What Causes Oil on Spark Plugs?
2 Answers
The presence of engine 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, and then use the socket to fully tighten it. Reinstall the high-voltage distributor wires in the correct firing order and secure the cover. Methods to determine if a spark plug is damaged: Remove the spark plug and inspect its appearance. 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 remains undamaged, it can be cleaned and reused. 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 sooty black, it indicates incorrect heat range selection, a rich fuel mixture, or oil leakage.
Oil on the spark plug usually indicates an issue with the engine, most commonly caused by engine oil leaking into the combustion chamber. Possible reasons include a deteriorated valve cover gasket allowing oil to drip onto the spark plug, or severely worn piston rings inside the engine, which let oil seep upward around the spark plug. This condition can lead to ignition failure, causing difficulty starting the car and poor acceleration. Over time, the spark plug may corrode and become damaged. When I worked as a mechanic, I often advised car owners to first check if the valve cover is properly sealed, then inspect the piston components by disassembling the engine. If left unrepaired, engine oil consumption will increase, and more severe issues may arise, such as cylinder damage requiring major repairs. Therefore, if you notice oil stains on the spark plug, it's best to visit a professional repair shop promptly for diagnosis and replacement of the affected parts to avoid breakdowns. Regular engine maintenance, including oil and spark plug changes, can effectively prevent such problems.
