A spark plug is in charge of providing the initial spark needed to ignite the air-fuel mixture inside the combustion engine. If your spark plug becomes coated with oil, it can have severe consequences on your engine. A faulty spark plug has a direct impact on the power output of your engine and can cause your engine to misfire more frequently. 

In this post, we will look at some of the reasons for oil accumulating around your spark plug and various methods for eliminating the oil coating. We’ve already written a detailed article about oil in spark plug threads. Check it out if you want.

What happens when Oil Fouled a Spark Plug? 

A spark plug is required to generate an electric spark in your combustion engine. No amount of oil should be present on spark plugs since oil-fouled spark plugs can cause extensive damage to your engine components. 

Oil-fouled spark plugs can lead to frequent vehicle stalls, bad fuel economy, degraded engine performance, and many more. Any type of fluid around your spark plug does not necessarily indicate that the engine oil fouls it. Let’s see how you can indicate that your spark plug is affected by oil.

How to Indicate Oil-Fouled Spark Plug? 

If you notice a brown grayish coating on the sides of the spark plug electrode, this could indicate that your engine is running normally and there is no oil deposit surrounding the spark plug. Although all fouled spark plugs are easy to determine, the oil-fouled spark plugs have different colors. Here’s a quick video in case you’re lazy to read the text.

You need to be more concerned if you discover a light brown deposit around the spark plug’s electrode. This could indicate oil leaking into your engine and damaging the spark plug. 

A black and dried layer surrounding the threads of a spark plug could be a layer of carbon impurity from the combustion chamber. Carbon coating occurs when your engine has an incorrect air/fuel mixture, which can foul the spark plug. 

Let’s look at some of the symptoms that may help you decide whether you have a faulty spark plug or not. 

Symptoms of an Oil Fouled spark plug- 

  • More frequent engine misfires. Misfire happens when the engine cylinders do not provide enough power to start the engine. 
  • Your engine’s acceleration or power has been lowered. 
  • The engine light is flashing more frequently. 
  • It can cause a banging sound in your engine if the fuel-air combination is not burned properly. 
  • Oil fouled spark plugs can lead to more rough idling in your engine, resulting in frequent vibrations and shaking throughout the vehicle. 
  • It may result in increased oil usage. You may also notice black fumes from the engine exhaust due to an unburned air/fuel mixture. 

What Causes an Oil Fouled Spark Plug? 

The spark plug is located inside the engine head, and the spark plug’s electrode is in direct contact with the combustion engine. If oil is released into the combustion engine for whatever reason, oil can collect around the spark plug, leading it to fail. 

Let’s look at some of the reasons oil is getting into your spark plug. 

Rich Air Fuel Mixture 

The primary cause of the oil film forming around the spark plug is an incorrect air-fuel ratio. When the ratio is improper, most unburned fuel/oxygen creates pressure around the engine components. This caused oil to flow into the spark plug, causing it to fail. Sometimes, this even causes the oil to smell like gas.

Carburetors are in charge of maintaining the air-fuel ratio in your combustion engine. Oil fouled spark plug is more common with straight-through carburetors since the air is drawn directly from the atmosphere via a venturi. This increases the air inside your cylinder, resulting in oil leaks. Manufacturers recommend that the fuel ratio be “stoichiometric” (14.7:1), which is the optimal fuel ratio with no unburned fuel or oxygen remaining.

Damaged Valve Guide Seals 

Valves are directly responsible for the operation of the lubrication process and the consumption of oil. If the valve seal is damaged, oil can enter the combustion chamber via the valve steam. Oil will develop a film surrounding the spark plug inside the combustion chamber, leading it to fail. 

Valve seals are frequently broken when the valve clearance between the valve and the valve guide is improper. This can result in greater operating temperatures and worn-out valve seals. 

Damaged Piston Rings

Broken Piston Rings 

Piston rings are in charge of transferring heat throughout the engine. If the piston ring wears down, oil can enter the spark plug and cause it to misfire. 

Piston rings are frequently worn out due to the oil film that forms on the cylinder wall during combustion. This causes friction inside the piston ring, which leads to piston ring wear and tear. Damaged or old piston rings can also go inside the intake manifold, which you probably want to avoid.

Damaged Head Gasket

Damaged Head Gasket
Credits: Youtube

Under severe temperatures, the head gasket might fail, allowing oil to leak through engine components. The head gasket is in charge of sealing the fuel chamber so that coolant or oil does not seep into any other engine component. It is also responsible for maintaining sufficient pressure inside the combustion engine to operate the engine. 

Coolants can leak into the combustion chamber when the head gasket wears down. Oil from the combustion chamber can readily accumulate around spark plugs, leading them to fail. 

How to Clean Oil Fouled Spark Plug

If your spark plug is not severely damaged by oil and is in good condition, you can clean it using some simple ways. Here are some steps for cleaning your spark plug.

  1. Take the spark plug out of the engine head.
  2. Holding it with mole grips, heat it with a blow torch. Make certain that any sticky carbon and oil deposits surrounding your spark plug are melted.
  3. Scrap the accumulated oil and carbon surrounding the spark plug electrode with a sharp object such as a knife or screwdriver.
  4. Apply a cleaning spray on the top of the spark plug around the ceramic.
  5. Use a wire brush or toothbrush to clean it thoroughly.
  6. Repeat until no oil coating remains on the spark plug and it appears shiny and clean.

How to Avoid Oil Fouled Spark Plugs 

  • Replacing worn engine components such as piston rings, valve seals, and head gaskets to prevent future oil leaks. 
  • You should change your engine oil regularly. It was usually recommended to change the oil of old engines every 3000-4000 miles. But now, modern engine oils can run around 7000-8000 miles before replacement.
  • Maintaining the proper air-to-fuel ratio inside the combustion chamber. Oxygen level and pressure should be checked regularly to minimize excess air pressure. 


To summarize, keeping the spark plug in good condition is important. This is because it is important for providing power and spark to your engine. To avoid oil leaks, we must change our engine oil regularly. If you observe any wear and tear in engine components, have them serviced by your mechanic. 

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