- Worn piston rings: Worn piston rings can allow oil to seep past the pistons and into the combustion chamber, where it can foul the spark plugs.
- Leaking valve seals: Leaking valve seals can also allow oil to seep into the combustion chamber, causing the spark plugs to become fouled.
- Clogged PCV (positive crankcase ventilation) valve: If the PCV valve is clogged, it can cause pressure to build up in the crankcase, forcing oil past the piston rings and onto the spark plugs.
If you find oil on your spark plugs, it's important to identify and correct the underlying cause before replacing the spark plugs. Otherwise, the new spark plugs will likely become fouled again.
In some cases, it may be possible to clean the spark plugs and reinstall them. However, if the oil is due to worn piston rings or leaky valve seals, the spark plugs will need to be replaced.
