Oil on Spark Plug Threads – Causes and How to Fix

Oil is a vital part of an engine but it can also cause a lot of damage if it leaking from somewhere within the body. You should not ignore oily spark plug threads found during routine maintenance.

This article will discuss oil on spark plug threads and its causes. It also discusses how to fix it without having to do a routine checkup.

What causes oily spark plug threads?

1. Damaged Valve Cover 

The valve cover is a piece made of plastic that covers the intake valves. The intake valves let air in the combustion chamber for fuel injection. It is important to replace it if it’s broken or worn out as this could cause oil buildup on the spark plug.

2. Broken Piston Rings 

Broken Piston Rings 
Credits: TuningBlog

Piston rings seal off the top of the piston within the cylinder. The rings will wear over time and need to replaced. If the rings don’t fit correctly, the engine can leak oil or gas. 

3. Seals with leakage O-rings

Credits: Youtube

They are used for prevent oil leakage Seal and protect mechanical parts. These seals are not only waterproof, but also resistant to high temperatures, vibration, and pressure. The oil travels from the manifold to reach the spark plug threads. 

4. Improper Cleaning 

Incorrect cleaning can result in debris being left behind on the sparkplug. This debris can get stuck between the gap in the spark plug and cause the spark to not fire properly. 

5. Ignition System Issues 

An incorrect ignition timing can lead to excessive oil buildup at the spark plugs and cause problems with your engine. Also, excessive heat Spark plugs can become clogged with oil. If this happens, it can damage the engine. 

There are other factors that can affect the life of your spark plug

1. Old Spark Plugs 

Old spark plugs are no longer insulated and have lost their value. This exposes the metal shell, increasing its conductivity. This allows current to flow more easily through the shell, causing sparks. 

2. Water 

Water can get into the spark plug’s inner chamber and accumulate in the space between the firing (or center) electrode and ground electrode. This water can corrode and reduce the insulation of the sparkplug’s metal parts. Water, in and of itself, is bad. water in engine oil.

3. Poor Maintenance 

Dirt and grime can block the air filter and prevent clean air from getting into the engine. Dirt can also build up between the center electrode and the ground electrode. This reduces the voltage that reaches spark plug’s firing tips. Dirty spark plugs can result if you don’t change them enough. 

Spark Plugs: Signs of Oil 

Each year, inspect the spark plug of your vehicle. Repair or replace any layer of oil or carbon on your vehicle’s spark plugs. If you see these symptoms, it is time to replace or change your spark plugs. 

  • Bad gas mileage. 
  • Low oil pressure 
  • Your engine is experiencing performance problems. 
  • Excessive smoke is coming from the exhaust pipe. 
  • Without warning, your engine suddenly stops. 
  • Accelerating causes the engine to make a loud rumbling sound. 

After sitting inactive for a while, the engine will not start. 

If your car displays any of these symptoms, it is time to get it checked. To have your spark plug repaired or checked, schedule an appointment with your technician. Continue reading if your intention is to fix the spark plug yourself. 

What Are the Effects of Oil on Spark Plugs? 

  1. The engine can catch fire if the spark plug is not working while it runs. 
  2. It can reduce your vehicle’s range or fuel economy. 
  3. Oil buildup over time can cause engine parts to wear. 
  4. An oily spark plug can decrease the engine’s power. 

How do you remove oil from spark plug threads? 

You can fix your spark plug by yourself, or you just want your car to go a few extra miles to get to the mechanic.   

These are the three options available to you that will help you get oil out of your spark plug. 

1. Wire brush

wire brush cleaning spark plug

This is the easiest and quickest way to get rid of oil from spark plugs. You should wear gloves when you do this as oil can easily get in your hands.  


  1. Make sure you attach your spark plug to something. Use a stand, or a holder. 
  2. Use the brush to thoroughly rub the spark plug. Continue to rub the brush over the spark plug until it is clean and shiny. 
  3. Use a little alcohol to clean the threads. 
  4. Use a sealant, such as graphite or silicone to prevent oil buildup. 

2. Sandpaper


Sandpaper is an inexpensive way to get rid of oil from your spark plug.  


  1. Use alcohol or gasoline to clean the spark plug. 
  2. Use a brush to gently scrub the plug of carbon. 
  3. Use sandpaper to rub the spark plug. 
  4. Continue to clean the spark plug until it shines. 

3. Heat 

The removal of oil and carbon layers can be made easier by heating your spark plug to a particular temperature. Heat heats the oil from your spark plugs and melts it. Use gloves and a mask to protect yourself from any possible danger. It is important to not leave the plug on a high heat for too long as it can melt. 


  1. Place the plug and holder on top your gas stove. 
  2. It should be heated for 5-10 minutes over a low flame. 
  3. Let it cool completely before reinstalling. 

If none of the above methods work, you can watch this video to learn how to clean spark plugs.


How can you avoid oily spark plug threads 

1. Consistent service 

This is the best method to ensure your vehicle is in top condition. It is also a good idea to contact your mechanic about the problem. This will help prevent any further damage. Regular maintenance on your vehicle can prevent engine damage and poor performance from oil on the plug.  

2. Oil-Free Lubricants 

You must also ensure that you use lubricants without oils. The threads of spark plugs can be clogged by oil buildup. You can use a synthetic oil-based lubricant such as WD40, or a similar product. These products are made for extreme conditions and can be used to clean or lubricate any part that requires it. 

3. Spark Plugs of High Quality 

If your spark plugs are still having problems, it is worth replacing them. A quality spark plug will last a lot longer than a low-quality one, and it will provide many years of reliable service. 


Oil on your spark plug could adversely affect your engine’s performance or lifespan.  Regular servicing of your car is a must. It is also important to take steps to prevent oil buildup around the threads. To avoid any significant damage to your car, you should use high-quality sparkplugs.

FAQs about Oil on Spark Plugs

Is it normal to have oil on spark plug threads?

Oil on spark plugs is not normal. Oil-covered spark plugs can cause serious damage. If they get dirty, you may need to clean them before putting them back in the engine.

Can a bad PCV valve cause oil on spark plugs?

A bad PCV valve can cause oil on spark plugs. If the engine is running fine and suddenly stops working, check the PCV valve first. You may have a leaky valve causing oil to collect around the spark plug thread.

Can an oil leak cause a misfire?

An oil leak can cause a misfire. When an engine starts, the spark plugs are ignited. If they don’t ignite properly, then the engine won’t start. A leaking oil line could cause the spark plug not to fire.

Will oil on spark plugs cause the car not to start?

Oil on spark plugs causes carbon buildup inside the combustion chamber. Carbon buildup reduces the amount of oxygen reaching the engine’s cylinders. The spark plug will no longer fire properly if the oil is allowed to dry out. When the spark plug does not fire correctly, the engine will not start.

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