Oil On Spark Plugs: 7 Common Causes & Fixes (Is It Normal?)

By August 31, 2022Common Questions

Oil on spark plugs is common in cars but it could be damaging. Common causes include leaking valve cover gaskets, bad piston rings, faulty O-ring seals, or bad pistons. 


To fix oily spark plugs, you need to fix the root cause. Replacing the spark plugs alone is not enough.

Personally, I have experienced oil on my spark plugs with my Honda Civic. It was due to a leaking valve cover gasket. I noticed my engine performance dropped significantly. I also experience engine misfire and difficulty in starting my car. 

In this article, we will show you signs of an engine with faulty spark plugs and what to do when you notice them.  

7 Common Causes Of Oily Spark Plugs

1. Leaking Valve Cover Gasket

Valve Cover Gasket

The valve cover gasket  when damaged could cause oil to escape from the engine into the spark plugs and make them oily. 

A leaking valve gasket cover is one of the most common causes of oil on spark plugs. The valve gasket cover is an important part of the engine. It protects the cylinder head parts from contamination and prevents oil from leaking to other parts of the engine that it is not wanted. 

Once the valve cover gasket is damaged it leaves the cylinder head and major parts of the engine at the mercy of the harsh weather condition. It will also cause oil to spill without control. The oil leakage from the damaged valve cover then finds its way to the spark plugs. 

When you check the engine plug and notice that the oil on it is not coming from within the engine, it is most likely from the leaking valve cover. 


2. Bad Piston Rings

Piston Rings

The piston rings are located in the combustion chamber, around every piston in the engine. If they are damaged, oil can escape from the piston and spill to other parts of the engine including the spark plug and make them oily. 

Piston rings are meant to apply accurate pressure, ensuring that oil moves across the cylinder surfaces while working. The piston rings keep oil from escaping into the combustion area. If this happens, it could reduce the engine performance. 

If the piston rings of your vehicle get bad or worn out, it will be unable to stop oil leaking. With this happening, oil can easily get to the spark plugs and stop oil from reaching the moving hardware.

Once you notice your engine’s poor performance, check the piston ring.

3. Faulty O-Ring Seal

O Ring Seal

As the name implies, the O-ring seals the spark plugs properly. If the rings are damaged then oil from the engine can contaminate the spark plugs and make them oily. 

The rings seal the spark plug, keeping oil from going to a particular part of the spark plug. If the O-ring seals is tampered with, then there is nothing protecting the spark plug from oil and other elements that could damage it.

A way to know if the ring seal is damaged is if you can not find oil on all the spark plugs. In this case, the spark plugs with oil on them have damaged the O-ring seal.


4. Obstructed Crankcase Ventilation

Crankcase Ventilation

An obstructed crankcase ventilation will cause oil to spill into the combustion chamber which would then find its way to the spark plugs and make them oily. 

The crankcase ventilation problem is a more serious one because the crankcase ventilation system is located in the combustion engine. The crankcase ventilation serves as a means of removing excess or unneeded gases from the crankcase of the internal combustion system. 

When the crankcase case ventilation gets obstructed, more pressure is built up. It then causes oil to be forced into the combustion chamber. Oil can then get to the plug from the engine’s combustion area. 

Ensure you fix the problem after it is noticed to avoid further damage.


5. Bad Pistons


Damaged engine piston will allow oil to escape into the engine combustion due to cracks and holes in the piston and cause oily spark plugs. 

The engine piston is a major part of engine combustion. The hardware converts the engine from the combustion process and turns it into a mechanical push. 

Pistons in the engine can be subject to wear because it is working continuously at a very high speed. Once there is wear, it could open or crack in the piston letting oil escape to the spark plugs. 

The bad piston could cost a lot to fix, but it is not a problem that can be managed or ignored. Your engine could be destroyed, which would cost even more to replace or fix.


6. Faulty Intake Valve Seal

Intake Valve Seal

When the intake valve seal gets damaged, it will allow air, fuel and oil to mix, which should not be done. The oil can easily get the spark plug when this happens. As a result of the mixture, the combustion system and exhaust outflow will be contaminated, leading to blue smoke.


7. Damaged Spark Plug Tubes

Spark Plug Tube

The spark plug is prone to crack open during the extreme working condition of the vehicle’s engine. The crack in the tube causes oil to escape into the spark plugs and make them oily.

Although this cause of oil on the spark plug is not as common as the above causes, it is common with some vehicles. Some vehicles are equipped with a 3.6L 6V engine. The solution to this issue is to replace the total cylinder head completely.

What Happens if I Have Oil in My Spark Plugs?

Oily Spark Plugs

Having oil on your vehicle’s spark plugs is not normal and could cause damages like weak ignition, engine misfire, increased fuel consumption and weak acceleration.

Many people take a look at their spark plugs and see oil contamination, they do not know that this contamination could be harmful to the vehicle’s working condition.

As we know, the spark plug serves the purpose of creating sparks that result in the ignition of the engine. An oily spark plug can prevent this from happening or make it difficult. 

When your vehicle has a problem with the ignition, it could result in an engine misfire. The misfire happens because the combustion system is not working, and the cylinders remain idle. All of this is due to oily spark plugs.

Another serious problem that an oily spark plug could cause is increased fuel consumption. With a spark plug underperforming due to contamination, the engine will have to find a way to meet its needs.

Thus, there will be increased fuel going into the cylinder. The increased fuel helps maintain the pressure in the combustion chamber. With this happening, the fuel consumption of your vehicle worsens. 

Other effects of oily spark plugs may include:

  1. Trouble starting the vehicle
  2. Engine being loud 
  3. Check engine light 
  4. The vehicle struggles to accelerate 
  5. Blue exhaust smoke

Once you notice these signs, check your spark plug for oil contamination or any contamination. 

Furthermore, oily spark plugs are an indication of something being wrong with your vehicle. So when you notice oil on your spark plug, it is time to do proper checks and servicing of your vehicle’s engine. 

Can I Drive With Oil in My Spark Plugs?

You can drive a car with oil spark plugs, but it is not advisable. Using spark plugs contaminated with oil could cause a lot of damage to your engine. 

Once you notice oil on your spark plugs, getting new sets for your engine would be better. You can lose your engine to overheating or fire with bad spark plugs. You must always check your spark plugs to avoid causality like fire. 

Sparks plugs with oil have become a common occurrence that many vehicle owners are ignoring. To better understand the contamination, you must know the causes of oil on spark plugs. 

What Do I Do if I Have Oil on My Spark Plugs?

When you have oily spark plugs, you need to find the source of the oil leak and fix it. Once the leak is fixed, you should replace the spark plugs instead of repairing them.

You can often tell where the leak is coming from by just determining when the oil contamination is on your spark plug. 

If the oil contamination is found on the plug’s well, this means that there is a part of the engine that is leaking oil. It could be components in the engine, like the O-rings,  found around the well or valve cover gasket. 

Also, if you are worried about the oil residue in the plug well after fixing these components, you do not need to be. After some time, the oil residue burns off. You can also spray carb cleaner into the spark plug well and allow the oil to flow down into the combustion area. 

However, if the oil contamination is found on the tip of the plug, or the plug’s tip looks ashy, then it is a more serious problem. Oil contamination found in these areas can be related to engine problems.

It means that oil has found its way into the combustion system, this could be due to a bad piston ring, bad piston, faulty intake valve, etc.

How Do I Fix Oily Spark Plugs?

When you notice oil on your spark plug, you will have to fix the cause of the oil leak. If the cause of the oil leak remains, then your spark plugs will keep getting contaminated by oil. 

To fix contaminated spark plugs, you must take them out using a ratchet wrench and spark plug socket. After taking them out, proceed to clean them using a rag. Cleaning with a rag will help you remove the oil and other debris forms. Then spray with a brake cleaner. Leave the brake cleaner on it for about 10 to 15 minutes. 

Once the spark plug has sat for 10 to15 minutes, use a wired brush to remove all other contamination from the plug. Use compressed air to remove dirt during the cleaning process. Compressed air prevents any form of liquid from getting into the plug. 

After properly cleaning, you will need to gap the spark plug. You may use a plug gauge to do this process. You can refer to your vehicle’s manual for accuracy if you do not know how to gap your spark plug. 

After the gapping has been done, you can now reinstall the plug spark into the engine. Before doing this, you ensure your plug well is clean. You can spray carb cleaner into the well and allow the oil residue to flow into the combustion system. 

Also, ensure the spark plug’s thread is clean before reinstalling the plug. 

How Do I Know If I Need New Spark Plugs?

You need new spark plugs when your car starts having poor ignition, reduced engine performance or poor oil consumption. 

The spark plugs help with the ignition process of the vehicle, and once this ignition process does not go on as it should, it could be a plug problem. It may be an indication that you need to change your spark plugs.

Generally, many engines’ poor performance is often caused by a bad spark plug. You may need a new spark plug when your engine does not generate the power it used to generate. Also, your engine may be sluggish in picking up acceleration,  a sign you need a new spark plug. 

In addition, manufacturers suggest that you change your spark every 100,000 miles. It does not necessarily mean the plug will go bad after 100,000 miles of usage. It is just advisable to change it after that period. 

The durability of a spark plug depends on many factors. One major factor is the condition of your engine. If you have a spark plug that is always going bad, your engine may have some issues. 

Changing your spark plug  comes with some good benefits. Here are 4 benefits when replacing new spark plugs.

1. Healthy working combustion system

The combustion system relies on the spark plug for ignition. If the spark plug is bad, the combustion system may not function as it should. Changing your spark plug allows the plug to fully assist the combustion system in carrying out its role. 

2. Better fuel economy

As we have mentioned initially, a bad plug can cause an increase in fuel consumption. With a new spark plug functioning properly, the engine does not need more fuel in the combustion system. The engine will now consume fuel as it is supposed to. 

3. Better exhaust emission

A properly maintained vehicle in which the spark plug is changed regularly will produce good exhaust emissions. 

4. Better engine starts

You can expect a better and less embarrassing start with a new spark plug. Ignition will be done perfectly without having to do it over and over again.    

Good Spark Plugs vs Bad

Good Spark Plug  Bad Spark Plug
Ignition  Powerful Weak
Fuel consumption  Efficient Poor
Exhaust emission  Low High
Oil consumption Efficient  Poor
Check engine light No Yes
Engine sound Low Loud


There is a huge difference between using a good spark plug and using a bad one. You can majorly see this in the performance of your engine. Engine underperformance is one major feature of a bad spark plug.

The engine begins to underperform when the spark cannot produce the spark needed to cause the ignition that the combustion system needs. However, with a good spark plug, the proper spark is needed for the combustion system to work properly. 

Also, bad spark plugs do not have a good start compared to the good spark plug. You will experience a more prolonged, embarrassing start with a bad spark plug. On the other hand, a good spark plug has a better and quicker start. There will be no need to keep trying the ignition. 

You can also expect a bad vibration and rough sound from your engine with a bad plug. You can also hear a knocking sound coming from the engine when accelerating. The reason for the sound is that the spark plug fails to ignite the fuel properly. You can avoid embarrassing sounds if you regularly change your engine’s spark plug. 

Furthermore, a bad spark plug can trigger a check engine light. The spark plug plays a significant role in the smooth running of the engine, and if it is not doing its job, the Powertrain Control Module (PCM) can easily notice it and trigger the check engine light.

Having a good spark plug will not trigger a check engine light. It is because it serves its purpose to the engine properly, and the PCM can not pick up any problem. 

If your car is consuming too much fuel, it could result from a bad spark plug. The engine will require more fuel to cause ignition with a bad spark plug. It is why you need to change your spark plug. It will bring down your cost of fuel. 

Finally, you can expect a bad exhaust emission from a spark plug. One of the major features of a bad spark plug is blue exhaust smoke. It is not the same with a good spark plug. You can expect a better emission from a good spark plug.

Cost To Replace Spark Plugs

Spark plugs can cost as little as $15 to a whopping $200 and even more. Although, the cost to replace a spark plug varies due to many factors. Some of these factors may include the type of plugs your vehicle uses or the number of cylinders your vehicles use.

Many people are made to believe that spark plugs are the same with each brand which is not through. Most sparks are made with different materials, which determines their price.

There are copper spark plugs, single platinum spark plugs, double platinum spark plugs, and iridium spark plugs. These different plugs do not cost the same, and the iridium spark plug may be more expensive. 

The iridium spark plug is considered more expensive because it is the best. It can last up to 25 per cent longer than platinum spark plugs. You must get the specified spark plug for your vehicle when buying a spark plug. To do so, you can refer to the manual of your vehicle. 


Q: Is It Normal for Spark Plugs to Have Oil on Them?

A: It is not normal to have oil on your spark plug, which shows an underlying issue with an engine or a component leaking. Oil on a spark plug can be caused by many factors, such as leaking valve cover gasket, faulty piston, and faulty air intake. 

It is important that once the source of the leak has been identified, you must replace or fix the problem immediately. 


Q: Can a Misfire Cause Oil on Spark Plugs?

A: The oil can cause the engine to misfire on a spark plug. It is because the spark plug cannot ignite the mixture of air and fuel in the combustion. In this case, combustion can not happen, leading to a misfire in the engine system. 

However, an engine misfire, if it happens regularly, could cause problems for the engine. Even though you can drive with an engine misfire, you are liable to have an accident if the engine is not repaired.


Q: Will Oil on My Spark Plugs Cause Cars Not to Start?

A: A spark plug contaminated by oil can cause your car not to start. The spark plug is the source of ignition of the engine, and once it is faulty, the car may either find it difficult to start or may not start at all.  


Q: Is It Cheaper to Change Your Own Spark Plugs?

A: The price to change a spark plug can be influenced by many factors. Some factors may include the quality of the spark plug, the type of spark plug used by your car and many more.

However, it is cheaper to buy and install a spark plug yourself. By doing it yourself, you can make safe money given to professionals. You will be saving about $100 if you do it yourself.


You must have the right knowledge about the right spark plug that will work for your vehicle. You can consult your vehicle’s manual.

Q: How Long Does Changing Spark Plugs Take?

A: Changing a spark plug will take an hour to change a four-cylinder engine. Also, the time can be influenced by the number of cylinders your engine has and the tools you will use to change the spark plug. 

Ifandi L.

Ifandi L.

Passionate about everything mechanical. Ifandi has been involved with motorcycles and cars since the old days - in his family's auto parts shop. Want to keep in touch? Scream "STRAIGHT PIPEEEEE" at the top of your lungs and Ifandi will show up.

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