First of all, a spark plug covered in oil does not mean the end of the world. You may have been told that it can cause the engine to explode, especially if you will not get a good mechanic to fix it but it’s not something that should cause a panic. I did it and I’m pretty sure you can do it too, fix your oily spark plugs and get the engine running like new.

Did you know what a spark plug is in the first place? This electrical device causes the compressed aerosol gasoline to ignite in certain internal combustion engines through an electric spark. Spark plugs are important because they release heat from the combustion chamber and ignite fuel/air mixture.

A spark plug transmits electrical energy when it causes ignition of the air and gasoline mixture. Spark plugs are created with an insulated electrode at the center connected to a magneto circuit or ignition coil on the outside via a heavily insulated wire. Its cylinder has a spark gap inside and its base has a grounded terminal.

There are two kinds of combustion engines. Diesel engines or compression-ignition engines work by compressing the air to start auto-ignition as they inject diesel fuel in the compressed air mixture at high temperatures. Such type may improve their cold start characteristics by utilizing glow plugs. The other type, spark-ignition engines, begins combustion via the spark plugs. The latter works by pulling thermal energy to the cooling system from the combustion chamber and by pulling out the heat from the combustion chamber.

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Spark Plugs Remove Heat from the Combustion Chamber

The spark plugs serve as a heat exchanger. They transfer heat to the cooling system of the engine by pulling the combustion chamber’s unwanted thermal energy. These plugs are not capable of creating heat but they can get rid of it. The firing end of the plugs must be maintained at the right temperature enough to prevent fouling and pre-ignition. The spark plug's range of heat is determined by how it can disintegrate heat from its tip.

Spark Plugs Ignite the Fuel and Air Mixture

The spark plug transmits electrical energy when it is supplied with a voltage high enough to jump the plugs firing end’s gap. The electrical spark causes the ignition of the air and gasoline mixture in the combustion chamber.

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The engine’s performance will greatly suffer from a spark plug covered in oil. If not properly mended, it could lead to blue exhaust, more oil consumption, misfires, and in worst cases, it could start a fire in your engine. Why think about the worst-case scenario when you can fix the problem before it gets that bad?

If you will refer the problem to a mechanic, the first things you’d be told when you ask – what does oil on spark plugs mean, is that it’s a fairly serious problem that needs to be fixed immediately. It can be caused by a variety of factors, such as worn valve guides, failing piston, failing O-ring or gasket.

I am not telling you to forget about having your engine checked by a professional mechanic. You should, every once in a while, to get a complete haul up. The problem with oil on spark plugs though can be fairly simple if you will take the time to learn more about its causes, symptoms, and ways to fix the problem.

Here are the most common reasons why oil leaks into spark plugs:

1. Worn Valve Guides

Valve guides keep the valves in place when the engine is activated. In doing so, they help in regulating the air intake in the engine. Through continued use, these valve guides become too used that they fail with their task. This is the time when you would know that you have to replace your valve guides.

Continue using an engine with worn valve guides may cause more serious problems so you have to repair them or get them done on your own if you can. You will know that your valve guides are failing when there is ash, blue smoke or oil in the wells of the spark plugs.

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2. Failing Piston

This is one of the most common causes of oil on spark plugs wells that should make you want to call a pro if you don’t have an experience on how to fix it. You will know that the engine’s piston is failing when there’s a misfiring, loss of power or excessive oil burning, and knocking or rattle noises while the engine is running. If the engine will continue to run under this condition, the piston may develop a crack or hole due to its high temperature.

3. Failing Piston Compression Rings

You’ll find the compression rings both at the top and bottom part of your engine’s piston. They are positioned in grooves and work by preventing oil from coming in contact with the combustion chamber and helping in removing excess oil found in the cylinder walls. The spark plug wells accumulate oil when the piston compression rings fail. When you encounter this problem, you’d likely smell something oily in the engine or it will have increased blue exhaust.

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4. Failing O-Ring Seals

At the bottom of the spark plug wells, you’ll find the O-Ring seals. The oil will leak beyond the seals when they get worn out and start failing. The oil can get into the spark plug well and causes oil leaks into spark plugs. This requires repair of the spark plug as well as the O-ring seals.

The metal part located on top of the engine is called the valve cover. It works by preventing oil leaks and sealing the engine. The gaskets become brittle over time due to the high temperature it often gets when the engine’s running. This can cause leakage in which the oil can get into the spark plug wells.

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The Common Symptoms of Oil on Spark Plugs

Here are some of the most oil on spark plugs symptoms that can help you in detecting a problem is brewing in your engine so that you can fix it before it gets out of hand:

1. Possible misfires in the engine.

These misfires are brought about by the affectation in combustion energy. This symptom is more noticeable when the engine is running and when it’s on a difficult driving condition.

2. Poor fuel economy

Be alert of how much oil your engine typically consumes under normal circumstances. This will make it easier to notice when the engine begins to consume more fuel than usual.

3. Blue smoke coming out of the tailpipe

You will notice the problem upon inspection of the exhaust fumes. Blue smoke coming out of the exhaust is a clear indication that the engine has a problem that has to be looked at and fixed as soon as possible to prevent it from incurring further damages.

4. The smell of gas coming from the exhaust pipe

Another indication of the problem is the weird smell coming from the pipe, which means bad combustion. There are also instances when you will notice a mix of gasoline and oil coming out of the tailpipe.

5. Back-fire

Mini explosions come from the high energy charge in the exhaust pipe unleashing outside. This happens because the fuel particles no longer burn in the combustion chamber as usual. They go into the exhaust pipe instead and come out as mini-explosions or back-fire.

6. Poor engine performance

After driving your vehicle for a time, you will observe how the engine typically works under normal circumstances. This will make it easier for you to detect when it is starting to act out and giving you a poor performance.

You shall know The Symptoms of Failing Spark Plugs.

Easy Ways to Diagnose and Fix oil on spark plug threads

Whatever your vehicle is if you want to be certain if there is oil on spark plug threads, start the engine and keep it running for a brief period. Shut the engine off and allow it to cool. Make sure that you are equipped with the right tools, including protective gloves, before trying to fix the oil in spark plug chamber.

This will ensure that the engine is okay, especially if you don’t observe misfires or sputtering. If there is still oil on spark plug threads, your problem lies in the O-ring seals and valve cover gasket.

Check if the Valve Cover Gasket Needs to Be Replaced

You will know if the valve cover gasket is causing oil on spark plug threads when you notice a burning smell of oil when you start or drive your vehicle. It is also likely to lose oil faster than usual since the engine is consuming too much oil. Other symptoms include a bad performance of the engine or misfire, dirty state of the valve cover gasket, and when there is oil on spark plug threads.

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1. Prepare Your Tools

To solve the problem by replacing the valve cover gasket, you will need a brake cleaner to wipe out dirt from the valve cover, a flathead screwdriver, high-temperature engine sealant, basic socket set, and ratchet new O-ring seals, and a new valve cover gasket.

2. Remove the Valve Cover

The process of removal depends on the engine type. In certain models, you can easily remove the large nuts found on the holes of the spark plug. In some models, you have to remove the bolts surrounding the valve cover.

On top of the valve cover, you have to carefully remove the ignition coils, high tension wires or spark plug wires. Disconnect the wiring harnesses or any hoses on the cover before you make the bolts loose enough to remove them. Lift the valve cover using a flathead screwdriver, then discard the problematic seals.

3. Wipe the Valve Cover’s Underside until Clean

Clean the oil and dirt, which have accumulated on the valve cover’s underside. Lightly spray with a brake cleaner and wipe using a clean cloth or towel.

4. Put the New Valve Cover Gasket

Install the new valve cover gasket and put the engine sealant at its sides. Leave to dry for 20 minutes. The sealant will help in preventing oil leaks and it will prevent the valve cover from moving as you put it on to the cylinder head.

5. Put Back the Valve Cover Gasket on the Engine

Put the engine’s valve cover gasket, reinstall the bolts and make sure that they are tight enough.

6. Place the New Spark Plug Seals

Put a little amount of the sealant beneath the new plug seals before putting them on the spark plug tubes. Install the spark plug nuts. Make them tight using your hand and make them tighter using the socket and ratchet set.

You can now reinstall the spark plug hoses and wires. Clean oil stains and spills around the engine using a brake cleaner. Get the engine warmed up for about 10 minutes. Check if the oil needs to be changed as per the manual to prevent sludge and crud. 

Is oil on spark plugs bad?

It depends. It is bound to happen as the parts of the engine get rusty but the problem can get worse if you will not do anything fast to fix the issue. Don’t worry, I also start as a novice with only a little clue about everything found in the engine. Your skills in detecting the symptoms of oil on spark plugs and the right ways to get it fixed will become better through continued practice.

While you can always call a pro to get your engine revving up like new, having the basic skills about engine and spark plugs repair will save you a lot of money and time.