Oil Fouled Spark Plug – Causes & How to Fix

Spark plugs are responsible for providing the initial spark necessary to ignite the air-fuel mixture within the combustion engine. Oil can cause severe damage to your engine’s spark plug. A faulty sparkplug can have a direct effect on your engine’s power output and may cause your engine to misfire frequently. 

This post will discuss the reasons oil can build up around your spark plug as well as the different methods to get rid of it. We have already written a detailed article on this topic. oil in spark plug threads. It is available for you to view if you wish.

What happens when oil is poured on a spark plug? 

To generate an electric spark in your combustion engines, a spark plug must be used. Spark plugs shouldn’t contain oil as they can cause damage to engine components. 

An oil-fouling spark plug can cause frequent vehicle stalls, poor fuel economy, reduced engine performance, and other problems. However, a fluid around your sparkplug does not necessarily mean that it is clogged with engine oil. Let’s look at how to indicate that your sparkplug is oiled.

How to identify oil-fouled sparkplug? 

A brownish-grayish coating around the spark plug electrode could be an indication that the engine is operating normally and there is not oil in the vicinity. All fouled sparkplugs are easy to identify, but oil-fouled ones have different colors. For those who are too lazy or unable to read, here’s a video.


If you notice a dark brownish deposit near the spark plug’s electrode, this is a sign that your engine may be suffering from oil leaking into it. This could indicate that oil has gotten into your engine and is causing damage to your spark plug. 

Carbon impurities from the combustion chamber could cause a dried and black layer to form around the threads of the spark plug. The carbon coating can occur when the engine is using an incorrect mixture of air and fuel. This could cause spark plug to become clogged. 

Let’s examine some symptoms that can help you to determine whether your spark plug is faulty. 

Oil Fouled Spark plug Symptoms 

  • More frequent engine misfires. When the engine cylinders are not powerful enough to start the engine, misfires can occur. 
  • The engine’s acceleration and power have been reduced. 
  • The engine light is flashing More often. 
  • If the fuel-air mixture is not properly burned, it can make your engine bang. 
  • Oil-fogged spark plugs can cause more rough idling, which can result in vibrations and shaking throughout your vehicle. 
  • It could cause increased oil use. Unburned fuel/air mixtures can also cause black smoke from the engine. 

What is the Cause of an Oil Fouled Spark Plug 

The sparkplug is located within the engine head. Its electrode is directly in contact with the combustion engine. Oil can build up around the spark plug and cause it to fail if oil is accidentally released into the combustion engine. 

Let’s take a look at the reasons oil gets into your spark plug. 

Rich Air Fuel Mixture 

An incorrect air-fuel mixture is the main reason for the oil film around the spark plug. The incorrect ratio of fuel/oxygen can cause pressure to build up around engine components. This caused oil to seep into the spark plug and led to it failing. This can sometimes even cause the oil to smell like gas.

Carburetors maintain the combustion engine’s air-fuel ratio. Straight-through carburetors are more likely to have an oil fouled spark plug because the air is pulled directly from the atmosphere via the venturi. This can lead to oil leakage and increases the volume of air in your cylinder. Manufacturers recommend that you fuel ratio be “stoichiometric” (14.7 to 1), which is the optimal fuel combination with no unburned gasoline or oxygen.

Damaged Valve Seal Guide Seals 

Valves directly control the operation of the oil lubrication process. Oil can get into the combustion chamber through the valve steam if the seal is broken. The combustion chamber can be damaged if oil builds up around the spark plug, causing it to fail. 

When the clearance between the valve and guide is not correct, valve seals can be damaged. This can lead to higher operating temperatures and worn-out seals. 

Piston Rings Damaged

Broken Piston Rings 

The piston rings transfer heat through the engine. When the piston rings wear down, oil can seep into the spark plug causing it to misfire. 

The oil film that forms on the wall of the piston cylinder during combustion causes the oil to clog the rings. This causes friction in the piston ring and can lead to piston ring wear. Also, damaged or worn-out piston rings can lead to damage. inside the intake manifoldYou probably want to avoid.

Head Gasket Broken

Damaged Head Gasket
Credits: Youtube

Extreme temperatures can cause the head gasket Oil could leak from engine parts if the head gasket fails. The head gasket seals the fuel chamber to prevent coolant or oil from seeping into other components. It maintains enough pressure in the combustion engine for the engine’s operation. 

When the head gasket wears, coolants can leach into the combustion chamber. The combustion chamber may allow oil to build up around the spark plugs and cause them to fail. 

How to Clean Oil Fouled Plugs

You can clean your spark plug if it isn’t damaged by oil or is otherwise in good condition. Here are some ways to clean your sparkplug.

  1. Remove the spark plug from the engine head.
  2. You can heat the spark plug by holding it in your hands with molegrips. Make sure that all sticky carbon and oil deposits around your spark plug have been removed.
  3. Use a sharp object like a knife or screwdriver to remove any oil and carbon accumulated around the spark plug electrode.
  4. Spray a cleaning solution on the top of your spark plug to clean the ceramic.
  5. To clean it well, use a toothbrush or wire brush.
  6. Keep going until the spark plug appears clean and shiny.

How to Avoid Oil Foulled Spark Plugs 

  • Replace worn engine components, such as piston rings and valve seals, to prevent oil leakage. 
  • Your engine oil should be changed regularly. Old engines were recommended to be changed every 3000-4000 miles. Modern engine oils can be used for approximately 7000 to 8000 miles before they need to be changed.
  • It is important to maintain the correct air-to-fuel ratio in the combustion chamber. To reduce excess pressure and oxygen levels, it is important to regularly check the pressure and oxygen level. 


It is crucial to keep the spark plug in good shape. This is because the spark plug is responsible for providing power and spark to your engines. We must change our engine oil frequently to avoid oil leaks. You should have your mechanic service engine parts if you notice any wear. 

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