What Causes Spark Plugs To Get With Oil Or Gas?


Spark plugs are critical components in an engine’s combustion process. They are designed to deliver sparks that ignite the fuel and air mixture inside. However, the portion inside the chamber can sometimes get covered with oil, while the outer part can get wet with gas.

When spark plugs get wet with oil or gas, it’s because those fluids aren’t being contained where they belong. A leaking o-ring seal can be the root cause, though a blown head gasket can also cause the engine oil to leak into the combustion chamber. Besides that, a damaged piston or piston compression seal, as well as compromised valve guides, can also be causes.

You must keep your spark plugs in excellent working condition. So, read through this guide to understand why they’re covered with engine oil or gas and how you can fix the problem quickly.

Why Are My Spark Plugs Covered With Oil Or Gas?

Your spark plugs should never be covered in oil or gas. So when you find them that way, that’s a clear sign you’ve got a problem that requires troubleshooting.

Here are the reasons your spark plugs are covered with oil and fuel and what you can do to fix them.

1. Leaky Seals

Whenever there’s fluid somewhere in your car where it doesn’t belong, the first and most likely reason is that you have a leaky seal. Automobiles rely on many seals to ensure that different kinds of fluids stay contained only in areas where they are needed.

The same is also true for your spark plugs. While part of each spark plug is inside the combustion chamber, the rest must remain dry and free from any signs of oil or gas.

When it gets wet with one or both of those fluids, it’s likely the o-ring seal is to blame. The seal could be damaged or worn out, preventing it from stopping any fluids from covering the affected spark plug.

How to fix it: Thankfully, this problem is straightforward to resolve. First, you’ll have to remove the leaky seals and replace them with new ones. Simultaneously, you must clean the wet spark plug and ensure it’s completely dry before using it.

Read: Can Bad Motor Mounts Or Spark Plugs Cause A Car To Shake When Idle?

2. Blown Head Gasket

The head gasket has a similar function to the engine’s various seals. It ensures that the engine’s chambers are entirely sealed so fluids don’t leak in or out and mix.

A blown head gasket is terrible news for the whole engine because it allows external fluids to mix inside the combustion chamber. 

However, it can also be why oil and gas reach the dry portions of your spark plugs.

You can also think of the wet spark plugs as an early warning sign that your head gasket is compromised. So if you ignore it or delay repairs, you could have worse engine problems.

How to fix it: There is no solution for a blown head gasket other than to replace it with a new one as soon as possible. As you read earlier, a blown head gasket puts the whole engine at risk, not just your spark plugs.

Of course, you’ll have to remove and inspect your wet spark plugs to see if they’re still usable. Otherwise, you must replace them when you get a new head gasket.

Read: Can Bad Spark Plugs Cause Engine Shaking And Loss Of Power?

3. Damaged Piston Or Piston Compression Ring

A portion of your spark plug reaches into the combustion chamber. That’s where it delivers the sparks necessary to combust the fuel and air mixture inside.

Another component that moves up and down that chamber rapidly is the piston. The piston compresses the fuel and air mixture, moving closer to the spark plugs as it does so.

The piston is designed with high precision to ensure it can move smoothly inside the chamber without damaging other components. 

More importantly, each piston has a compression ring that ensures the engine oil doesn’t enter the chamber and coats the spark plug.

Unfortunately, a damaged piston or piston compression ring will compromise the entire engine chamber. When that happens, the engine oil will flood the chamber and coat the spark plug, preventing it from working correctly.

How to fix it: You can fix this problem, but it’ll take time and money. That’s because your engine is damaged from the inside (at the piston) and will need to be taken apart.

The piston will have to be replaced along with its compression ring. That’s the only way to ensure that the engine can function optimally in the future.

Although this is the least of your problems, the affected spark plug will also likely need to be replaced with a new one as well.

Read: Why Is There Oil On My Spark Plug Threads?

4. Compromised Valve Guides Or Seals

Another bunch of critical components in your engine and its combustion system are the valves. Those are the ones that open and close to let air and fuel enter each chamber and later allow exhaust gasses to escape.

Those valves must move with extremely high precision at all times. That’s why they have valve guides to ensure they move in perfect alignment and seals to ensure they remain dry at all times.

Unfortunately, a valve guide or its seal will allow oil and gas to leak and coat your spark plugs if they are compromised. Damage or excessive wear will cause gaps to appear where the oil or gas can escape and spread to parts where they do not belong.

Suppose that’s the reason your spark plugs are coated with oil or gas. In that case, your engine is at high risk of damaging itself from the inside. You must get your car to your preferred mechanic as soon as possible.

How to fix it: The solution to this problem is to replace the affected valve guides and seals. More importantly, you’ll want to inspect all your valve guides and their seals to ensure they’re not affected by the same problem.

It’s reasonable to expect that if one valve guide is damaged, the others are also damaged or will suffer damage soon. 

So, a thorough inspection is necessary to ensure that the same problem doesn’t happen again later.

Read: Why Is There Oil On My Spark Plug Threads?

Do Spark Plugs Covered With Oil Or Gas Cause Problems?

Wet spark plugs might not seem like a big deal at first glance. However, they can lead to a long list of other problems in your vehicle, including:

  • Warnings and indicators: Firstly, a spark plug covered with oil or gas can cause warning lights and indicators to become active. For example, the check engine light might turn on, or your onboard diagnostics will show active fault codes.
  • Misfiring: Wet spark plugs can also lead to misfiring and other issues that prevent the engine from running smoothly.
  • Emissions: Spark plug issues prevent the air and fuel mixture from burning correctly, leading to excessive emissions.
  • Fuel efficiency: Overall, your vehicle will lose its fuel efficiency until the spark plugs work correctly.

Read: What Is A Link Stabilizer On A Car, And What Does It Do? (With Pictures)

Final Thoughts

Spark plugs are relatively tiny components compared to many others in your vehicle. Still, they must remain dry to function correctly.

A spark plug will get covered with oil or fuel if the o-ring seals are worn-out or damaged. A blown head gasket will also cause the same issue, as will damaged pistons and piston compression seals.

In most cases, you’ll have to replace the damaged parts to solve the problems. Still, don’t forget to check the spark plugs and replace them if necessary.

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