Oil Fouled Spark Plugs (Everything You Need to Know)

Spark plugs play an important role in engines and have been used for many years by car owners. Having a faulty or damaged spark plug is not something that will get noticed immediately but it can cause a lot of damage to your engine components. Therefore having an insight on what to look out for if this happens can help you avoid huge repair bills in the future.

In this article, we will look at what causes oil fouled spark plugs and things you can do to fix and prevent it from damaging your car engine.

What causes an oil-fouled spark plug?

The piston rings need to have a good seal between the top of the piston and the cylinder head. Without a good seal, the oil will pass by it and collect inside the combustion chamber.

The oil is then ignited when the spark plug fires. The oil will then burn and create excess back pressure in the combustion chamber causing the poor acceleration.

This back pressure also burns off gasoline before it can ignite. The lack of power due to this missing explosion is why special fuel systems are installed on cars with a high-performance engine or turbocharged engine (which increases RPMs).

This is very similar to an engine that has carbon build-up on its piston rings. The difference however is the carbon build-up won’t be burning as much and the car will get better gas mileage.

The oil in an oil-fouled spark plug will ignite and burn, causing lower gas mileage. Dry start symptoms: If your car has lately had trouble starting in cold weather then it could be an early sign of a defective piston ring(s). A mechanic should inspect your car to make sure the rings aren’t stuck and that the piston isn’t too scared.

In many cases removing carbon buildup by changing the oil can cure this problem, but if there is a burnt oily smell inside your engine then you definitely have this problem.

What are the signs of an oil fouled spark plug?

Hard starts on cold days when the engine doesn’t warm up, wet-looking exhaust smoke from the exhaust pipe, lack of power.

Another more difficult to diagnose symptom is timing advance being needed for every start-up during winter weather and not being needed in summer or better yet, being needed constantly throughout the year. Noticeable oil and oil smell on the spark plugs when you inspect them as well.

Are oil fouled spark plugs dangerous?

No, the amount of oil that is produced through combustion causes back pressure in the exhaust but does not create enough pressure to blow a hole in an exhaust system. If you are lacking power, however, you should see a mechanic as soon as possible as this could be a sign of severe engine damage due to piston ring wear.

Can Oil ruin spark plugs?

Yes, over time oil can wick or creep its way into the porcelain area of your spark plug and cause it to short out. In this situation, your car would need to be towed in for service.

How often does an oil fouled spark plug happen?

A car’s engine will develop an oil-fouled spark plug with excessive carbon buildup on the piston rings. This buildup happens within about 50k miles (which is considered low mileage for most cars).

Some engines however, can make it to 100k miles before they develop this problem. The more you drive your car and the older it is, the faster this will happen.

A faulty engine design may cause oil to be poured into the combustion chamber because of extra clearance between the piston and cylinder wall. This could be a problem with your timing chains or guides, check this video and see if you have that problem.

How do you stop oil fouling on spark plugs?

The best way to stop oil fouled spark plugs is to change your oil more often. But by the time you have noticed a problem, it has been too late.

You should change your oil every 3,500 miles (or if you drive in extreme conditions like winter weather or off-roading). If you wait too long to change your oil then it will start drying out the oil and the rings won’t seal properly causing an unburned mixture to get into your exhaust system.

There is a product called WYNNS that was designed to clean carbon buildup from engine piston rings. I can’t vouch for it as I haven’t used it myself but you might want to look into that product if you have this problem.

You will also need to replace the valve seals if they are already damaged, make sure that you get OEM Valve seals to help prevent any oils from entering the combustion chamber.

What does an oil-fouled spark plug look like?

An oil-fouled spark plug will appear wet or maybe black with a burnt oily color on top of the plug.

Which cars are more prone to oil-fouled spark plugs than others?

Cars that have a straight thru carburetor: The straight atmospheric side fuel injection takes place and the air/fuel mixture is taken in through a venturi. A blast pipe is attached to the end of the venturi for this purpose.

A carburetor (also called an air meter) is an instrument used in conjunction with an internal combustion engine to mix and deliver fuel for combustion. It works by metering out fuel in proportion to airflow into the cylinders.

The carburetor can be either of the downdraft type or the updraft type. The updraft carburetor is used in some stationary engines, and in nearly all automobiles.

The straight atmospheric side fuel injection takes place and the air/fuel mixture is taken in through a venturi. A blast pipe is attached to the end of the venturi for this purpose.

A carburetor (also called an air meter) is an instrument used in conjunction with an internal combustion engine to mix and deliver fuel for combustion. It works by metering out fuel in proportion to air flow into the cylinders. The carburetor can be either of the downdraft type or the updraft type.

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