What Causes Oil on Spark Plug Threads ?

Oil is very crucial to the proper functioning of a vehicle. However, having oil on spark plug threads is a problem that requires immediate attention. Engine oil and other lubricants are useful when they stay in the place allocated in the vehicle.

So, if you discover oil on your car’s spark plug threads during a routine check or maintenance, don’t panic; however, it is not a license to overlook it, as it can lead to severe engine problems.

Now, let’s look into the issue to find out the causes of oil leaking into spark plug threads and the solution to the problem in the subsequent sections of this article.

What Causes Oil on Spark Plug Threads

Several factors are responsible for oil leaking into a vehicle’s spark plug threads. Some of the causes of oil on a car’s spark plug threads include the following.

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Excess oil in car engine

If you accidentally put too much oil in your vehicle’s engine, the excess will flow out, and some may leak into the spark plug holes. The spark plugs are vital components that enhance a vehicle’s ignition process.

The spark plugs help to ignite the fuel in the cylinder to start the car. Therefore, dirt, debris, or oil will hinder the spark plug’s ability to create a spark between the plug electrodes for ignition.

Meanwhile, oil leaks into the spark plugs will have them fouled. In this case, you will start to experience reduced gas mileage, rough idling, reduced engine power, and engine misfiring. The issue of oil on spark plug threads in Chevy Impala is pretty much similar to oil on spark plug threads in Silverado.

Defective O-Rings

The O-Rings help to seal the spark plugs area to prevent the entrance of oil and other unwanted substances. The O-Rings are usually found within the area of the valve cover; however, the O-Rings may be separate from the vehicle’s valve cover, depending on the car’s make or model.

On the other hand, the O-Rings may be attached permanently to the valve cover. In any case, since the O-Rings are made of silicone or rubber, they can wear out by degradation over time.

High temperature can affect the O-Rings, resulting in damage, which in turn leads to oil leaking through the O-Rings into the spark plugs area.

Defective valve cover gasket

The valve cover gasket is one of the most important among the several gaskets in a vehicle. This component sits between the top of the vehicle’s cylinder head and the valve cover, thereby creating a seal between them.

The valve cover gasket ensures that oil pumped into the cylinder head to be redirected to the camshaft, valve springs, valve guides, etc., go into the appropriate place.

However, the valve cover gasket is also made of silicone or rubber; it wears out due to heat or aging. This defection will cause the component to malfunction and allow oil to leak into the spark plug area.

Bad head gasket

A vehicle’s head gasket is the most vital gasket among others. The head gasket is positioned in between the vehicle’s engine block and the bottom area of the cylinder head.

The head gasket keeps the seal between the engine block and the cylinder head, allowing oil and coolant to flow in the correct direction without any leaks. They are made of a superior kind of rubber – elastomer and steel.

However, the component can fail over time, resulting in oil leaks into the spark plugs and other areas in the engine compartment.

Cracked piston

A vehicle’s pistons are responsible for assisting the engine in turning combustion into rotational power. The pistons are located up in the engine combustion chamber, hence their exposure to lots of heat.

Therefore, if the pistons suffer from too much heat, they may crack in the long run. When this happens, it will allow oil into the combustion chamber where the pistons sit and eventually allow oil to reach the spark plugs.

Bad valve guides

The valve guides are responsible for ensuring that the valves align with their valve seats. They also protect the valve stems from wearing out.

If the valve guides become broken or wear out, they can no longer create a perfect seal within the engine’s combustion chamber. When this happens, worn-out valve guides will create a vacuum, allowing oil to leak into the spark plug threads.

What Do You Do If You Have Oil In Your Spark Plugs?

Oil and other substances like dirt or debris affect the proper functioning of the spark plugs. However, if you have oil on spark plug threads only, kindly do the following to resolve the issue.

  • Remove and clean the spark plugs.
  • Spray some carburetor cleaner into the hole of the spark plugs
  • Allow the oil to flow into the combustion chamber while the leftover oil dries up later.
  • Reinstall the cleaned spark plugs

Note that oil on spark plug threads in LS1 engines is likely to project the same problems as oil on spark plug threads in LS3. Hence, you can fix the spark plugs issue in both engines with similar strategies.

How Do You Fix Oil On Spark Plug Threads?

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. Referring back to the causes of oil leaks into a vehicle’s spark plugs area as outlined above, the following solutions will help fix the problem.

Remove excess oil

If the issue is traceable to excess oil in the vehicle’s engine, you will have to drain out the excess. There are two different ways to handle the oil removal; firstly, locate and open the drain plug on the engine’s oil pan to allow the excess oil to flow out.

However, you will have to raise the car to locate the oil pan. On the other hand, get an oil extractor pump and use it to remove the excess oil through the oil cap or dipstick.

Replace defective O-Rings

Once you identify that one or more O-Rings are bad, kindly get a replacement as soon as possible. Ensure to remove the old O-Rings by taking off the valve cover to allow the O-Rings to come off. Then pry them out through the valve cover’s underside.

After that, fix the new O-Rings by sliding them in place. Coating the O-rings with a thin oil layer before sliding them in will lubricate and make them sit properly. Meanwhile, ensure to fix the O-Rings correctly with the tapers pointed directly towards the engine.

Replace the defective valve cover gasket

Again, if you notice that a defective valve cover gasket is the issue, kindly get a new replacement for the component. In order to fix the new gasket, remove the valve cover and take off the valve cover gasket. It is usually a rubber strip that runs along the valve cover edges.

Once you remove the old valve cover gasket, install the new one carefully. Meanwhile, you must ensure that you buy the recommended valve cover gasket for your car. After installing the valve cover gasket, fix the valve cover back in place.

Replace the head gasket

The head gasket is a complicated component that only professional auto mechanics can fix. If you intend to fix the component by yourself, ensure to be extremely careful. However, kindly buy the part and allow an expert to do the job to be on the safer side.

Replace the cracked piston

If you have a cracked or broken piston that results in oil leaks into the spark plugs area, kindly replace the component. You will need a dead blow hammer, as well as a piston ring compressor to do this job.

However, if you’re not sure about fixing the component perfectly, kindly contact a professional auto mechanic to do the job.

Replace the valve guides

Replacing a vehicle’s valve guides is pretty tough. First, you need to disassemble the engine to access the old valve guides in the vehicle’s cylinder head.

Once you identify the valve guides, use a valve guides removal tool to remove the old ones and install the new valve guides. Ensure to use a valve driver to push the component in place perfectly. After that, you can reassemble the engine.

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Frequently Asked Questions – FAQs

Q: Should there be oil on spark plug threads?

If you’re asking, “Do you put oil on spark plug threads?” Of course not! When you have oil on your car’s spark plug threads, it can lead to engine damage.

The spark plug threads were not designed to accommodate oil; hence, it can be detrimental to the spark plugs and the vehicle’s engine at large.

However, if you have some oil in your vehicle’s spark plug threads, do not panic. It is usually due to oil leaks from a bad gasket or seal.

In that case, kindly replace your vehicle’s gaskets and seals as soon as possible. You will save your vehicle’s engine from imminent damage when you replace those parts quickly after detecting the oil leaks.

Q: Why are my spark plugs full of oil?

Your vehicle’s spark plugs are full of oil because the O-ring, which is responsible for sealing the well to protect it from oil and dirt, has deteriorated. When this happens, you can partially resolve the issue by tightening the bolts on the valve cover.

However, the guaranteed solution to oil leaking into a vehicle’s spark plugs is to replace the valve cover gasket alongside the seals. This will resolve the problem once and for all.

Meanwhile, ensure to verify if the problem will require a complete replacement of the valve cover gasket and the seals before doing so. Meanwhile, note that oil on spark plug threads in a motorcycle depicts virtually similar symptoms to that of a vehicle.

Q: Can oil ruin a coil pack?

Oil may not directly ruin a coil pack because the ignition is situated in a housing filled with oil. However, an oil leak can ruin a coil pack if the coil overheats and the housing breaks. Oil leakage can result in a severe ignition coil problem.

If you suspect any oil leaks around your car’s ignition coil housing, endeavor to contact a professional auto mechanic as soon as possible. Meanwhile, it is important to replace the defective coil immediately before it fails completely. Remember, prevention is better than cure.

Q: Can oil in spark plugs cause no start?

Of course, you will find it hard to start your car if oil gets in the spark plugs. If oil enters your vehicle’s spark plugs, it will eventually affect the spark plug wires and ignition coil. When this happens, the car’s engine will not start. Unfortunately, this is a common symptom of oil on spark plugs.

Therefore, if you discover that oil has found its way into your car’s spark plugs, it is a sign that the valve cover gasket is bad. The best solution is to replace the valve cover gasket as soon as possible to prevent the problem from escalating.

Q: Can you spray wd40 in a spark plug hole?

No, you shouldn’t spray WD40 in your car’s spark plug hole. WD40 is not an ideal lubricant to use in your car’s spark plug hole because it is a solvent. It has a tendency to wash off the oil on your car’s cylinder walls, resulting in a tough challenge for the engine.

Instead of spraying WD40 in your car’s spark plug hole, it is advisable to spray carburetor cleaner into the hole. 

The carburetor cleaner will help to dissolve tough debris and other unnecessary contents in the spark plug hole. After that, you can blow in compressed air to get the debris or dirt out of the spark plug hole.

Q: How much does it cost to fix oil on spark plug threads?

The cost of fixing oil on a car’s spark plug threads varies due to different factors, including the expert auto mechanic fee, location of repair, etc. However, repairing oil on spark plug threads costs around $215 to $261.

Parts may cost around $54 to $57, while labor cost is estimated at around $161 to $203, as the case may be. The cost of fixing oil on a vehicle’s spark plug threads is worth it because the outcome of the problem is a bigger problem if not treated immediately.

Final Words

This article has exposed vital information concerning the causes of oil on spark plug threads and their corresponding solutions. So, you don’t have to worry if you’re experiencing this challenge at the moment.

Kindly ascertain the exact cause of the oil leaks into the spark plugs area and implement the suggested solution above. However, if you’re not sure about performing the task perfectly, ensure to contact an expert auto mechanic to do the job.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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