Oil Fouled Spark Plug: Is It Bad and What to Do? (Explained)

Oil fouling happens when the engine oil reaches the combustion chamber and covers the spark plug. When such a thing happens, it keeps the spark plug from getting through space. If you’re not familiar with spark plugs, you may wonder if it’s normal to happen or if it’s something problematic that needs immediate action. Thus, you may ask:

If you have an oil-fouled spark plug, is it bad? And what should you do with it if it ever happens to you? An oil-fouled spark plug usually happens as a sign of engine wear. In general, it’s not a good thing since oil shouldn’t cover the spark plug. Thus, you’ll need to solve it so your engine won’t have any problem. If left unchecked, it can cause more issues with your engine.

If you’re not familiar with this issue, oil fouling can seem worrisome and daunting. However, it only needs a proper solution, and you’ll be good to go. On the other hand, if you ignore it, it can lead you to more issues to solve in the future.

In this article, you’ll see an in-depth take on an oil-fouled spark plug and what happens with such an issue. This way, you can know how you can deal with it if it ever happens to you. Also, it can help you prepare and prevent it from happening.

Without further ado, let’s get into it!

Oil Fouled Spark Plug

What Does an Oily Spark Plug Mean?

The first thing to understand is the meaning of an oily or an oil-fouled spark plug. So, what does it mean? If you have an oily spark plug, you have too much oil mixed with the fuel. 

Another thing to note is that an oily spark plug means your piston rings are likely failing. It usually happens when the valve seals and stems get worn out. When these valves are down, the oil can slip through, reaching the cylinder and coating the spark plug.

In short, the oil in a spark plug is usually an effect of worn valve tip gaskets, leaking O-rings, or worn piston rings.

From such a perspective, we can say that an oily spark plug means you have issues with your engine and that you need to fix it soon. Therefore, try to replace the spark plugs as soon as you find some oil on them. Moreover, try to have the valves, and the cylinder checked for oil leakage.

Is It Normal to Have Oil on Spark Plugs?

It’s not normal to have oil on spark plugs, and so if your spark plug has some oil in it, it means your engine has some issues you need to address.

As I mentioned earlier, these problems usually come from worn-out spark plug tube seals or covers.

In general, the oil isn’t actually on the spark plug per se. Instead, the oil pools up in the bottom of the cylinder where the spark plug sits. For this reason, you’ll get your spark plug covered in oil when you pull it out.

For this reason, we may conclude that an oily spark plug indicates a problem with your engine that must be addressed as soon as possible. Therefore, if you notice any oil on the spark plugs, try to change them as soon as possible. Additionally, have the valves and cylinder inspected for oil leaks.

What Happens When Oil Leaks Into the Spark Plugs?

When oil leaks into the spark plugs, it’s not good since it can affect the engine by causing problems.

For instance, the presence of oil in the spark plug wells will significantly impact the engine’s performance, resulting in misfires, higher oil consumption, and blue exhaust.

It can also cause an engine fire in extreme circumstances. So if these symptoms appear on the car, you should check the spark plug and the rest of the engine.

This way, you can make sure that your engine is running well and that no oil leakage will cause more damage in the future.

Can I Drive With Oil in My Spark Plugs?

Due to the extremity of the oil-fouling effects, you shouldn’t drive with oil in your spark plugs. While it’s true that your car may run even with oil-fouled spark plugs, it doesn’t mean it’s safe and worry-free to do so.

Oil in a spark plug may cause severe damage to various parts of the engine, such as bending or breaking valves and pistons or damaging the head gasket, all of which can lead to more severe issues.

If not addressed, it will degrade engine performance and cause the engine to heat up, and even cause a fire.

For this reason, take it as a rule of thumb to stop your engine or prevent yourself from driving your car if you have oil in your spark plug.

oil fouled spark plugs

Oil Fouled Spark Plugs Symptoms

If you want to know if you have oil-fouled spark plugs, you can always check your car for the signs or effects caused by such. 

In general, oil fouling happens when oil reaches the combustion chamber and reaches your spark plugs. In short, it means the oil deposits can cover the spark plug, keeping the spark from reaching the gap.

Here are some of the things you can look for to know if you have an oil-fouled spark plug or not:

Oil deposits in spark plugs

A spark plug that has been fouled with oil has a glossy, black look. Deposits can form on the porcelain, shell, or tip whether there is enough oil in the combustion chamber.

Engine oil scent in spark plugs

If you’re not sure if the fouling is caused by carbon or oil, sniff the plug; it should smell like motor oil. The oil might be coming from the piston rings, valve stem seals, or the PCV system (positive crankcase ventilation).

A leak-down test can be used to detect leaking piston rings. In addition, a comparative pressure check might assist in determining structural faults with one cylinder when it has oil fouling.

PCV system issues

In today’s engines, faulty PCV systems are becoming a significant source of oil fouling. More than merely a spring-loaded check valve, these systems have evolved. 

Systems today can isolate oil from crankcase fumes and control whenever the engine consumes the fumes electrically.

Freezing valve

A heater comes in specific PCV systems to prevent the valve from freezing in certain situations, such as when moisture is present. 

If the valve freezes, greater crankshaft tension might result. In addition, the spark plug’s tip may be pushed past the valve covers as a result of such.

Failing turbo-charger

Another reason for spark plug oil clogging is a faulty turbocharger. The seals on the turbine shaft are strong, but heat and poor oil quality can cause them to fail. The lubricating oil for the shaft can enter the pressured inlet and, finally, the cylinder head.

Oil Fouled Spark Plug Fix

If ever your engine suffers from an oil-fouled spark plug, you can always get it fixed by an expert or fix it yourself. If you plan on doing the latter, you can do the following:

Use a carb cleaner.

If you have a fouled spark plug, use carb cleaner to remove the deposits. Use a brass wire brush to remove stubborn residues. Don’t worry since the electrode will not be harmed by the brass.

You may also want to check if the issues are caused by a fouled spark plug. In general, you can check through the following steps:

Drive your vehicle at high speeds.

Take your car out on the highway, start fast, and run it for 15 to 20 minutes at freeway speeds. If the fouling isn’t caused by anything exceptional, this method should clear the plugs.

Check if it’s worn out and fix it.

It’s possible that the spark plugs are filthy or worn if they continue to misfire due to fouling. Take the spark plugs and check them, then clean or replace them as needed.

Spark plug cleaning devices, which sandblast the spark plug’s tip to clear sediments, are available at car parts shops.

Make sure no deposit or particle remains.

If you utilize one of these devices, ensure no sand is caught between the electrodes and the shell before reinstalling the spark plugs in your engine.

Also, make sure the spark plug electrode spacing is restored to the manufacturer’s standards (which needs a spark plug gapping equipment or feeler measure).


In a nutshell, an oil-fouled spark plug is not a good thing, and it means you need to fix something in your engine. The reason is that when oil enters the combustion chamber and reaches your spark plugs, it causes oil fouling. Simply said, oil deposits can block the spark plug, preventing the spark from entering the gap.

If left unchecked, this issue can lead to more problems in the future. Thus, take it as a rule of thumb to have it checked as soon as possible. By maintaining the spark plug, you can prevent a load of problems from occurring in your vehicle.



Image credits – Canva

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My name is Hank, and I've been in the automotive industry for 27 years. I've been working in my own auto repair shop for the last 13 years, and now I want to help you here, on my blog. Let me know if you have any questions. Read more