6 Common Oil on Spark Plugs Symptoms

Naomi O'Colman

Updated on:

Oil on Spark Plugs Symptoms

Oil on Spark Plugs Symptoms

Do you know oil on spark plugs symptoms? Oil serves a variety of functions in a vehicle’s engine, including cooling and lubricating metal parts. However, as crucial as oil is, there are several places where it should not be used, such as spark plugs.

When you see oil on your spark plugs, you know there’s a problem that needs to be handled before it leads to additional, more significant, or even fatal engine issues.

6 Common Oil on Spark Plugs Symptoms

The following are some of the most prevalent signs of oil on spark plugs.

1. Bad fuel economy

A noticeable loss in fuel economy is a common symptom of oil on spark plugs. The failure of the spark plug to provide a decent quality spark is the primary reason for increased fuel consumption. When new, spark plug tips can withstand temperatures of up to 500°C. If oil gets down onto a spark plug tip at this temperature, it will soon burn and leave a burnt oxidized layer on the spark plug tip. A burned spark plug will not perform efficiently or reliably to generate a spark.

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The ECU will try to compensate for the spark plug’s underperformance by raising the amount of fuel in the combustion chamber to maintain the same pressure. This is why oil on spark plugs and is no longer functioning properly, the fuel economy can suffer.

According to some research, faulty spark plugs might result in a 30% rise in energy usage. That’s a massive increase, comparable only to faulty fuel injectors.

2. Engine performance decrease

A spark plug that comes into touch with motor oil, as previously stated, will not be capable to produce a spark for very long. Because the engine oil contaminates the spark plug tip, it is unable to generate a spark that is capable of igniting the fuel and air mixture in the combustion chamber.

If the gas mixture in the combustion chamber does not burn efficiently or entirely, the pressure required to push the piston with adequate force when the engine is under load will not be generated. If you press your foot on the gas pedal and expect the car to accelerate, you’ll likely notice a substantial lag as the ECU and the other spark plugs try to give the power it needs to the wheels.

3. Smoke from the tailpipe is blue

If the spark plug tips are clogged with oil, it will reduce the efficiency with which the engine burns fuel.

The spark plugs’ job is to deliver a spark at exactly the appropriate time, in sync with the timing of the engine valves. This should happen between the valve’s opening and closing, and at exactly the appropriate time and in the correct order. When the timing or quality of the spark is incorrect, it has a negative impact on the combustion process, making it significantly less efficient because the fuel does not burn entirely.

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The engine ECU will try to repair a drop in fuel combustion efficiency by changing the fuel to air ratio in the cylinders if there is oil on the spark plugs because they are no longer functioning as they should. This frequently results in a higher volume of gas utilized by the engine, which causes it to run rich. If there is too much fuel in the combustion chambers, unburned fuel can escape through the exhaust valve and into the exhaust. The exhaust gases may seem blue or white as a result of this.

4. Engine misfires could occur

Engine misfires are another common indicator of oil on one or more spark plugs. The imperfect combustion of the gas and air mixture within one or more of an engine’s cylinders causes an engine to misfire. When you apply force on the accelerator, this seems like a pause or tremor. Oil in the spark plug well or on the electrode tip of a spark plug will prevent it from producing a high enough spark to ignite the fuel/air mixture completely. A power loss from the cylinder piston will ensue, which can show as an engine misfire.

5. Exhaust pipe smells like gas

The smell of gas from the exhaust is another impact of gas not being burned completely in the combustion chamber. Oil on spark plugs frequently causes a gas smell from exhaust fumes, particularly when the engine is cold or just started.

The reason for this is that the engine will frequently use a somewhat richer gas/air mix at the beginning. This is due to the fact that cold fuel is more difficult to evaporate, requiring more fuel to produce a combustible air and fuel mixture. If there is oil on the spark plugs, it will exacerbate the cold fuel problem by allowing more gasoline to be poured directly into the exhaust, resulting in a strong gas odor.

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6. The engine catches fire

If the gasoline in the combustion chamber does not burn fully, it escapes through the exhaust valves and into the exhaust pipe.

When the gas/air mixture in your car combusts after it exits the combustion chamber of an engine cylinder, it’s called an engine backfire. Fuel particles that do not burn properly in the combustion chamber will reach the exhaust pipe with a high energy charge. Mini-explosions or backfires will be used to release this energy.

Engine backfires are not ideal and, if not addressed, can cause harm to your car’s exhaust or intake system. It also has a negative impact on fuel economy and engine performance.

What Causes Spark Plug Oil?

Oil on Spark Plugs Symptoms 2

One of the few elements in close touch with the combustion process is the spark plug. In contrast, engine oil should never come into touch with spark plugs. So, how does oil get to the spark plugs of an engine?

1. The valve cover gasket is leaking

The valve cover gasket is another component that is frequently fitted on the cylinder head, in addition to the spark plugs.

The valve cover gaskets are designed to keep engine oil confined to the cylinder head and away from other engine parts that do not require oil to function properly, such as spark plugs.

The valve cover gasket wears out and is damaged over time due to the high operating temperatures in the engine. This means that it won’t be capable of keeping oil out of other parts of the engine, and some of it may leak into your spark plugs.

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2. O-Ring seal leak

One of the main tasks of O-ring seals, which are positioned at the bottom of the spark plug well, is to keep oil away from the spark plugs.

If the O-ring seal is cracked, worn out, or simply not functioning properly, the oil may leak through the valves and onto your spark plugs. An engine misfire is frequently caused by a leaking O-ring, which, if not corrected, can result in costly engine problems.

These seals are one of the most typical failure areas, and hence one of the chief reasons for oil on spark plugs, thus drivers should check them frequently.

3. Head gasket blown

A burst head gasket is a more significant problem than many drivers realize, and it can cause a variety of engine problems in addition to enabling oil to leak into the spark plugs.

By binding the cylinder head to the engine block, the head gasket aids in the formation of the combustion chamber’s top. As a result, if the head gasket fails, oil can easily leak into the combustion chamber.

Because problems with the head gasket can cost a fortune to correct, it’s critical to catch the problem early so that it can be fixed for less money.

4. Valve guides that are worn or leaking

When the engine is running, valve guides ensure that the valves are always in the correct position, regulating the air intake into the combustion chamber.

When the valve guides degrade or leak, the spark plugs are more likely to end up with oil on them because they enable the oil to leak through.

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In most modern automobiles, spark plugs will be positioned between the intake and exhaust valves. As a result, if oil can leak through the valves, some of it is bound to end up on the spark plugs.

5. Piston compression rings that have been damaged

Damage to the compression rings, in addition to a damaged piston, might cause oil on your spark plugs due to engine oil leakage. Both the top and bottom of the engine will have compression rings, which will keep the engine oil from seeping into the combustion chamber.

These rings are also in charge of removing any excess oil from the cylinder walls, ensuring that no extra oil can get into the combustion chamber. Nothing will stop oil from seeping past the pistons and into the combustion chamber, where some of it will end up on the spark plugs if the compression rings fail or are broken.

6. Piston is broken

Another common reason for oil on the spark plugs is a fractured or shattered piston. As the piston gets hot during regular operation, the heat might sometimes reach too high, causing cracks. Because the flaws in the piston might allow oil to flow through and into the combustion chamber, it frequently ends up on the spark plugs.

Engine misfire, rattling noises while the car is driving, and considerable power loss are all signs of a damaged piston. If you don’t replace a broken piston right away, it could cause irreversible harm to your vehicle. Furthermore, the longer you linger, the more money you’ll have to pay to fix the piston problem.

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Oil on Spark Plugs: How to Avoid It

Here are some useful tips that can help to preserve the spark plugs from oil:

  1. You should change the O-ring seals and gaskets on a regular basis.
  2. Maintain a regular maintenance schedule that includes a thorough car inspection and servicing.
  3. On your engine, don’t use second-hand replacement parts.
  4. Good driving habits and a thorough understanding of your car will aid in both preventing and diagnosing the problem.


Oil on spark plugs is a typical car problem, and while it can have a negative impact on the vehicle’s overall performance, it does not always necessitate a complete engine repair. When you believe that you have oil in your spark plugs, the first thing you should do is inspect the engine to make sure you don’t have another issue with identical symptoms.

Understanding the problem’s causes is also important since it will make it easier to avoid it from happening again. With these causes in mind, and the signs to look for, it should be simple to diagnose and correct the problem before it leads to more significant engine issues.