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What does oil on a spark plug mean?
My engine keeps misfiring, so I decided to take a look for myself. It seems like there’s some oil on my spark plugs, but I’m not sure where it could be coming from. What does oil on a spark plug mean, in terms of car problems?
Kathryn Mae Kurlychek · Updated on
Reviewed by Shannon Martin, Licensed Insurance Agent.
If you notice oil on your spark plugs, it could mean there’s a leaky valve or gasket somewhere under your hood. Over time, excessive heat and natural wear and tear to gasket heads or valve covers can cause leaks that spew directly into your spark plug holes.
In other cases, the damage may wind up being more severe. Here are a few other common reasons you may find oil on a spark plug, and what it means:
- Faulty Crankcase Ventilation. Clogs in the crankcase breather can cause oil to leak into your combustion chamber. You’ll know this is your problem if you’re also experiencing a decrease in your engine’s performance, such as slower acceleration.
- Faulty Intake Valve Seals. Valve seals help ensure your car’s fuel doesn’t mix with other liquids in your vehicle’s system (like oil). If the seals have worn out, the oil may leak through, damaging your spark plugs. Valve seal replacements can be an expensive repair.
- Faulty Pistons or Piston Rings. If your problem is with the engine’s piston or piston rings, you may be facing a hefty mechanic bill. Symptoms may include dark exhaust smoke and decreased engine performance.
No matter the issue, if you find oil on your spark plugs it’s a good idea to replace them to avoid further damage to your vehicle.
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