Oil On Spark Plugs Causes, Symptoms, and How To Fix It

Oil plays a crucial role as a lubricant in ensuring the smooth operation of your engine. However, oil should not be present on the spark plugs. The presence of oil on spark plug threads is a clear indication of potential larger engine issues that need attention.

Oil On Spark Plugs

While oil is essential for optimum engine performance, its presence on spark plugs can adversely affect your engine’s performance. There are many areas in the vehicle where engine oil shouldn’t be present.

Regardless of the underlying cause, it is imperative to conduct a thorough inspection when you notice oil on spark plugs, to identify the source of the problem. By identifying and replacing faulty components, you can restore your engine to its peak performance. This article explains the causes of oil on spark plugs and how to fix this issue.   

Reasons for Oil on Spark Plugs

There are different reasons why oil leaks onto the spark plugs. Oil usually gets on the spark plugs due to a clogged PCV valve or a damaged valve cover gasket. However, worn intake valve seals, a bad turbocharger, or clogged crankcase ventilation can also be caused by this issue.

The following are the most common causes of oil on spark plugs:

1) Leaking Valve Cover Gasket

Valve Cover Gasket, causes of oil on spark plug

The valve cover gasket is located at the top of the cylinder head. It is subjected to excessive temperatures. Its primary function is to contain the oil within one side of the cylinder head, preventing it from reaching other engine components.

However, when the valve cover gasket starts to leak, it can lead to oil fouling in the area of the spark plug threads and the corresponding spark plug wire or ignition coil. This occurrence can adversely impact engine performance and potentially cause issues with spark plug ignition.

2) Faulty Turbocharger


The turbocharger provides an extra power boost for an exhilarating ride. However, a bad turbocharger is also one of the common causes of oil on spark plugs.

The turbine shaft contains seals that can succumb to the effects of heat over time. As a result, the engine oil can find its way into the intake and engine cylinder, eventually reaching the spark plug. Unfortunately, you will have to replace the blown turbocharger to fix this issue.

3) Clogged Crankcase Ventilation

The primary purpose of crankcase ventilation is to discharge pressure caused by blow-by gases in the crankcase. It redirects these emissions back to the intake manifold to re-burn into the combustion chamber.

When the crankcase ventilation fails, excessive pressure in the crankcase starts to build up, which may lead to oil leaks.

A clogged crankcase ventilation system exhibits similar symptoms to a faulty PCV valve, as both situations result in increased pressure. These symptoms may include a higher-than-normal idle and reduced engine performance.

4) Clogged PCV Valve

PCV Valve

Modern cars are equipped with a positive crankcase ventilation (PCV) system to minimize emissions and promote environmental cleanliness. This system efficiently expels crankcase vapors while redirecting them to be re-burned within the engine.

However, when the PCV valve goes bad or becomes clogged, it can lead to unintended consequences, such as siphoning oil from the engine. This issue increases the production of the vapors and may lead to spark plug fouling with oil.

Read More: Bad PCV Valve Symptoms and Causes

5) Bad Pistons

bad Piston

A bad piston may also cause engine oil on the spark plugs. If there are problems with the pistons, such as cracks or damage, oil can pass from the crankcase to the combustion chamber through these damaged pistons.

As a result, the spark plugs get fouled with oil, and you’ll be challenged with significant problems. Repairing the engine in such cases can be costly, and it may not be economically viable if the vehicle’s value does not justify the investment.

6) Worn Intake Valve Seals

Intake Valve Seals, causes of oil on spark plugs

Intake valves are vital components located in the cylinder head of an engine. The primary function of the intake valve is to facilitate the entry of air into the engine cylinder while assisting in the efficient exit of exhaust gases.

These valves have stems located in the cylinder head. This valve seal is very important to prevent oil from passing through the oil channels and entering the engine cylinder.

However, over time, if the valve seals wear out, it may lead to oil seepage into the system, resulting in fouled spark plugs. Consequently, your engine may start consuming more oil than usual, and you might observe smoke emanating from the car’s tailpipe, especially during the initial engine startup.

7) Leaky Piston Rings

Worn Piston Ring, reasons of oil on spark plugs

The piston ring of your vehicle plays a crucial role in maintaining proper engine function by stopping compression loss and stopping oil from entering the combustion chamber.

The piston rings may experience wear and damage over time.

When piston rings become damaged or worn, they can no longer effectively seal the combustion chamber, allowing oil to seep through. Consequently, the oil ends up fouling the spark plugs, leading to various issues.

8) Leaky O-Ring Seal


Leaky O-ring is also one of the common causes of oil on spark plugs. These O-rings are responsible for keeping coolant, engine oil, and other fluids on one side of the spark plugs, ensuring they remain dry. When the O-ring seals are damaged, engine oil may contaminate the spark plugs.

Addressing issues related to the O-rings promptly is crucial to maintain engine performance, prevent spark plug fouling, and ensure the engine operates efficiently and smoothly.

9) Blown Head Gasket

Blown Head Gasket

The head gasket serves a critical role by sitting between the engine block and the piston head. It effectively seals the combustion chamber and prevents oil from entering the combustion chamber.

It also plays a crucial role in stopping oil deposits on the spark plugs. Additionally, the head gasket ensures that coolant and oil do not mix as they move to the cylinder head via the oil lubrication system.

When a head gasket is blown, it can lead to engine oil seeping into the combustion chamber, causing leaks into the plug wells and eventually onto the spark plugs.

Read More: Bad Intake Manifold Gasket Symptoms and Causes

Symptoms of Oil on Spark Plugs

The oil on the spark plugs produces different symptoms such as poor engine performance, fuel smell from the exhaust, poor fuel economy, blue smoke from the exhaust, engine misfiring, or backfiring.

The following are the most common symptoms of oil on spark plugs:

1) Reduced Engine Performance

Poor Engine Performance due to oil on spark plugs

A reduction in engine performance is one of the most common symptoms of oil on spark plugs.

A minor malfunction in a single engine part can significantly impact its performance. When the spark plug fails to generate a spark efficiently, the engine’s performance reduces, and a direct impact of poor engine performance is a decrease in fuel economy.

2) Fuel Smell from the Exhaust Pipe

If you smell fuel inside your vehicle, it could be a sign of oil on the spark plug. This happens when oil mixes with fuel in the exhaust and produces a distinct fuel smell inside the cabin.

When you smell fuel, it’s essential to get this checked out by a mechanic to fix the issue and ensure your car runs smoothly and safely.

3) Poor Fuel Economy

When the spark plugs are faulty, the engine doesn’t work as well as it should. To make up for this, the engine increases the supply of fuel to the combustion chamber to ensure the right pressure for combustion.

Unfortunately, this causes the vehicle to use more fuel, making it less efficient, and it also leads to higher oil consumption.

4) Misfiring Engine

Misfiring, symptoms of oil on spark plugs

An engine misfire occurs when the engine temporarily stumbles, hesitates, or loses power, especially during acceleration, and then returns to its usual speed.

Misfires can also appear during idle, leading to uneven or rough idle.

However, there are various causes of engine misfires and the oil on the spark plug is a potential culprit. A misfire can happen when the oxygen, fuel, or spark plug is not functioning in the correct order or at a specific time.

When a spark plug is covered in oil, it has a hard time producing a spark and keeping the cylinder at the right temperature. As a result, the ignition can happen too early, too late, or sometimes not at all, which causes engine misfires. This can lead to poor performance and potential issues with your car’s engine.

5) Blue Smoke from the Exhaust

The engine oil on your spark plugs may hinder the electrodes’ ability to produce a consistent spark. This leads to poor combustion, so the engine tries to balance this issue by adding more air-fuel mixture in the combustion chamber.

However, this can result in unburnt fuel exiting through the exhaust valve, causing blue smoke to come out of the exhaust pipe.

6) Engine Backfiring 

Backfiring, signs of oil in spark plugs

An engine backfire takes place when the fuel doesn’t ignite at the correct time. In the presence of oil on the spark plugs, your engine becomes susceptible to backfiring.

The presence of oil on the spark plug may hinder its ability to create sparks precisely when the exhaust valve opens. This timing misalignment can lead to an engine backfire.

How to Fix Oil On Spark Plugs

The first step to fixing the issue of oil on a car’s spark plugs is to find out the exact cause of the problem.

1) Check the System For Leaks

The initial and crucial step is to locate the source of the oil leakage. Merely replacing the spark plugs without addressing the underlying issue will not resolve the problem.

Therefore, it’s essential to fix the root cause of the problem to prevent further fouling of your spark plugs.

Furthermore, neglecting the oil leak and continuing to drive may lead to more significant problems. Running the engine with leaking oil could potentially cause permanent damage, depending on the nature of the issue.

2) Replace Faulty O-Rings

 If you find that one or more O-Rings are damaged, it’s important to promptly obtain replacements. Follow the below-given steps to replace the O-rings:

  • Obtain suitable replacement O-Rings for your vehicle’s engine.
  • Remove the valve cover to gain access to the old O-Rings and allow them to come off.
  • Carefully pry out the old O-Ring from the underside of the valve cover.
  • Install the new O-Ring by sliding it into its designated position.
3) Remove Excess Oil

An excess amount of oil in the engine may also cause engine oil on the spark plugs.

If the problem is attributed to excessive oil in the vehicle, you will need to remove the additional oil. Locate the drain plug and open it to allow the excess oil to drain out.

4) Replace the Faulty Valve Cover Gasket

If you suspect a faulty valve cover gasket is the cause of the oil on spark plugs, it’s essential to replace it as soon as possible. Follow these steps to fix the new gasket:

  • Get a new valve cover gasket suitable for your vehicle.
  • Take away the valve cover by carefully removing any bolts and securing it in place.
  • Remove the old valve cover gasket from its position.
  • Install the new valve cover gasket meticulously, ensuring it installs properly and is correctly aligned.
  • After installing the new gasket, reattach the valve cover securely using the appropriate bolts.
5) Replace the Damaged Piston

If a faulty piston leads to oil leaks into the spark plug area, it’s essential to replace it as soon as possible. To perform this task, you’ll require a piston ring compressor and a dead blow hammer.

6) Replace the Head Gasket

The head gasket is a complex part that should ideally be repaired by a mechanic. If you plan to replace the gasket yourself, proceed with extreme caution.

For optimal safety and accuracy, it is recommended to purchase the necessary part and entrust an expert to handle the repair job.

7) Replace the valve guides

If the valve guide leads to oil on the spark plugs, you need to replace them. Changing a vehicle’s valve guides can be a challenging task. You can follow the below-given steps to replace the valve guides:

  • Start by disassembling the engine to approach the old valve guides. These guides are located in the cylinder head.
  • After accessing the valve guides, remove them carefully from their position using a valve guide removal tool.
  • Install the new valve guides by inserting them into the appropriate locations.
  • Utilize a valve driver to properly put the new valve guides in their place.
  • With the new valve guides securely installed, proceed to reassemble the engine components.
  • As you reassemble the engine, pay close attention to ensure all parts are correctly aligned and tightened.
8) Contact A Professional

Replacing the engine parts is a complex task, even for mechanics, and identifying the source of oil leaks on spark plugs can be challenging. This diagnosis process may be time-consuming.

If you are uncertain about how to proceed, it is crucial to seek assistance from a professional mechanic. Turning to a skilled expert is the best way to ensure that the repairs are done correctly, preventing any further damage to your vehicle.

FAQ Section

Can a bad PCV valve cause oil on spark plugs?

A potential cause for oil leakage into the combustion chamber is a malfunctioning PCV valve. When this valve gets stuck closed, the crankcase pressure may increase, forcing oil into the combustion chamber. This oil accumulation on the spark plug tips can cause fouling, affecting engine performance. Repairing the root cause is essential before changing the spark plug.

Can oil make spark plugs go bad?

Yes, oil on the spark plug tip is one of the most common causes of its early failure. An oil leakage indicates a problem that requires immediate resolution before installing a new spark plug. The presence of oil in the combustion chamber is undesirable, and addressing the underlying issue is crucial to prevent further complications.

How much does it cost to replace a valve cover gasket?

Valve cover gasket replacement typically costs between $90 to $360 on average. The part required for the repair is relatively cheap, ranging from $10 to $60. However, the labor cost is very high, which usually ranges from $80 to $300.

What does an oily spark plug look like?

If you see black, oily deposits on the spark plug, it means the spark plug is oil-fouled. This issue is likely caused by oil leaks into the combustion chamber, which could be due to damaged valve guides or piston rings.

Can oil in spark plugs cause no start?

When oil gets into the spark plugs, starting the vehicle becomes challenging. Over time, the oil’s presence may also demolish the performance of the ignition coil and the spark plug wires, leading to engine starting issues. However, this is a frequent symptom observed in the case of oil on spark plugs.

Can oil ruin a coil pack?

Yes, but oil can’t directly cause immediate damage to a coil pack since it is located in an oil-filled housing. But the oil leaks may lead to coil pack issues if the excess heat causes the housing to break and damage the coil. Oil leaks pose a serious threat to the ignition coil and can result in significant issues.

Can I drive with Oil on my spark plugs?

Yes, you can drive with oil on spark plugs for a short time, but driving for a long time is not recommended. It may cause engine misfires and potential damage, so it’s essential to address the issue before driving the vehicle.

How to clean oily spark plugs?

To clean the oily spark plugs, it is essential to first address the root cause of the oil leakage on the spark plugs. Once the underlying issue is fixed, you may proceed with the cleaning process. Start by spraying carb cleaner into the affected area and utilize a rag to wipe away the oil. Repeat this procedure as necessary until all traces of oil are removed from both the affected area and the spark plug.

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