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Oil On Spark Plug Threads : Here’s Why & The Fix [ 2022 Updated ]

Oil On Spark Plug Threads : Here’s Why & The Fix [ 2022 Updated ]

Automobile owners habitually lubricate their vehicles to maintain the engines’ proper functional conditions. While oil happens to be indispensable to keep your car running, finding oil on the threads of your spark plugs wouldn’t be a good sign.

Perhaps, you had been carrying out the regular maintenance, and you came across oil on these threads. Remember, lubricants and engine oil would only be useful when they remain in the allocated zone in the car. Fuel, oil, and water should never mix in the wrong place. This might lead to misfire, and inflict damage to the engine.

When oil gets into the combustion chamber, you would find it on the threads. This article explains why you might find oil in the spark plug threads and how you can resolve the issue.

What is a spark plug?

The function of spark plugs is to convert electricity to sparks that are capable of igniting the mixture of air and fuel in the combustion chambers of cars. These plugs are electrical devices, small in size, that cause a controlled explosion for the car’s engine to harness the energy.

The spark ignites the pressured air and gas that eventually helps cars to start their engines. Therefore, these components are necessary for the engine to perform its task effectively.

Is it bad if my spark plugs have oil?

Yes, having oil on your car’s spark plugs wouldn’t be a good indication. So, when you troubleshoot the engine or regularly maintain your car, keep an eye on the spark plug threads. If you find oil leaking in these mechanical parts, make sure to address the issue immediately.

Now, car owners should understand the intensity of the issue. Leaking oil on the spark plug threads might not cause seizure of the engine or any extensive damage.

However, if you continue to operate with the condition, you might end up with broken valves and warped pistons.

In case the spark plugs get the oil ignited, you also have a chance of engine fire. If you fail to address the issue, your car might fail smog tests. Prolonged issues with this leaking oil would harm the head gasket.

Why is there oil on spark plug threads?

Leakages in the valve cover gasket are the most common factor leading to the presence of oil on spark plug threads. When you detect oil on the electrode of your spark plug, it might also point to clogged ventilation in the crankcase, malfunctioning piston rings, poor sealing of the intake valves, or problems in the turbocharger.

We have explained all the possible causes leading to the presence of oil on spark plug threads.

1. Leaking valve cover gasket

Your car has valve cover gaskets to ensure that the oil remains close to the required parts. So, it prevents it from flowing to other chambers that don’t need any oil. Since the spark plugs do not need oil, the valve cover gasket keeps it away from this component.

However, if you leak the valve cover gasket, it seems into other parts, such as the spark plugs. Although replacing these gaskets involves significant physical labor, these parts come relatively cheap.

So, the oil in this case doesn’t come from the engine’s interior. Rather, it flows in from the external part of the valve cover, and thereby fills the wells up.

2. Clogged ventilation around the crankshaft

Sometimes, you might detect oil present on the tip of the spark plugs. This implies that the oil originates from the combustion chamber. If this occurs, you need to address the issue immediately, as you wouldn’t expect oil to be present in the combustion chamber.

A faulty or clogged ventilation of the crankcase might lead to this issue. As a result, the area inside the crankcase develops excessive pressure and the oil flows into the combustion chamber. It may enter the combustion chamber through piston rings, turbocharger, valve settings, or the crankcase ventilation.

It is imperative to inspect the crankcase ventilation to ensure that there are no clogs in the system. In case your model has breathing valves, they should be perfectly operational.

3. Damage in the piston compression rings

You will notice compression rings present around all the pistons in the car’s engine. In case these rings sustain damage, the oil would undoubtedly get into the combustion chamber.

To prevent potential issues, make sure that the piston compression rings are in good condition. Now, if you find that these rings have sustained damage, make sure to get them fixed at the earliest.

4. Intake valve seals wearing out

In the combustion chamber of your vehicle’s engine, the intake valves have a significant role to play. It regulates the inflow of fuel and air, while controlling the outflow of the exhaust gasses.

Under no circumstance should the engine’s coolant, oil, and fuel mix. In case the seals of the intake valves wear out, the oil tends to leak into the combustion chamber.

If this happens, you would detect blue smoke from your car. Try to get the valves fixed at the earliest, so that there’s no potential issue with the engine.

5. Problems in the pistons

A defective piston might also lead to oil leakage into the spark plugs. Pistons suffer regular wear and tear since they operate at high speeds. So, if you have a melted piston, or damage or cracks in these components, it provides a way for the oil to get into the spark plugs.

So, if you find oil in the threads of your spark plugs, make sure to carry out a leak-down-test. A compression test would also help you determine whether the issue lies in the pistons of the engine. With the right equipment, you can quickly diagnose the issue.

6. Leaking or worn valve guides

The function of valve guides is to make sure that the exhaust and intake valves remain in the right positions. These guides also go a long way in restricting the oil out of the combustion chamber.

In case these seals sustain damages, the oil would enter the combustion chamber. In these cases, the best solution is to go for a replacement. Remember, these valve guides won’t cost you much. However, replacing them involves a lot of manual labor and time. This can lead to high bills when you go to the repair shop.

7. Leaking O-ring seals

In some cars and trucks, there might be no spark plugs in the gasket. Instead, these vehicles have O-rings. The function of these rings is to keep the oil in the right place, so that the other side of the spark remains dry.

In case you find oil on a single spark plug, it points to a leaking seal of the O-ring.

So, if you find oil on the threads of your spark plug, there’s always a possibility that the O-ring seals are leaking. In this case, you need to fix the issue quickly as the problem might aggravate and lead to engine failure. Besides, there’s a chance of misfires in the engine, which might cause even more damage.

How do you fix oil on spark plugs?

In the first place, car owners need to diagnose the issue and find the exact issue leading to the problem. So, when you refer to the reasons leading to issues with oil leakage in the threads of your spark plugs, you can come up with the suitable solution. Here are some of the recommended actions depending on the exact reason for the issue.

1. Remove excess oil

If you find excess oil in your car’s engine, you need to drain it out. Firstly, you need to locate the drain plug and open it on the engine’s oil pan. This ensures that the additional oil would flow out.

However, locating the oil would require you to raise the vehicle. You might also consider using an oil extractor pump for the purpose. This will help you do away with the additional oil through the dipstick or oil cap.

2. Valve cover gasket replacement

You need to replace your valve cover gasket in case it has damage or turns out to be defective. To replace the new gasket, you need to put aside the cover of the valve and do away with the valve cover gasket. You would find a rubber strip along the edges of the valve cover.

Install the new valve cover gasket carefully once you remove the existing one. Once you install the gasket, put back the valve cover in place.

3. Faulty O-ring replacement

If you have malfunctioning O-rings, you need to replace them in two ways. Firstly, you need to take the valve cover off, so that the O-rings easily come out.

Then you need to move them out through the underside of the cover. Once you have done this, slide the new rings in place. It would be wise to put a thin oil coating on the O-rings to form a layer.

Then simply slide them in. This ensures that the system would remain properly lubricated and function properly. The tapers should point to the side of the engine.

4. Head gasket replacement

The head gasket is complex, and you need skilled mechanics to work on it. Simply purchase the component and leave the rest to the experts.

5. Cracked piston replacement

As you know, oil leaks in the spark plug threads may happen if you have a broken piston. So, if this is the issue, you need to get the piston replaced. It would be wise to get an expert to replace the cracked piston if you are unsure how to proceed.

6. Get a new valve guide

It would be a complicated task for you to replace the valve guides of your truck or car. Firstly, you need to get the engine dismantled. Only then would you get access to the parts in your car’s cylinder head.

When you find these valve guides, you would need a specialized tool to do away with the old parts. Next, you can install the new ones. Also, you would need a valve driver that would help push the component back to place. Lastly, you can reassemble the vehicle’s engine.

Can oil leak through spark plug threads?

Yes, the spark plugs threads may leak oil, and you should fix the valve cover gaskets. Never delay replacing or fixing this issue, as it might lead to a greater amount of damage to the car’ engine.

Can You Drive With Oil On Your Spark Plugs?

Technically, it is possible to continue driving if you have oil on the spark plugs. However, it’s imperative to dig out the reason for the presence of oil in a place where it should not be.

Under normal conditions, your spark plugs shouldn’t have oil on them. The underlying issue might be serious, and it’s worth diagnosing the problem at the earliest. Unless you find out the issue, you risk damaging your engine.

Should you Clean and Reuse Spark Plugs?

Yes, you can use the existing spark plugs once again when you get them cleaned. Make sure to get the necessary repairs done. Then you might spray the threads and electrodes using a carb cleaner and let the components dry. Later, you can reinstall the spark plugs and use them just like before.


We have explained every possible reason that might lead to the presence of oil on the spark plug threads. Besides, you are not aware of the respective solutions for each issue.

When you feel that an expert hand would be beneficial, don’t hesitate to reach out to a reputed automobile technician or a repair shop. Your car’s engine is a vital component, so it would be wise not to trouble it yourself.