* Worn Valve Stem Seals: These seals prevent oil from leaking past the valve stems into the combustion chamber. If they're worn, oil can seep past and be burned, leading to oil fouling on the plugs. This is a common problem in higher-mileage cars like a '98 Neon.
* Worn Piston Rings: Piston rings seal the combustion chamber. If they're worn, oil can leak past into the combustion chamber, again leading to oil on the plugs. This is a more serious issue than worn valve stem seals and usually indicates significant engine wear.
* Failing PCV Valve: The PCV valve is part of the crankcase ventilation system. It allows blow-by gases (pressure buildup from the crankcase) to be recirculated back into the intake manifold. A faulty PCV valve can cause excessive crankcase pressure, forcing oil past seals and into the engine. This is a relatively inexpensive and easy part to replace.
* Crankcase Pressure Issues: Even with a working PCV valve, excessive crankcase pressure (due to other issues like blocked breather hoses or a failing oil pressure sensor) can push oil past seals.
* Head Gasket Leak (Less Likely but Possible): While less likely to directly cause oil *on* the plugs, a blown head gasket can allow oil to mix with coolant or vice versa, and contribute to overall engine oil contamination. This would likely present with other symptoms as well.
What to do:
1. Check the PCV valve: This is the easiest and cheapest thing to check and replace first. It's a small, relatively inexpensive part, and a failing PCV valve is a common culprit.
2. Inspect the spark plug wells: Make sure there isn't excessive oil accumulation in the spark plug wells themselves. This can indicate more serious issues like a cracked valve cover.
3. Consider a compression test: This will help assess the condition of your piston rings and valves. Low compression in one or more cylinders points to significant wear.
4. Leakdown test: A leakdown test will pinpoint exactly where compression is escaping, further diagnosing the source of the oil contamination.
5. Consult a mechanic: If you're not comfortable performing these checks yourself, a qualified mechanic can diagnose the problem accurately and recommend the appropriate repairs. The cost of repair will depend significantly on the root cause. Replacing the PCV valve is inexpensive, but replacing piston rings or valve stem seals requires more extensive engine work.
Ignoring this issue can lead to further engine damage, including:
* Pre-ignition: Oil on the plugs can cause misfires and pre-ignition, potentially damaging the engine's internal components.
* Damaged Catalytic Converter: Unburnt oil can damage the catalytic converter, a very expensive part to replace.
Don't drive the car extensively with this problem. Get it checked out soon.
