3 Possible Reasons for Oil in Spark Plug Well + How to Clean It?

Sweating bullets over oil in your spark plug well?
Don’t panic yet!

Oil in the spark plug well typically results from a leaking valve cover gasket or worn seals — issues that a mechanic can easily resolve. However, if the oil enters the combustion chamber, it becomes a serious concern that could lead to costly repairs.

Keep reading to discover three likely reasons for oil in your spark plug well. We’ll also explain how to clean it and why ignoring this problem is a bad idea.

This Article Contains:

3 Alarming Causes of Oil in Spark Plug Well
5 Serious Causes of Oil on Spark Plugs
How to Remove Oil From Spark Plug Wells
3 FAQs about Oil in Spark Plug Well

3 Alarming Causes of Oil in Spark Plug Well

Oil often seeps into spark plug wells due to external engine problems such as leaking valve gasket cover, worn O-rings, or overfilled engine oil.

Let’s dive into the specifics of how this happens:

1. Leaking Valve Cover Gasket

A valve cover gasket sits between the valve cover and the top of the engine cylinder head. It keeps the engine sealed and prevents oil from leaking out.

Over time, the engine heat causes the valve gasket cover to crack and become hard or brittle. If the gasket fails near the spark plugs, oil can flow into the spark plug hole, contaminating the spark plug threads and wires.

2. Worn Spark Plug Tube Seal or Leaky O-Rings

Many engines have valve covers with openings for the spark plugs and ignition coils. A spark plug seal prevents oil from leaking into these openings. Some engines also have O-rings in the cylinder head for extra protection.

When the spark plug tube seal or O-rings fail, oil can enter the wells and damage the spark plug wires and plug body, causing premature failure.

3. Engine Oil Leak

Excess oil in the engine creates extra pressure in the crankcase. This additional pressure can strain gaskets and seals around the valve cover and spark plug tube.

If these seals fail, the oil will leak into the spark plug hole, resulting in engine misfires.

While external problems cause oil to pool in the spark plug wells, internal leaks result in oil appearing directly on the spark plug. This indicates a severe problem that needs immediate attention, so let’s explore its causes.

5 Serious Causes of Oil on Spark Plugs

If you notice oil on the tip or threads of the spark plug inside the combustion chamber, it’s likely due to an internal engine issue.

Here are some common causes:

Faulty piston ring: A worn or stuck piston ring allows oil to enter the combustion chamber, coating the spark plug threads with oil. Moreover, if the cylinder wall is worn, the rings won’t seal the cylinder properly, allowing oil to enter the combustion chamber.

Worn-out valve guides and seals: Your engine uses valve guides to ensure proper valve movement and valve seals to prevent oil from leaking into the combustion chamber. If valve seals wear out, oil can leak and damage the spark plugs, causing the engine to burn more oil.

Blown head gasket: The head gasket seals the combustion chamber, preventing coolant and oil from mixing. However, a blown head gasket causes oil to leak into the combustion chamber and contaminate the spark plugs. In such cases, replacing the spark plug won’t work; you’ll need a new gasket.

Positive crankcase ventilation (PCV) system problems: Modern cars have a PCV valve that reduces emissions by redirecting engine vapors into the combustion chamber. If the PCV valve malfunctions, oil gets drawn into the air intake, fouling the spark plugs.

Cylinder deactivation and variable valve timing issues: The Variable Valve Timing (VVT) and deactivation systems help improve fuel efficiency and engine performance. However, these systems can create high vacuum levels that pull oil past the piston rings, leading to oil-fouled spark plugs.

Next, let’s see how to get rid of the oil in your spark plug well.

How to Remove Oil From Spark Plug Wells

Before cleaning the oil, ensure the vehicle is off and the engine is cool. Once that’s done, here’s how you can remove oil from spark plug wells:

Note: These steps can temporarily remove the excess oil, but it can return if the underlying problems aren’t fixed. If you’re not confident with car parts, let a mechanic do it.

Wrap a paper towel around a pen with the same diameter as the spark plug and lower it into the spark plug well to soak up the oil.

Soak up as much oil as possible, spray brake cleaner into the spark plug well, and blow it out with compressed air.

Check and adjust the torque of the valve cover bolts to the manufacturer’s specifications to prevent oil leakage into the spark plug wells.

If oil appears in the spark plug wells despite tightening the valve cover bolts, get your vehicle examined. Depending on the issue, the mechanic will install a new gasket or O-rings.

Note: Fixing an oil leak inside the combustion chamber is more complex, so it’s best to have the repairs done by professionals.

Have more questions?
Keep scrolling.

3 FAQs about Oil in Spark Plug Well

Here are answers to common queries about oil in spark plug wells:

1. What Happens if There’s Oil in the Spark Plug Well?

Oil in your plug wells leads to:

Fouled spark plugs: Oil-filled spark plug wells contaminate the electrode and spark plug threads, leading to rough idling and reduced engine performance. To fix this, you’ll need to install a new plug.

Engine misfires: Oil-soaked spark plugs struggle to create a spark, causing ignition issues, misfires, and an illuminated Check Engine Light.

Low oil levels: Oil leaks into the spark plug wells can reduce oil levels, depending on the severity of the leak.

Soaked ignition coils: Oil in the plug wells can soak the ignition coil, coil pack, spark plug wire, and spark plug boot, leading to deterioration and potential failure.

2. Is It Safe to Drive with Oil in Spark Plug Wells?

No, driving with oil in the spark plug wells isn’t safe. It can reduce engine performance and damage the ignition system components. Over time, unresolved oil leaks can cause severe engine damage and significantly increase repair costs.

3. How Much Does It Cost to Resolve Oily Spark Plug Well Issues?

Fixing problems that cause oil to pool in your spark plug well varies depending on the parts that need replacement, your vehicle’s model, and local labor rates.

That said, here’s the estimated cost (including labor) for different components:

New valve cover gasket: $110 to $340
Spark plug seal tube: $190 to $390

Keep Your Spark Plugs Oil-Free with AutoNation Mobile Service

Oil in the spark plug wells causes misfires and compromises your vehicle’s safety. That’s why it’s crucial to identify and fix the underlying issues promptly.

Need help diagnosing the problem?
AutoNation Mobile Service’s mobile mechanics can come to you, identify the cause, and replace the faulty parts. We’re a mobile auto repair and maintenance solution offering easy online booking and a 12-month | 12,000-mile repair warranty.