Spark plugs are fouled with oil. Causes and solutions

A spark plug is a small but essential component in an engine’s internal combustion as it’s responsible for the source of ignition. It produces an electrical spark igniting the fuel/air mixture inside the engine’s internal combustion chamber. In other words, its spark plug ignites the car’s engine by putting the engine’s pistons into motion. 

Spark plug powers and keeps the car’s engine powered by continuously burning the compressed mixture of air and fuel in the combustion chamber.

It has the ability to withstand extreme temperatures, and besides, these components have the ability to burn off the fuel additives and all contaminants deposits.

Although spark plug is the main component because, without it, your vehicle neither ignites nor moves anywhere, it sometimes gets issues.

Noticing a bad spark plug is simple as your engine may lower its performance, misfire when accelerating, and even have problems with cold-starting. In addition, a spark plug with issues will affect the fuel economy where the car will use much fuel. 

One common issue that affects spark plugs is oil fouling, a problem that occurs due to oil entering the combustion chamber. When spark plugs are fouled with oil, the ignition ability is affected. The oil elements are deposited on the plug’s surface, causing a cover that prevents the spark plug from arcing.

The common causes of spark plugs fouling is head gasket leaking, damaged seal valve guide, rich fuel mixture, and piston rings or cylinders having worn out.

During this situation, the spark plug is forced to take a short path when grounding through the oil. But why are spark plugs fouled with oil?

Here are common causes why spark plugs are fouled with oil:

1. Damage/worn cylinders or piston rings

If the cylinders or piston rings have broken or worn, they will allow oil to enter the combustion chamber, fouling the spark plugs. 

2. Bad or worn valve guide seals

Valve guides play an essential role in providing a tight seal. If the valve guide has developed a fault, the oil can penetrate the combustion chamber through the valve stem. Once the oil enters the combustion chamber, black-like wet oil contaminants will form and get deposited on the spark plugs.

3. Leaks from a damaged head gasket

The Head gasket is very important in your car, and it functions as a seal preventing the coolants from entering the combustion chamber by providing a tight seal.

When the head gasket loses its seal power, the coolant can seep into the ignition chamber, producing wet, oily deposits to the spark plug. If the head gasket is getting a leak, it will not be good news as repairing or replacing the head gasket is costly.

4. A rich fuel mixture

If you find heavy dry carbon deposits on the spark plugs, the likely cause could be the fuel mixture being too rich. The rich fuel mixture results from much pressure on the fuel, which may have been led by plugged fuel return lines or fuel pressure regulator deactivation. When the fuel pressure regulator has faults, it will allow much oxygen in, making the mixture rich.

5. Clogged oil system ventilation

The spark plugs are fouled with oil when the cause is a fault related to the condition of the oil system. There are only two possibilities here:

  • The oil level is exceeded
  • The level is exceeded due to a malfunction that requires dismantling the oil vent system

Solutions for oil-fouled spark plugs?

Of course, you can’t keep your car in this bad condition. A fouled spark plug means your car doesn’t do anything, the car won’t start nor go anywhere.

To resolve issues affecting the spark plug, you, first of all, need to find out where the problem is coming from and the cause. With the common cause of spark plugs fouling, here are the possible solutions:

1. Replace or repair flawed, damaged, or worn cylinder walls and piston rings.

You can do this if the cause of oil entering the combustion chamber is damaged piston rings or cylinders.

3. Replace valve guides

If the oil enters the combustion chamber through a fault valve guide, replace it with a new one. A good valve guide should provide a tight seal that won’t allow any oil to reach the internal combustion part of the car engine.

4. Repair or replace the bad or leaky head gasket

Although very expensive, working on a bad head gasket is essential as it works its role by preventing coolant from entering the combustion chamber.

A cheap way to repair a leaky head gasket is by fixing a head gasket sealer or cooling unit sealer bottle on the cooling system.

5. Check the oxugen sensor, plugged fuel return line and the fuel pressure regulator

When the spark plug shows signs of heavy dry carbon fouling, it indicates the fuel mixture is rich. The fuel mixture becomes rich when there is much supply of oxygen to less fuel.

In such situations, the fault is always oxygen sensor failure, plugged fuel return line, and deactivated fuel pressure regulator. If there is incorrect jetting, a leaky fuel inlet needle valve, incorrect setting of float, the spark plug will experience fouling.

Should spark plugs be covered in oil?

Oil is an essential lubricating agent for the engine components while running. Insufficient oil will lead to overheating due to friction from the moving parts that rub against each other.

However, spark plugs should not be covered with oil. If you find oil on the spark plugs, then it means that there is a problem that needs immediate inspection.

It can be faulty valve cover gaskets, a faulty head gasket, broken piston ring, worn-out valve guides, or spark plug. Moreover, oil in the spark plug can mean that gasoline is mixed with oil.

What happens if oil gets on spark plugs?

If oil gets into the spark plugs, it can affect the engine’s performance and increase oil consumption, causing blue smoke from the exhaust, and misfires.

In severe cases, oil finding its way to the spark plugs can result in an engine fire. So, if your car shows these symptoms, it needs to be inspected right away. 

Can oil on spark plugs cause no start?

Yes, oil on the spark plugs can cause the car not to start. When oil gets to the spark plug, it means that the oil might have shorted out all the plug wires and coils leading to the engine not starting.

If oil is getting in the galley from a leaking valve cover, the valve cover gasket needs to be replaced. Also, you will need to replace the spark plugs as well after removing oil from the galley. 

Can bad spark plugs cause oil burning?

No, the two are not related. Bad spark plugs make the engine run rough due to poor burning of oil. The spark plugs will be fouled by oil hence turning on the check engine light.

So, excessive oil in the exhaust can make the catalytic converter fail or overheat. Oil burning is caused by worn valve stems, piston rings, seals, and guides.


Fouled spark plugs can indicate many issues with engine health. If the engine’s combustion chamber has problems such as oil seeping in, you may know it through the spark plug when it develops fouling issues.

For your car’s safety and great performance, you need to diagnose and fix the issue to avoid greater damage and costly repairs later.

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