Oil on Spark Plug Threads, what’s the cause and its effect? For a car engine to run smoothly, oil is needed, though, there are places the oil shouldn’t get to. For instance, oil should not be found on Spark Plug Threads. If you find oil there it signifies that there’s an issue with a component of the engine. But, what could be the cause? You will find out as you continue to read.

Oil on Spark Plug Threads

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Oil on Spark Plug Threads

Oil on your spark plug threads can be caused by several possible issues. They are;

  • Leaky O-rings
  • A broken valve cover gasket or head gasket
  • A broken piston or faulty piston compression rings
  • worn-out valve guides

However, regardless of the reason, when you find oil on spark plug threads, you need to inspect it to find the exact cause and replace faulty components to restore your engine to its optimal operation.

What are Spark Plug Functions?

The spark plug’s function is to ignite the air and fuel mixture to create energy-generating combustion in your engine. Thus, the combustion procedure requires strict precision from each component of the engine, including ignition at precise moments in time for optimal combustion.

However, the spark plugs ensure this by maintaining the right temperature in the engine’s combustion chamber. Despite being a small component, faulty spark plugs heavily affect your engine performance, and oil on spark plug threads is a common issue you shouldn’t ignore.

What will happen if there is Oil on the Spark Plugs?

With the way the combustion system is designed, air and fuel are the only two things that should come into contact with your spark plugs. And, when everything is in working order, there shouldn’t be any oil on your spark plugs.

Should in case oil finds its way to the spark plugs, an oil-soaked spark plug might not be able to make a spark effectively or at all. This means suboptimal or worse, no ignition, no combustion, and no energy generation.

Normally, an oily spark plug directly affects engine performance and if not taken care of asap, it can prematurely wear out the engine bearings, because too much fuel is piling up in the oil pan.

Why is there Oil on My Spark Plug Threads?

Below are some of the reasons you find oil on Spark Plug threads, and how to fix it.

  • Excess Oil

Spark plugs are components of your engine. If you apply too much oil to your engine, it can leak out and cover your spark plugs, leaving them fouled. Fouled spark plugs have their own set of signs, such as reduced gas mileage, engine misfiring and rough idling, and reduced engine power.

How To Fix It?

There are two ways you can take out excess oil from your engine.

Drain Plug: open the drain plug on your engine’s oil pan and let the excess oil drain out. Though you’ll have to raise your car up in order to access the oil pan.

Using an Oil Extractor Pump: use an oil extractor pump to remove the excess oil. Oil extractor pumps let you remove excess oil through either the dipstick tube or the oil cap.

  • Leaky ORings

The spark plugs are sealed in place through the use of O-rings, designed to prevent oil and other undesirable substances from reaching the parts of the spark plug where they aren’t supposed to be.  So leaky O-rings can cause oil to flow to the spark plugs.

How To Fix It?

Is very easy to fix a leaky O-ring. And it’s an inexpensive fix. All you’ll need is to get a replacement O-ring and a tool you can use for prying, like a small crowbar or a flathead screwdriver.

Remember to install the O-rings the right way around inside their holes. And also ensure you install them with the tapers pointing towards the engine so that they can easily slip over the spark plugs.

  • Broken Valve Cover Gasket

There are different gaskets in an engine, with one of the most important ones being the valve cover gasket. This gasket is located in between the valve cover and the top of the cylinder head and is used to create a seal between these two components of the engine.

However, the valve cover gasket is likely made out of rubber or silicone, which makes it more likely to fail due to old age or high temperatures. So, if your valve cover gasket is leaking; you’ll likely see oil dripping from under the valve cover.

How To  Fix It?

Fixing a broken valve cover gasket is pretty cheap, especially if you do it yourself. Start by taking out the valve cover. The valve cover gasket will be a strip of rubber that runs along the edge of the valve cover.

When the valve cover is off, you can take out the old gasket by simply pulling it off the cover. Then, you can install the new one.

  • Broken Head Gasket

The head gasket is an important component of the car. It’s located between the bottom of the cylinder head and the engine block. Its function is to maintain a seal between these two parts. By allowing oil and coolant to circulate through the engine without leaking out and also keeping the combustion chamber airtight.

However, the head gasket in modern cars is usually made from a combination of steel and elastomer, which is a type of rubber. Modern head gaskets are more durable than head gaskets from previous decades, but they do occasionally fail, usually as a result of overheating.

How To Fix It?

Take your car to an auto repair shop to have your head gasket fixed, you will likely pay a lot for the repair. This is due to the complicated and time-consuming nature of this repair.


The presence of oil on spark plug threads is an issue that should not be overlooked by car owners. While oil is an essential lubricant for various engine components, it should never find its way to the spark plugs. This occurrence is often indicative of underlying problems within the engine’s components and seals.

Several potential culprits can lead to oil leakage onto spark plug threads, including leaky O-rings, damaged valve cover gaskets, malfunctioning head gaskets, or even excess oil in the engine. Regardless of the specific cause, addressing the issue promptly is crucial to maintaining the optimal performance of your vehicle.

Oil-soaked spark plugs can result in reduced engine efficiency, decreased gas mileage, rough idling, and engine misfires. Moreover, prolonged exposure to oil can lead to premature wear of critical engine components, such as bearings, and result in more extensive and costly repairs.

The key takeaway here is that early diagnosis and swift action are essential when oil is detected on spark plug threads. Identifying the root cause of the issue and taking the necessary steps to rectify it will not only restore your engine’s performance but also extend the longevity of your vehicle.

Regular maintenance, including checking and replacing faulty components, is an investment in the reliability and efficiency of your car, ensuring it continues to run smoothly for years to come.


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