6 Causes of Oil on Spark Plug Threads (and in Wells)

Maybe you’re completing some routine maintenance and you discovered the oil on your spark plug threads. Or perhaps you were troubleshooting why your vehicle had low oil and discovered that you had spark plugs covered in oil.

Either way, now that you’ve found it, you’re sure to have a few questions. Are you supposed to have oil leaking into the spark plug wells? Is it a big deal and what’s causing it?

We’ll answer all those questions here and – spoiler alert – it’s not normal. You’re going to want to fix it as soon as possible.

See Also: 9 Conditions of Spark Plugs (and What Each Means)

Reasons There’s Oil On Your Spark Plugs

Once you’ve discovered oil on your spark plugs, it’s time to dive into why it’s there. It’s not like there’s a spark plug gasket that’s leaking – so what’s going on? We’ve highlighted the most common reasons there might be oil on your spark plugs below.

#1 – Leaky O-Ring Seal

While your spark plugs might not have a gasket, they do use O-rings. These O-rings keep oil and everything else on one side of the spark plug, and the other side remains dry.

If you only have oil on one spark plug, you might have a leaky O-ring seal. This is one of the best outcomes if you have oil on your spark plugs. However, you still need to address the problem as soon as possible. Leaky O-ring seals can cause your engine to misfire and lead to more extensive damages.

See Also: Spark Plug Socket Sizes

#2 – Blown Head Gasket

While coolant in your compression chamber is what most people associate with a blown head gasket, another fluid that could be leaking is oil. When that happens, it’s common for oil to get into the combustion chamber.

You’ll notice excessive smoke, oil in your coolant reservoir, and there will be some oil on the tip of your spark plugs. You’ll need to replace the head gasket before the problem worsens and leads to more severe concerns. The good news is that head gaskets are cheap – the bad news is that it’s a labor-intensive process.

See Also: Cylinder Head Repair Cost

#3 – Worn/Leaking Valve Guides

Valve guides ensure that your intake and exhaust valves stay in the appropriate position at all times. Not only that, but they have seals that keep oil out of the combustion chamber.

If those seals give out, then oil gets into the combustion chamber, and it’s a quick hop, skip, and jump away from getting on the spark plug gaskets.

Like other components here, valve guides themselves aren’t that expensive, but they require a lot of work and time to replace – which can rack up a massive bill at the repair shop.

See Also: 3 Causes of Oil in an Intake Manifold

#4 – Valve Cover Gasket Leaking

Your vehicle uses valve cover gaskets to keep oil near components that need it and away from those that don’t. One of the components it keeps oil away from are the spark plugs. But if the valve cover gasket is leaking, then oil can easily seep into the spark plugs.

Like head gaskets, valve cover gaskets are cheap but it’s a labor-intensive process to replace them.

#5 – Damaged Piston Compression Rings

Around each piston in your engine, there are compression rings that keep oil from seeping into the combustion chamber. But when these compression rings are damaged, nothing is keeping the oil from seeping into the combustion chamber.

These rings keep everything running smoothly and prevent more significant problems. So, if you suspect damaged compression rings, it’s best to repair them as soon as possible.

#6 – Damaged Piston

While damaged or cracked pistons are rare, it’s not entirely unheard of. Combustion chambers get extremely hot, and as the pistons age, this heat can become too much for them. If you have a cracked piston, you’ll need an engine rebuild, which is not a cheap process.

However, if you let the problem go, you risk breaking down on the side of the road and potentially completely destroying your engine. Cracked or damaged pistons isn’t a problem you can ignore.

Read Also: 6 Causes of Oil Coming Out of a Tailpipe

How to Get Oil Out of Spark Plug Wells

If there’s oil in the spark plug wells, you might be wondering what you need to do to get it out. The truth is that it’s more important to find the source of the problem and fix it.

That’s because the oil will work its way into the compression chamber and burn off. As long as there’s no more oil leaking in, that’s the end of your problem.

So, while oil on your spark plugs is a big deal – it’s not something you need to tear your engine apart to clean. Once you’ve found and repaired the faulty component, you should be good to go.

However, if you are worried about the excess oil, all you need to do is spray some carb cleaner into the spark plug holes and let the oil run into the combustion chamber. Reinstall the spark plugs and let your engine burn off the excessive oil.

See Also: Spark Plug Blow Out (Why It Happens and How to Fix It)

How to Fix: Oil On Spark Plugs

While simply cleaning off excess oil temporarily solves the fouled plug problem, pinpointing and repairing the root cause of the oil leak is necessary or you’ll just be repeating the same cleanup process.

Potential solutions include:

• Replace damaged or worn spark plug tube seals and O-rings allowing engine oil down into the well. Ensure the fresh seals are properly fitted.
• If oil smoke or coolant mixing suggests head gasket failure, replace the complete gasket set to prevent further compression leaks. This extensive engine repair restores the seal between the block and heads.
• For oil-fouled plugs alongside valve train noise, consider replacing worn valve stem seals and guides that have loose tolerances. This also necessitates some valve and cylinder head removal for access.
• Confirm piston, ring and cylinder wall wear as potential sources of oil blow-by internally in the engine, especially on high mileage vehicles. Engine overhaul and rebuild may be required in such cases.

While fouled spark plug replacement and wiring insulation cleaning may get a rough-running engine operational short term, the root sources listed above must get addressed to prevent ongoing oil contamination issues leading to misfire conditions or catalytic converter damage.

Can You Drive With Oil On Your Spark Plugs?

In short, yes, you can drive with oil on your spark plugs, but you’re going to want to figure out how it got there. That’s because oil on your spark plugs isn’t a normal condition, and it can be indictive a much more serious problem.

The oil on the spark plugs isn’t the problem – it’s how the oil got there that can damage your engine.

Can you Clean and Reuse Spark Plugs?

Absolutely! Once you’ve completed the necessary repairs to keep the oil from coming back, use a carb cleaner to spray down the electrode and threads and let everything dry. Once it’s dry, reinstall the spark plugs, and you’re good to go!

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Adam Mann

With degrees in both Automotive Technology and Journalism and Mass Communication, Adam brings a unique blend of expertise and passion to every article he writes.

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