spark plug model is selected when replacing them—avoiding cheap alternatives. During maintenance, it's best to visit a professional shop to read computer data, ensuring a healthy air-fuel mixture ratio.
The spark plug tip turning reddish-brown is a common issue I've encountered over 20 years of truck driving. The primary cause is overheating and oxidation during engine operation. Specifically: an excessively lean air-fuel ratio raises combustion chamber temperatures, often due to insufficient fuel supply from a dirty fuel pump or clogged injectors; excessive ignition advance causing premature combustion also increases temperatures; loose fan belts or clogged radiators impair cooling. This accelerates spark plug aging, leading to unstable ignition, engine stalling, and even knocking risks. Immediate action involves checking the cooling system and intake pipes, cleaning carbon deposits, and replacing the air filter. If the heat range is incorrect, simply replace with suitable spark plugs. Avoid prolonged overload driving which raises temperatures - allow cooldown by idling for several minutes before shutdown. Never ignore discoloration warnings for safety. Proper maintenance restores smooth engine operation and improves fuel efficiency.
