Why Is There Oil On My Spark Plugs - T-Tees - Your Answers Await, Life's Questions Unraveled

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Causes of Oil on Spark Plugs

Oil doesn’t burn nearly as well as gasoline or the oxygen in the air that’s drawn into the engine. And when it gets on the spark plugs, it’s a condition known as oil-fouled spark plugs, since they don’t operate as well as they should. It can be caused by a handful of conditions such as:

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Worn valve guides or intake valve seals
Worn-out or broken piston rings
A blown head gasket
Clogged crankcase ventilation system
Leaking valve cover gasket
Overfilled engine oil

Effects of Oil on Spark Plugs

When you have oil on spark plugs, symptoms will be noticeable. When one of these issues is present, oil finds its way into the combustion chamber, often in tiny amounts at a time. But the unburned oil particles collect on the spark plug, interrupting the flow of electricity between the electrodes. The result is a misfire in that particular cylinder, which causes a loss of power rough idle, and decreased fuel efficiency.

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But that’s not the only effect. With fouled spark plugs, the engine could be more difficult to start, it can hesitate on acceleration, and potentially cause long-term damage to the engine.

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Along with the effects on the vehicle, emissions are affected. Oil on spark plugs can produce increased chemical byproducts that can be harmful to the environment, as ell as clog or damage a catalytic converter.

Diagnosis and Detection of Oil on Spark Plugs

The earlier oil-fouled spark plugs are detected, the better the odds of a repair before serious damage occurs. The most obvious step to diagnose oil on spark plugs is to remove each of them and check for the presence of wet oil or a black, tar-like buildup on the electrodes, insulator, and threads.

However, some preliminary checks can also begin to point you in the right direction. Check the engine oil level to see if it’s lower than it should be, particularly if you’ve recently changed the oil. If so, it could indicate that there’s an oil consumption issue. A Check Engine Light with DTCs related to a misfire – codes beginning with P030[X] – are quite common when there’s one or more oil-fouled spark plugs.

Addressing the Issue: Solutions and Preventive Measures

Spark plugs can often be cleaned to remove oil and residue that contaminate them. However, replacing the spark plugs is a good idea if they’re getting on in age and mileage already. But there’s a reason that oil has fouled them, and that must be addressed.

Identify the root cause of the problem and fix it. A leak-down test can indicate if the valve seals, head gasket, or cylinder walls are to blame, and a compression test is helpful to determine if the piston rings are the root.
Change the PCV valve. If the PCV valve is stuck, oil could be pushed into the combustion chamber through the intake. It’s an easy repair.
Use the correct oil grade. Especially on high-mileage engines, using the wrong grade of oil could allow some to bypass the piston rings.

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Prevention is a much more cost-effective method than a repair in this situation, and routine maintenance is the best way to keep oil-fouled plugs at bay. Regular oil changes keep your engine well lubricated, minimizing the potential for oil to push past piston rings. Avoid overfilling the engine oil to keep internal pressure from getting elevated.

And if you find you need new spark plugs or other parts to correct oil consumption issues, AutoZone is your trusted source. With friendly staff and a huge assortment of parts for most makes and models, you’ll find everything you need right here. If the job is too big for you, seek out one of our Preferred Shops to help you do the job.