What Causes Oil on Spark Plugs and How to Fix it

Oil is necessary to ensure that your car and engine are functioning properly, but sometimes you will find them in places they should not be in.

Perhaps, while you were performing standard maintenance, you saw splotches of oil on the spark plug threads. Or, while diagnosing the cause of your vehicle’s low oil level, you may have discovered oiled spark plugs. Finding oil on your spark plugs can indicate engine trouble that could cause further damage if not mitigated.

In this article, we will be taking a look at what causes oil on spark plugs and going over how to fix these issues so you can take better care of your engine!

What is the function of a spark plug?

Spark plugs are tiny electrical devices that convert thousands of volts of electricity into sparks intended to ignite the mixture of fuel and air in all gasoline-burning internal combustion engines.

In addition to removing heat from the combustion chamber, a spark plug generates an electric current between its ground and centre electrodes. This current or “spark” resembling a small lightning strike ignites the air-fuel mixture in an engine’s combustion chamber, causing the engine to operate.

This ignition causes a controlled mini-explosion, the energy from which is used to power the engine. Pressured gas and air pushed by the piston into the cylinder heads of engines are ignited by their spark, slamming the piston back in a fraction of a second. The exhaust pushes the piston back as additional fuel and air are drawn into the cylinder, and the cycle repeats.

Why is there oil on my spark plugs?

Once you notice oil on your spark plugs, you must figure out where it came from. If the spark plug gasket is not leaking, what else could be happening? We’ve outlined below the most frequent causes of oil on spark plugs so you can narrow it down when you diagnose it yourself:

1. Faulty O-ring seals

While spark plugs may not have gaskets, they do utilise O-rings. O-rings, which may be external or incorporated with the valve cover gasket, are placed around the spark plug holes to prevent oil and other contaminants on one side of the spark plug while the other side remains dry.

When these deteriorate due to heat, they will begin to seep oil into the spark plug holes. If there is oil on only one spark plug, the O-ring seal may be leaking.

This is one of the best outcomes if your spark plugs are oiled. Nevertheless, you must address the issue as quickly as feasible. This is detrimental to the ignition coils and spark plugs since it can cause misfires and lead to failure.

If your spark plugs are entirely encrusted with oil, you should replace the valve cover gasket and the O-rings surrounding the spark plugs.

  1. Defective Piston rings

Broken piston rings are an additional cause of oil on spark plug threads. Above and below the piston are piston rings that prevent oil from entering the combustion chambers of an automobile. These are metallic split rings attached to the piston’s outside diameter.

These rings also contribute significantly to removing surplus oil from the cylinder walls. Currently, the engines of automobiles have three pistons per cylinder. The top two compression rings help seal the combustion chamber, while the bottom ring, known as the oil control ring, controls the oil supply to the cylinder wall to lubricate the piston skirt and oil control rings.

It also aids in removing excess oil from the cylinder walls to prevent residue from entering the combustion chamber. However, once these piston rings cease to operate correctly, the oil will leak into the combustion chamber, thereby contaminating the spark plugs. In such a scenario, you would smell motor oil throughout the cabin. Additionally, you would observe daily blue exhaust from the vehicle.

  1. Damaged Piston

Besides having a defective piston ring allowing engine oil to leak into the cylinder and saturating the spark plug, a blown piston can also result in oil saturation of the spark plug well. Due to extreme heat, the piston may rapidly begin to fracture.

When a piston is cracked or fractured, the spark plugs may become saturated with oil. In addition, because the engine generates so much heat during operation, the piston can sometimes overheat, resulting in cracks.

Due to the fissures, oils flow into the combustion chamber and spark plugs. In other words, when piston rings are damaged, oil has probably poured into the combustion chamber. If the piston is cracked or damaged, you may experience a loss of power, a misfiring engine when driving, and a rattling or knocking noise.

Driving your vehicle with a damaged and overheated piston could cause significant engine damage, especially if you neglect to repair the issue properly. Additionally, any delay in replacing it could result in increased repair costs.

  1. Blown-out head gasket

The head gasket is the most crucial gasket on a car. It is located between the engine block and the bottom of the cylinder head, preventing oil and coolant from leaking. They are composed of a superior type of rubber(elastomer) and steel, allowing them to seal between the two components.

Since coolant and oil move from the engine block to the cylinder head, the head gasket serves to seal the internal combustion chamber and prevents coolant and oil from mixing. However, the component might break with time, resulting in oil leaks into the engine compartment’s spark plugs and other sections. In the event that the head gasket fails, the oil will flow into the combustion chamber and spark plugs.

Symptoms of a blown gasket include:

  • Milky white oil.
  • White smoke from the exhaust pipe.
  • Coolant is leaking outside the engine from underneath the exhaust manifold.
  • An overheated engine due to a lack of coolant due to leaks or bubbles in the radiator or coolant overflow tank.

A ruptured gasket must be replaced immediately. It is not recommended to drive a vehicle with a blown head gasket, as doing so might cause significant engine damage.

  1. Worn-out valve guide seals

The valve guides assist with the admission of air into the automobile’s engine, securing the valves throughout this process. The valve guide seals are effective, but with continued usage, they may begin to show signs of wear.

Eventually, you may need to replace them, as this would prevent oil from reaching the spark plug well. If you fail to do so, you may have severe issues, as oil should not reach the spark plugs.

  1. Malfunctioning valve cover gasket

The valve cover gasket is one of the most vital of a vehicle’s several gaskets. This component creates a seal between the cylinder head and the valve cover by sitting between them. The valve cover gasket ensures that oil injected into the cylinder head is directed to the camshaft, valve springs, valve guides, etc.

However, the valve cover gasket is likewise comprised of silicone or rubber; it deteriorates due to heat or prolonged use. This flaw will render the component inoperable and allow oil to flow into the spark plug region.

How do I remove oil from spark plugs?

It is essential to learn how to change the oil in spark plugs. If you detect oil leaking from spark plug motorcycle engines or oil on the threads of your spark plugs, you can correct the problem by following the procedures below:

  1. Take off the spark plugs

Using the appropriate instrument, remove all spark plugs and examine the oil for oil residue. It would be helpful if you also inspected them for wear and replaced the damaged plugs. If you have difficulty doing so, you might get advice from an expert.

  1. Replace faulty O-rings

Once you have determined that one or more O-rings are defective, please replace them as quickly as possible.

To remove the old O-rings, the valve cover must be removed. Then, pry them out via the underside of the valve cover. Install the replacement O-rings by sliding them into position. Coating the O-rings with a little layer of oil before insertion will lubricate and ensure good seating.

Ensure that the O-rings are installed correctly, with the tapers pointing squarely towards the engine.

  1. Replace damaged pistons

Please replace the cracked or damaged piston that could be causing oil leaks into the spark plug area. This task will require both a dead blow hammer and a piston ring compressor. However, if you are unsure of your ability to fix the component correctly, please consult a skilled auto mechanic.

  1. Remove valve covers

To view the spark plug, you must attempt to remove the valve cover. This can be accomplished by carefully removing the bolts. It may appear to be quite tight; therefore, a suitable tool is required. Be careful not to harm the cylinder head while attempting to remove the bolts.

  1. Change the head gasket

The head gasket is a complex component that trained auto mechanics can only repair. If you wish to install the part yourself, exercise extreme caution. However, We highly recommend that you purchase the component and have a professional perform the work to be safe.

Bottom Line

This article aims to provide essential information regarding the causes of oil on spark plug threads and the accompanying remedies. So, there is no need to panic if you are now facing this difficulty. Please determine the exact reason for the oil leaks near the spark plugs and follow the treatment provided above.

Although finding oil on spark plugs can be an issue, oil additive can also help alleviate other issues such as engine knocking.

If you are doubtful about your ability to perform the procedure precisely, you should consult a professional automotive mechanic to assist you and make your life easier!


As a user of The Automotive Men (theautomotivemen.com), please note that we participate in the Amazon Associates Program. This means that “As an Amazon Associate, I earn from qualifying purchases.” We are not directly sponsored or endorsed by Amazon, but our website may contain affiliate links that provide us with a commission when you make a purchase through them. Thank you