Oil on Spark Plug Threads (Causes & Solutions)

Are you carrying out the daily maintenance activity on your car, and you mistakenly pull out your spark plugs only to discover that its threads are soaked with engine oil, and you are scared of what you saw?

There is every reason to be afraid because spark plugs shouldn’t have oil on them, let alone be soaked with oil.

Therefore, suppose you discover oil on your plugs, know that all is not well with several other parts of your engine.

This article will cover the different problems that can cause oil on your spark plugs, let you know the issues they would generate in your entire engine, and tell you how to address the problems.

We briefly explain them in detail below.

6 Reasons for Oil on Spark Plug Threads

Reasons for Oil on Spark Plug Threads

For every effect, there is a cause, and before addressing the issues that come with oil on spark plug threads, you have to understand why it occurs to highlight the root cause.

We’ve highlighted at least six significant reasons for oil on spark plug threads below;

1. Leaking or Worn Valve Guides

Let’s start with a leaking or worn valve, one of the most prevalent causes of oil on spark plug threads. Spark plugs in modern-day cars are often located around the intake valves and exhaust regions.

The intake valve controls how air is brought into the combustion chamber. If these valve guides get worn, they begin to leak, causing free oil leakage that will affect the spark plugs since they are situated near the valves.

2. Broken Piston

When a piston experiences a crack or is broken, it could cause oil to soak the spark plugs. Also, since the engine generates so much heat when it runs, it sometimes makes the piston heat up excessively, causing cracks.

The cracks cause oils to leak to the combustion chamber and the spark plugs. In other words, whenever piston rings are damaged, it is likely that oil has leaked into the combustion chamber.

If the piston is cracked or broken, you will notice a loss of power and a misfiring engine when the car is in operation, and you could also hear a rattling or knocking sound.

Driving your car when the piston is overheated and broken could result in severe damage to the engine, especially when you fail to address the problem at the right time.

In addition, any delay in replacing it could make you spend more on a subsequent repair.

3. Leaking O-Ring Seal

You will find the O-ring seal somewhere around the lower area of the spark plug wells, and its role is to prevent oil from coming in contact with the spark plugs.

So, once it is damaged, it won’t be able to function properly, and oil will be allowed free passage via the valves and into the spark plugs.

Engine misfiring is the most prominent symptom that points to leaking O-ring seals as the cause of oil on spark plug threads.

The O-ring seals are very affordable and easily replaceable; therefore, always remember to check them during your regular maintenance and change them promptly if necessary to prevent further costly engine repairs.

4. Bad Piston Rings

Bad Piston Rings

Another cause of oil on spark plug threads is are bad piston rings. A piston ring is a metallic split ring connected to the outer diameter of a piston.

Modern cars currently come with engines that feature three pistons for each cylinder.

The top two compression rings help seal the combustion chamber, whereas the bottom ring, called the oil control ring, manages everything that has to do with the supply of oil to the cylinder wall to help lubricate the piston skirt and the oil control rings.

It also helps to get rid of too much oil that touches the cylinder walls to prevent remnants that will enter the combustion chamber.

However, once these piston rings stop functioning well, it will cause oil to leak to the combustion chamber, thereby unavoidably leaking oil into the spark plugs.

5. Leaking Valve Cover Gasket

The valve cover gasket is also located on the cylinder head near the spark plugs. Its role is to protect the engine oil and prevent it from getting past the cylinder head.

However, once the valve cover gasket stops functioning well, it can cause oil to leak and touch the sparks plugs.

It is not unusual for the valve cover gasket to become damaged, as it is exposed to high engine temperature; and is susceptible to wear and tear.

Therefore, you should not fail to constantly check up on it and replace it if necessary to avoid any potential oil contact on the spark plug threads that might result in permanent damage to the engine.

6. Blown Head Gasket

A blown head gasket is also a cause of oil on spark plug threads. The head gasket is located somewhere between the engine block and the cylinder head. It serves as a seal between the two components.

The head gasket helps to provide a seal in the internal combustion chamber while also preventing coolant and oil from mixing up because the two fluids pass from the engine block to the cylinder head.

If the head gasket gets blown, it will allow oil to leak to the combustion chamber and spark plugs.

A blown gasket has several symptoms, such as, such as milky white oil, white smoke from the exhaust pipe, coolant leaking outside the engine from underneath the exhaust manifold, and overheating engine caused by the absence of coolant from leaks, or bubbles in the radiator or coolant overflow tank.

A blown gasket must be replaced right away. It is not advisable to drive your car with a blown head gasket, as it can only result in severe damage to the engine.

Also Read: Spark Plug Replacement Cost

How to Fix Oil on Spark Plug Threads

How to Fix Oil on Spark Plug Threads

We have highlighted and explained the various reasons why you might find oil on spark plug threads. Therefore, if you want to address the issue, here are some tools and materials you need

  1. Valve cover gasket and O-ring spark plug tube seal
  2. Power Handle
  3. Spray cleaner (for oil)
  4. Pliers
  5. Socket and spark plug socket
  6. Ratchet and extension
  7. Engine sealer
  8. Screwdriver

Oil on Spark Plug Threads: Step-By-Step Remedy

The next thing we’d be doing is to examine the possible causes below to enable us to discover why there is an oil leak that touches the spark plugs as a result.

First, you must turn off your vehicle and disconnect your car battery terminals to enable the engine to power off and stop supplying power.

Step 1: Remove Valve Cover & Examine the Head Gasket

The head gasket is a tiny component of the engine; hence is an elastic band designed to seal. To properly inspect the head gasket, you have to detach the valve cover using a screwdriver.

After doing that, you can now see the spark plugs and the tubes. The seals and gaskets will be visible to you also. Then, check for any crack or other possible damage.

If your assessment tells you the cause of oil on the spark plug threads is from the head gasket, then there’s a need for an immediate replacement.

Step 2: Remove the Spark Plugs

Spark plugs are designed to be inside the valve cover. So, if you must replace them, you have first to take out the valve cover.

But before doing that, you will have to remove the spark plug tubes and place them on the side.

After that, you can now remove the clamps from the hoses connected to the valve cover with pliers that can easily unlock them. Then, take out the hose with your hands.

The next thing is to get rid of the wiring harness from the top of the valve cover.

Once that is done, you can use a big socket and power handle to remove the nuts from the valve cover. While doing it, make sure it is removed one at a time with the tools unless it is easy to pry them loose with your hands.

You can now use a screwdriver to pry underneath the valve cover since it is always stuck on.

You can easily remove it just with mere wiggling and prying. If you have succeeded in removing the valve cover, you can now remove the seal found within each of the spark plugs.

Some car owners ignore the fact that cleaning and using old plugs is not recommended because they might still have a tiny amount of oil on them that you cannot see.

However, since the spark plugs are already bad, it would be best to replace them with new ones, which won’t cost you much.

Step 3: Clean the Head and Valve Cover

Remember to always clean the head and valve cover before fixing new gaskets and seals. Doing so will help to get rid of old particles, thereby helping the new parts you are installing to have a tighter seal.

During the cleaning, don’t fail to use the appropriate greaser and only use plastic equipment to prevent the cylinder head or valve cover from getting damaged.

Step 4: Install the New Valve Cover Gasket

It is always essential to provide a new gasket that fits perfectly with the shape of the component. However, do not also fail to examine the parts to know if they are original before buying them for your car.

Often, the high-quality silicone material is recommended as ideal for the durability of your vehicle and valve cover gasket.

Additionally, they do not require constant replacement, as it reduces the work and the expenditure.

Therefore, immediately you get it, first apply a liquid known as sealer around its edges to prevent the new gasket from slipping over.

Furthermore, the gasket placed over the liquid sealer should tightly guard its place, preventing oil from entering the spark plug.

Step 5: Install the Spark Plug Gasket

Finally, position the spark plug gasket correctly on top of the rim of the spark plug. The spark plug gaskets are round-shaped and are installed in the same way using the liquid sealant that acts as the valve cover gasket.

After that, you can bolt the nuts in the 2-3-1-4 order earlier detached to prevent any possible damage to the valve cover.

Tip: if you want to fasten the nuts properly, you must follow the above order. Then, restore everything to its position and endeavor to rinse the oil that would’ve spilled around off the parts using an oil cleanser.

In a nutshell, the spark plugs play a more prominent role than their engine function size. So, it is your responsibility as a car owner always to examine the state of the spark plugs to ensure there is no oil on the spark plug threads.

Check out this video for more tips on how to fix oil on spark plug threads

Can You Drive With Oil on Your Spark Plug Threads?

Of course, you can drive with oil on your spark plug threads, but you’ll have to figure out how it happened. this is because oil on your spark plugs isn’t a normal condition, and it can be a sign of much more severe problem.

The oil on the spark plugs isn’t necessarily – it primarily has to do with how the oil got there that can affect your engine.

Also Read: Car Leaking Oil When Parked? (Causes and Fixes)

Frequently Asked Questions – Oil on Spark Plug Threads

Should There Be Oil on Spark Plug Threads?

No, there shouldn’t be oil on spark plug threads. You can always address the issues that come with oil on spark plug threads by looking out for clustered oil or dirt on the sides of the valve cover after every oil change. Once you discover any oil leak, it would be best to change the gaskets and seals immediately to save yourself from the cost that comes with expensive engine damage.

Can Oil in Spark Plugs Cause No Start?

Yes, oil on the spark plugs can prevent the car from starting. Once oil touches the spark plug, it is usually a sign that the oil has probably shorted out all the plug wires and coils, causing the engine not to start.

What Causes the Oil in the Spark Plug Well?

If a spark plug well is covered in oil, it could be that the O-ring that seals the well to prevent oil and debris has been damaged or worn out and has begun to leak. Even though the leak can sometimes be addressed by tightly fastening the valve cover bolts, the valve cover gasket and well seals will often require replacement.


As discussed earlier, it’s never all doom and gloom to have oil on your spark plug threads.

All that is required of you is to constantly check for clustered oil or dirt on the sides of the valve cover after every oil change.

Once you discover any oil leaks, it would be best to replace the gaskets as soon as possible to avoid potential costly damaging effects on the engine.

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