Causes of Oil on Spark Plug Threads is reader supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you.

The Role of a Spark Plug

Spark plugs have to be one of the most important components found in the ignition system. The role of a lighter is quite similar to the role of a spark plug, as both are used to initiate combustion. To put its role in some perspective, the lighter is a handy tool that you can control far more easily. But for this spark plug scenario, it is not the same. Just imagine what would be the consequences of taking spark plugs lightly.

If you discover some oil on your spark plug, it is bad news for your engine. But before you start panicking, let me tell you that it can be fixed. Grease on the spark plug or the electrode tip of a spark plug can intervene to produce hot sparks to ignite the fuel. This can lead to a lack of power from the piston cylinder and further result in an engine misfire.

When the oil enters the spark plug, it will drastically affect the engine’s performance. Meanwhile, it will also lead to increased oil consumption. On the extreme side, it might even lead to a serious engine fire. Also, having oil molecules on your spark plug for a long time can potentially destroy your catalytic converter because of all the unburnt fuel.

In most cases, when there is oil on the spark plug, it is caused by bad valve cover gaskets, broken piston rings, plug o-rings, leaking valve cover, and worn spark plugs. Some of the easily detectable symptoms of oil on spark plugs can be blue smoke coming out of the exhaust, engine misfires, and poor fuel economy.

Causes for Oil on Spark Plugs

1) Faulty Valve Cover Gaskets

The key function of the valve cover gaskets is to keep the oil on the cylinder heads and then to keep those cylinders away from the other parts of the engine. However, because of high temperatures in the engine, the valve cover gaskets often wear out while allowing the oil to leak. This oil leakage can reach spark plugs located in the Over Head Valve (OHV). In certain cases of blown head gasket, there is another fluid (a coolant) that leaks out in the compression chamber. When this happens, it is easy for oil to get inside the combustion chamber.

After that, you will notice a lot of smoke, and you will also find some oil on your spark plugs. You should take immediate action by replacing the head gasket before the situation worsens. The good part is that you can easily find head gaskets in the market and they are really cheap. However, the drawback is that it is very time-consuming work.

2) Degraded O-Rings

O-rings are used to keep oil on one side and the dry components on one side. But if you have oil on your spark plug, this can mean that your O-ring’s seal is leaking. As soon as you detect this, you need to address the problem. Otherwise, leaky O-rings can result in engine misfire and greater damage. Again, leaky O-rings are also degraded because of their exposure to heat.

3) Damaged Pistons and Their Compression Rings

Having a broken/cracked piston head is a rare case scenario. However, it is a possibility too. As the engine gets old, it wears out gradually. Since the combustion chambers are extremely hot, this heat can become unbearable for the piston. As a result, they cause cracks on it. Make sure to see a mechanic immediately because your engine needs a complete re-build. Do not let this issue slide because then you are ruining your engine.

Compression rings surround each piston in the engine. They ensure the smooth functioning of the engine and prevent oil from leaking inside the combustion chamber. But if they get damaged, there is nothing that can stop the oil from entering the combustion chamber. As the engine becomes older, it is normal for compression levels to drop, and the oil pan will build up a lot of pressure. So, if the compression ring is impaired, high-pressure oil might enter the combustion chamber.


1. How to get oil out of spark plugs?

If there’s oil in the spark plug wells, you might be wondering what you need to do to get it out. The truth is that it’s more important to find the source of the problem and fix it. Getting oil out of a spark plug is not as simple as just cleaning it one time. Rather, you need to find the source of the problem. It is because the oil is going to find its way inside the compression chamber again and again. This is why it is important to sort out the root problem. For example, if your O-rings are damaged, you need to fix them first, and you are good to go!

But if there is excess oil, you can get a carb cleaner. You can spray this carb cleaner into the plug holes and allow the oil to go back into the combustion chamber.

2. Is it safe to drive with oil on spark plugs?

Yes, you may drive with oil on your spark plugs, but only temporarily. If the problem persists, it is not safe to drive with oil on a spark plug. Avoid using your car until the issue is solved completely.

3. Can we reuse spark plugs?

Yes, once your car has been repaired, there is no harm in using the same spark plugs. Remember, this issue is not about getting oil on spark plugs. It is more about “how” the oil got there. You can use a carb cleaner to spray down all the grease and let it dry. After they dry, you can reuse them.


If any vehicle is giving symptoms of oil on the spark plug, you should examine them right away. Therefore, if there are any oil leakages into the spark plug, it is an indicator of a serious problem. You must take it under consideration and repair it immediately.