What Causes Oil on Spark Plugs?
2 Answers
The presence of oil on spark plugs is typically due to quality issues with the spark plugs themselves, necessitating replacement with new ones. Steps for replacing spark plugs: Open the engine hood, lift the plastic engine cover, and remove the high-voltage distributor wires. Mark each cylinder's position to avoid confusion. Use a spark plug socket to remove the spark plugs one by one. During removal, check for external debris like leaves or dust and ensure thorough cleaning. Place the new spark plug into the spark plug hole, hand-tighten it a few turns, then use the socket to fully tighten. Reinstall the high-voltage distributor wires according to the firing order and secure the cover. Methods to determine if a spark plug is damaged: Remove the spark plug and inspect its appearance to assess its condition. A normal spark plug's insulator skirt and electrodes appear gray-white, gray-yellow, or light brown. A properly functioning spark plug has a reddish-brown insulator skirt, with electrode gaps between 0.8-0.9mm and no signs of electrode burning. If the spark plug is soiled with oil or deposits but otherwise undamaged, it can continue to be used after cleaning. If the spark plug is severely damaged—showing signs like blistering, black streaks, cracks, or melted electrodes—identify the cause of the damage, rectify the issue, and replace the spark plug. Additionally, if the spark plug appears black as if smoked, it indicates incorrect heat range selection, a rich fuel mixture, or oil leakage.
When I used to repair cars, I often saw oil on the spark plugs, which is usually caused by internal engine sealing issues, such as a leaking cylinder head gasket or worn piston rings. The flow of oil is like a cracked water pipe—it leaks into the combustion chamber and sticks to the spark plugs. Worn piston rings compromise the seal, allowing oil to seep in; an aging cylinder head gasket is also prone to leaks. The problem may also stem from a faulty valve cover seal. This can lead to poor ignition, engine shaking, increased fuel consumption, and even excessive emissions. Remember to always check the engine temperature after replacing the spark plugs, as overheating can accelerate wear. Don’t underestimate this issue—delaying repairs may cause more severe engine damage. It’s best to have a professional technician diagnose the problem promptly. For prevention, I make it a habit to inspect the spark plugs during every oil change. This helps detect sealing issues early and avoids breakdowns on the road.
