Posts Tagged: oil on the spark plug and threads

Oil on spark plugs and threads — The Most Common Cause

What Causes Oil on the spark plugs and threads In my experience, when you find oil on the spark plugs or on the spark plug threads on an overhead cam engine, the cause is always failed spark plug tube seals. On late-model engines, the spark plugs sit deep inside the cylinder head inside a spark plug tube. A rubber spark plug tube seal fits into the valve cover and is designed to prevent oil from leaking into the spark plug tubes. Over time, these spark plug tube seals degrade, allowing … Read More