6 Causes of Oil on Spark Plug Threads
You may have been doing routine maintenance and discovered oil on the threads of your spark plugs. Or maybe you were searching for the cause of a low oil level in your car and found that your spark plugs were covered in oil.
Anyway, now that you’ve found it, you probably have a few questions. Should I be leaking oil into my spark plug wells? Is this a big deal? What could be causing it? We’ll answer all of these questions here, and spoiler alert: this is not normal. This needs to be fixed as soon as possible.
Why Do Spark Plugs Have Oil?
If you find oil on your spark plugs, find out why it’s there. It’s not that your spark plug gasket is leaking, but what could be going on? Here are the most common reasons why you might have oil on your spark plugs:
1) Leaking O-ring seals
Even though spark plugs don’t have gaskets, they still have O-rings. These O-rings keep the oil and everything else on one side of the spark plug and keep the other side dry.
If your spark plugs only have oil on them, you may have a leaking O-ring seal. This is one of the best results you can get from oiling your spark plugs. However, you should get the problem fixed as soon as possible. Leaking O-ring seals can cause your engine to misfire and cause serious damage.
2) Blown Head Gasket
Most people think of a blown head gasket as coolant in the compression chamber, but another liquid that may be leaking is oil. When this happens, oil often ends up pooling in the combustion chamber.
You may notice excess smoke and oil in the coolant reservoir, and even oil on the top of the spark plugs. You need to replace your head gasket before the problem gets worse and leads to more serious issues. The good news is that head gaskets are cheap, but the bad news is that it’s a labor-intensive process.
3) Worn/Leaking Valve Guides
Valve guides keep the intake and exhaust valves in the correct position at all times. In addition, they have seals that prevent oil from getting into the combustion chamber. If these seals fail, it’s a stone’s throw away for oil to get into the combustion chamber and reach the spark plug seals.
Like any other component, the valve guides themselves aren’t that expensive, but replacing them takes a lot of effort and time, which can result in a costly repair shop bill.
4) Leaking valve cover gasket
Vehicles use valve cover gaskets to keep oil close to components that need it and away from components that don’t. One component that keeps oil away is the spark plugs. However, if the valve cover gasket leaks, it can easily allow oil to get inside the spark plugs. Like head gaskets, valve cover gaskets are inexpensive but labor intensive to replace.
5) Damaged piston compression rings
There is a compression ring around each piston in your engine that prevents oil from seeping into the combustion chamber. But when these compression rings get damaged, oil can’t get into the combustion chamber.
These rings keep everything running smoothly and prevent major problems, so if you suspect damage to your compression rings, it’s best to have them repaired as soon as possible.
6) Piston Damage
Damaged or cracked pistons are rare, but not impossible. The combustion chamber can get very hot, and as pistons get older, this heat can become excessive. If a piston cracks, you will have to rebuild your engine, which is never a cheap expense.
However, ignoring the problem could leave you stranded on the side of the road and with a completely destroyed engine.