How to Fix Oil on Spark Plugs

Spark plugs and oil both play important roles in the operation and smooth running of a car’s engine. The two however, should never come into contact but they sometimes do. This introduces a serious problem which could cause irreversible damage to parts of the engine. If caught early, the problem can be easily fixed without any damage to the engine or any of its parts.

Function of Spark Plugs

A spark plug is a small but crucial electrical device fitted into the cylinder head of aninternal combustion engine. Spark plugs have two main functions:

Ignition of air/fuel mixture: Electrical energy transmitted through the spark plug produces that crucial spark which gets the fire burning. The spark created ignites the air/fuel mixture in the combustion chamber which allows you to start your car.

Function of Spark Plugs

The engine’s pistons are set in motion so your car gets powered up and a smooth burn of the air/fuel mixture is maintained. Spark plugs are what can be compared to the strike of a matchstick which starts the process of burning fuel.

Heat dissipation: Another primary function of spark plugs is to remove heat from the combustion chamber. If the plug’s firing end gets too hot, this could cause pre-ignition. It therefore serves as a heat exchanger which pulls thermal energy out of the combustion chamber towards the engine’s cooling system.

A spark plug’s heat range refers to its ability to dissipate heat from the firing tip. Different spark plugs have varying heat ranges. Differences in heat range lie in a spark plug’s ability to remove heat in the range of 70° C to 100°C.

Oil in Spark Plugs

Why is there oil on my spark plugs?This is a common question simply because oil leaks into the spark plug wells is actually quite common. This issue involves spark plugs and oil. We know why spark plugs are important.

Oil is essential to proper working of the engine because it provides lubrication which minimizes friction between moving parts. Moving parts generate a tremendous amount of heat and the oil also helps to dissipate it.Oil is distributed around the engine using an oil pump. It first flows through an oil filter then goes through the engine’s oil passages and through pistons, springs, rings and valve stems.

Needless to say, oil should not get onto spark plugs but sometimes it does. When this happens it means there is an oil leak somewhere. Here are some likely reasons behind such an oil leak.

Leaking Valve Cover Gaskets

Oil in Spark Plugs

The valve cover gasket is a metal part on top of the engine which keeps it sealed to prevent oil leakage. Considering the high temperatures in the engine when the car is moving, it is not surprising that valve cover gaskets get worn out over time. It typically starts by cracking and later shatters. When this happens oil leaks through it.

Worn valve guides

The purpose of valve guides is to manage intake of air into the engine. They secure the valves when the engine is in operation. Like many other parts of the engine, valve guides get worn after continued use. When they do oil leaks onto the spark plugs.

Worn O-Ring Seals

O-ring seals are positioned right under the spark plug wells. When these seals get worn out or damaged, oil easily leaks through and makes its way into the spark plug wells.

Faulty Piston

If the piston is exposed to too much heat, it cracks. When it does, it lets oil leak onto the spark plugs. Aside from leaking oil, a faulty piston also causes knocking and rattling sounds and weakened engine performance.

What Happens If Oil Gets On Spark Plugs?

Even if you are not a professional mechanic, certain signs will point towards an oil leak into spark plug wells.

  • Blue exhaust smoke. This kind of smoke is produced when oil leaks, mixes then burns with fuel.
  • This is felt as a sudden jerk when the engine is running. In this case, it happens when a layer of oil has coated the spark plug.
  • When oil gets into spark plug wells, fuel particles in the combustion chamber don’t burn as they should. They then enter the exhaust pipe highly charged. The energy is released as mini explosions.

How to Fix the Engine Oil Leakage to Spark Plugs

When you have oil leaking into your spark plug wells, it is most likely caused by a leaking valve cover gasket or a worn O-ring seal. You can fix both yourself.

How to Fix the Engine Oil Leakage to Spark Plugs

As a preliminary caution, make sure the ignition is off. Also disable the battery by detaching the negative terminal.

Remove valve covers. Remove all the cover bolts and pull it out. If the cover has adhered to the head as often happens, use a rubber mallet to pull it out. Avoid using a metal tool like a screw driver because this may cause permanent damage to the cylinder head.

Remove the worn gasket and O-ring seal. If it was installed using silicone, it may not come off easily but will come off with some effort.  Discard the two worn out parts.

Clean out the head and valve cover surface. Use plastic tools to clean away any traces of the old gasket that may have been left. Use a degreaser to clean both the valve cover and cylinder head.

Install new gasket. Some engines require use of silicone when installing new gaskets. Check the engine OEM literature to confirm the exact recommendation for yours.


Having oil in your spark plug wells is not one of those problems you notice and wait until it is convenient to fix it. It is actually a very serious problem which should be rectified immediately it is noticed. It can cause damage to the engine such as warped pistons and valves.

If left unchecked for some time, it could cause an engine fire if the plugs ignite the oil. If you don’t know how to fix oil on spark plugs, take your car to a professional mechanic immediately.

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