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Oil on the Spark Plug

By Joe Ballard
Published on August 14th, 2024

What are the warning signs?

Usually, when oil is on the spark plug due to oil finding its way into the combustion chamber, the symptoms will be noticeable. Even tiny amounts of oil seeping into the combustion chamber are enough to cause problems if left unchecked over time. The main reason is that the unburned oil collects on the spark plug electrode, interrupting the flow of electricity that causes the spark. This will almost always result in a misfire of that particular cylinder, resulting in a loss of power, rough idle, and a decrease in fuel efficiency. If you are a DIYer, you can use an OBD scanner to identify which cylinder has the misfire.

But wait, there's more. If the engine spark plugs are fouled, the engine could be more difficult to start and hesitate on acceleration, possibly resulting in long-term damage to the engine. Not only that but along with this damage, the vehicle's emissions could be impacted by increasing chemical byproducts that could harm the environment and even clog up the catalytic converter.

The earlier that oil-fouled spark plugs are identified, the better the odds are that you can make a repair before serious damage is done to the engine. If you have a CEL on and detect a misfire, then connecting your OBD scanner to see if any codes are present makes sense. Codes that begin with P030(x) are common when there are one or more fouled spark plugs. You can also quickly check the engine coolant to see if there are signs of oil in it, as this could indicate that a head gasket is leaking oil into the combustion chamber.

Key Takeaways

Spark plugs with oil on them can be cleaned to remove the oil or replaced if they have reached their time limit or miles based on the manufacturer's recommendation in the owner's manual. With that said, there is a reason that they have been fouled, and that must be addressed by finding the root cause of the problem. To do this, you can perform several tests to determine where the problem is; these include:

• A leak-down test will indicate if the valve seals, head gasket, or cylinder walls are at fault.
• A compression test is helpful to determine if the piston rings are the cause of the problem.
• Look at changing the PCV valve. If it is stuck or clogged, it could push oil into the combustion chamber via the intake manifold.
• Make sure that you are using the correct oil grade for your engine. Using the wrong grade, especially on older engines, could allow some oil to bypass the piston rings.

Remember that the key to preventing oil on spark plugs is prevention via regular maintenance. Regular oil changes to keep your engine lubricated will minimize the potential for oil to bypass the piston rings and ensure that the other potential problem areas will not cause problems in the future. It is also important to note that the simple act of maintaining the proper oil level (not overfilling) will keep internal pressure in the engine from getting elevated.

Conclusion

If you notice any of the warning signs of oil on the spark plug, then there is a problem somewhere in the engine. It is important to identify the problem and have it repaired as soon as possible to avoid serious damage to the engine. These warning signs include, but are not limited to, white smoke or a gasoline smell coming from the exhaust, decreased performance, decreased fuel economy, or a CEL from an engine misfire.

By performing regular maintenance, you can keep your engine in good working order and significantly reduce the chances of encountering serious issues like head gasket failure, piston failure, or valve issues. Just the simple act of changing your oil on a regular basis will reduce friction and heat and reduce stress on many engine components that could cause oil to leak into the combustion chamber and foul the spark plugs. You may also want to consider driving less aggressively, as hard acceleration puts a lot of stress on internal engine components.

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