Oil is critical in the engine for lubrication. It helps keep the moving parts from friction and excessive heat.
Oil, water, and fuel are three vital engine components that should not mix. The moment this happens you can start experiencing misfires and further engine damage.
Oil can leak to the combustion chambers where the spark plugs are located through a faulty piston, gasket, or worn-out valves.
Causes of oil on spark plugs
There are several different causes why you may find oil on your spark plugs. Here are the most common causes.
1. Faulty/Clogged Crankcase Ventilation
The most common cause when it comes to oil on the spark plugs is that the faulty crankcase ventilation is clogged or faulty. This creates an overpressure inside the crankcase, which forces oil to be pressed into the combustion chamber.
2. Faulty turbocharger
A faulty turbocharger is also pretty common when it comes to oil on spark plugs. When the oil is leaking from the turbo inlet compressor, it goes through the combustion chamber and gets stuck on the spark plug.
3. Leaking valve cover gaskets
If you find Oil on top of the spark plugs, but not in the combustion chamber – check this out!!
In an internal combustion engine, the oil and fuel should never mix. The gasket is a metal piece found on top of the engine that ensures that this does not happen.
However, the gasket becomes brittle due to the high temperatures in the engine block. This can cause oil leaks to reach the spark plugs. You should immediately replace the gasket when this happens.
4. Faulty piston compression rings
A closer observation of piston rings will reveal compression rings at the top and bottom. As the piston moves up and down along the wall these rings will collect oil.
The rings prevent the oil beneath the pistons from reaching the combustion chambers. However, the rings wear out and oil finds its way to the spark plugs. This can cause oil from reaching the moving parts.
5. Faulty pistons
Oil can also leak to the spark plugs through a faulty piston. Pistons operate at high speeds and they are subject to wear and tear. When your pistons are not functioning as they are supposed to, you will hear a rattling noise coming from the engine. If the oil finds its way to the combustion chamber you will have misfires.
6. Worn out valve guides
Valve guides play a vital role in the combustion chamber by regulating the inflow of air and fuel while controlling the outflow of exhaust gases. Fuel, oil, and coolant should not mix at any time in the engine. Valves wear out and oil can find itself in the combustion chamber.
The first symptoms for this are your car emitting blue smoke. You should have the valves fixed as soon as possible to prevent further engine trouble.
Engine misfires
One of the most visible signs of a faulty spark plug is when you notice that your engine is misfiring. In this instance, there is not enough charge to the plugs to promote ignition.
The engine may also produce sputtering sounds and increase carbon emissions. You should have your spark plugs checked immediately to avoid further engine trouble or spending more on fuel.
How to fix oil on spark plugs
The first thing you should check when it comes to oil on the spark plugs is if the crankcase ventilation is clogged. Remove the oil cap when the engine is running on idle. You should find a slightly over or under pressure. If you have a very high pressure you might have clogged crankcase ventilation or bad piston rings.
Check your inlet pipes if you can find a lot of oil there. If its a lot of oil there and your car is equipped with a turbo, you might have a leaking turbo. Check the shaft of the turbo to make sure it’s not lose or damaged.
If you find oil on top of the spark plugs, but not under in the combustion chamber you should check your valve cover gasket.
Symptoms of failing spark plugs
There are some different symptoms you can get from failing spark plugs. Here are them.
Engine misfires
One of the most visible signs of a faulty spark plug is when you notice that your engine is misfiring. In this instance, there is not enough charge to the plugs to promote ignition.
The engine may also produce sputtering sounds and increase carbon emissions. You should have your spark plugs checked immediately to avoid further engine trouble or spending more on fuel.
You can find out more symptoms of failing spark plugs here.
Conclusion
The internal combustion engine uses the gasket to prevent the mixture of oil and fuel. However, the O-rings can become defective or the gasket starts leaking and you have oil sipping through to the spark plugs.
This will cause your car to produce blue smoke as the oil finds its way to the combustion chamber. You should have your plugs checked and the gasket replaced to prevent further engine trouble.
Magnus Sellén
Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.