Why Is There Oil In My Spark Plug? (11 Reasons Why)

Oil in your spark plugs can be a severe problem. This is because the oil in a car’s engine is constantly being consumed and reused. As a result, it typically gets dirty and always has the potential to create issues.

Therefore, unwanted oil can permanently damage spark plugs and severely affect the engine itself. Here are a few causes of oil in your spark plug socket that you might observe!

Why Is There Oil In My Spark Plug?

If you’re experiencing excessive oil on your spark plugs, it’s likely because you’ve been running your car with too much oil. Over time, the gas can seep into the plug and mix with the lubricant, which blocks the spark gap. As well as that, if your viscosity is thinner than gasoline, it can lead to this issue and engine misfiring!

Listen up as we’ve highlighted the most frequent causes and focal points of oil on spark plugs!

1. Excessive Oil

Spark plugs have a small amount of oil added to them when they’re manufactured.

On the other hand, if the oil level climbs too high, the moving parts of the engine, particularly the crankshaft, may spray oil excessively.

Eventually, the oil will splash into the cylinder and go into the spark plugs, blocking them.

As a result, your spark plugs may have too much oil in them, so you should reduce how frequently you use them until they stop wearing out as quickly!

2. Mixture With Gasoline

When you mix gasoline with air, it produces carbon dioxide and water vapor, condensing into liquid when exposed to cold temperatures.

Meanwhile, since oil is less thick than water, it will “float” on the liquid.

Due to this, if your engine isn’t getting enough air from the intake manifold, these vapors will build up inside each cylinder until they reach an equilibrium point.

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When this happens, the spark plug’s coating will collect some of the oil from the engine and store it there until you change it out for a new one!

3. Thin Viscosity

Another reason oil is present in your spark plug is due to the viscosity of your engine oil. The thinner the oil, more likely it is to allow air through and create a spark gap.

Besides that, it is because engines run continuously at high temperatures, which would cause the oil to become burned off or evaporate.

With less viscosity and thus less thickness, there is no way for that heat to be transferred away from the spark plug itself.

Generally, if the oil is applied too thinly, it may pass the piston and get to the spark plug!

4. Cracked Cylinders

Overheating is the most frequent reason for cylinder head fracture. The head expands as the engine quickly heats up, then contracts as the engine cools.

In certain cylinders, a broken cylinder head may not produce the necessary environment for proper combustion.

When this happens, oil can enter the combustion chamber and burn alongside the gasoline and air combination.

Therefore, if your engine has a problem with cracks in its cylinders, oil is possible to leak during operation!

5. Deteriorated Engine

In a handful of seconds, a vehicle engine can be destroyed. One contributing factor is the excessive hydrogen content of gasoline.

Due to this, the engine might rust because of the gas tank’s acid. Also, as already mentioned, mixing gasoline and water causes an impact.

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This is why, if you have been running your car for long periods without properly maintained coolant levels, you may notice that your spark plugs are covered in oil!

6. O-Ring Seal Drips

O-Ring Seal Drips

O-ring seals frequently break down in dynamic applications due to increased friction from repeated contact between the O-ring surface and the housing.

Consequently, the risk can be increased by using the wrong lubricant and allowing abrasive impurities into the sealing system.

Above all, these O-rings keep one side of the spark plug dry and the other side covered with oil and everything else.

So, a dripping O-ring seal may be the cause of just one spark plug having oil!

7. Busted Head Gasket

A broken head gasket can cause too much pressure to build up in the cylinder head and keep it from sealing correctly with its head bolts.

Apart from this, it causes more oil to leak out than usual, filling up your spark plug holes and causing wear on its insides over time.

Under these circumstances, if your head gasket has failed, coolant will leak into your engine block, which can lead to oil being present on your spark plugs!

8. Frayed Valve Guides

Valve guides are the metal pieces that direct the oil flow to your spark plugs.

Evidently, if they’re not properly aligned with each other, you can experience oil oozing onto your spark plugs.

If those seals fail, oil enters the combustion chamber, where it is only a matter of time before it contacts the spark plug gaskets!

9. Valve Cover Gasket Leakage

A valve cover gasket is a thin, rubber-like material that covers the top of each valve cover, connecting it to the cylinder head.

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When the engine is running, an oil-covered valve cover or an odor of burning oil are signs that the valve cover gasket failed to seal.

By all means, spark plugs can become contaminated with oil if the valve cover gasket leaks!

10. Exhausted Piston Compression Rings

When a piston is used to compress and expand, the rings will be worn out.

Naturally, it indicates that the area around your spark plug’s insulator is less compressed, which reduces the spark plug containing oil.

Because of this, your spark plugs will start to accumulate oil because the piston’s rings can no longer compress as much!

11. Drained Pistons

Pistons may break when using poor fuel frequently due to a broken exhaust gas recirculation system.

Apart from this, if you have a problem with your piston when you start up your engine, there may be some excess oil on your spark plug insulator.

As an effect, when a piston is drained, this leaves them without oil, which then collects on the spark plugs!

To know more, you can also read our posts on why Michigan car insurance is so expensive, why your Abs light is on, and why your battery light is on.


Oil is an inevitable part of your engine’s operation. It lubricates moving parts and keeps them from wearing out or wearing down.

In most cases, oil is present in your spark plug because of excessive fat, mixture with gasoline, and thin viscosity.

Ultimately, your spark plugs are designed to work with a certain amount of oil at some point. So now that you’ve figured out why it’s happening, it’s time to clean your spark plug!

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