Oil On Spark Plug Threads Or Wells? Here’s Why And How To Fix

Fixing the problem of oil on spark plug threads or wells may be as simple as cleaning the plugs and/or replacing a valve cover gasket. But if the problem is not fixed in time, it can lead to engine failure.

Spark plugs are found in the engine’s combustion chamber and provide the energy needed to create combustion to get the engine running. There is generally one spark plug per cylinder.

Spark plugs interact internally with the engine’s oil. But if you see oil on a spark plug’s threads or wells, that’s a problem because it’s not supposed to be there.

It suggests that there is an oil leak somewhere coming from an external origin.

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Signs Of Oil Leaking Onto The Spark Plugs

two spark plugs

Spotting an oil leak in your vehicle is never a good thing. And if you have a problem with oil leaking on the spark plug threads or wells in your car or truck, it can quickly become a more concerning issue.

One sign that there may be oil on the spark plug threads or wells is that the vehicle’s performance starts to suffer. The engine becomes sluggish and less powerful.

The problem will result in an uptick in oil consumption as well.

One car owner who commented in an online auto forum said that his affected spark plugs “definitely looked like there were 100K miles on them when, in fact, it was more like 30K.”

Spark plug threads or wells flooded with oil may cause a noticeable decrease in engine power before eventually leading to total engine failure.

The problem could cost you a small fortune if it’s not caught early and fixed.

Why Is There Oil On My Spark Plug Threads Or Wells?

auto spark plugs

If you notice oil on your vehicle’s spark plug threads and cavities, it’s a sign of an oil leak.

The leak is likely coming from within the engine compartment. It may be due to a faulty or worn part such as an o-ring, piston, or valve cover gasket.

These parts and other rubber and silicone seals should prevent oil seepage. But time, use, and heat from the engine can wear down the seals and cause oil to leak on the threads and wells of the spark plugs.

This article covers oil-soaked spark plug problems in more detail, including causes, symptoms, and fixes.

How To Tell If You Have Oil On Your Spark Plug Threads Or Wells

If your vehicle has oil on its spark plug threads or wells, you’ll recognize it. There are a few typical signs to look for, including:

  • Engine performance is adversely affected, resulting in reduced performance and possibly misfiring or backfiring, which can lead to engine failure.
  • The smell of burning oil in the cabin may indicate oil-soaked spark plugs.
  • The exhaust begins to emit blueish-gray smoke from the tailpipe.

How Serious Of A Problem Is Oil On Your Spark Plug Threads Or Wells?

car check engine light on

On a scale of one to 10, having oil on the spark plug threads or wells is a three that can quickly become a 10.

Having oil on your spark plug threads or wells can cause your car’s “Check Engine” light to engage and can lead to engine problems like a blown head gasket and misfirings.

More seriously, it can also ruin your catalytic converter and even cause total engine failure.

Luckily, if you detect the issue at an early stage, you can substitute or wash oil-drenched spark plugs and continue using them.

How To Fix It: Cleaning Oil From Spark Plugs May Fix Related Engine Problems

Poor Performance

Faulty spark plugs with oil on the threads or wells will adversely affect the engine, which has to rely on fewer cylinders. The vehicle’s performance may become sluggish, and the engine may misfire.

Failed spark plugs may also cause battery drain.

These issues are why it is vital that you catch and fix the problem early by replacing or cleaning the affected spark plugs.

Often, the problem is fixed simply by replacing a cracked or leaking valve cover gasket or the o-rings.

Can Spark Plugs With Oil On Their Threads Or Wells Be Cleaned And Used Again?

Fortunately, replacing spark plugs is relatively affordable.

Your average copper spark plugs cost around $5 to $10 each. Premium plugs can go up to $50, and iridium performance spark plugs can reach $100.

One more option to solve the issue is to remove the oil from the spark plug threads or wells. YouTube offers numerous instructional videos explaining different cleaning techniques.

One option is to use a wire brush to scrub the oil from the spark plugs and sandpaper to remove oil debris from the electrodes.

Additional ways to eradicate oil from spark plug threads include using canned carburetor cleaner, an air gun, or even a blowtorch for tough jobs.

Or you can spend $20 to $30 for a pneumatic spark plug cleaner that uses air to clean the plugs.

How Long Does It Take To Replace Spark Plugs?

60 Minutes Wait Time

Replacing or reinstalling spark plugs is a relatively simple procedure that should take about an hour.

The cost of a professional installation ranges from $100 to $350.

How To Fix Oil-Soaked Spark Plug Threads Or Wells

Spark plug threads or wells fouled with gunk are not necessarily unusable. You can clean oil-drenched spark plug threads.

Use simple household products like paper towels and Q-Tips to remove the initial layer of oil.

Of course, tougher oil-soaked grime requires mightier methods to clean the spark plug threads or wells. Many YouTube videos are available featuring DIYers and shade tree mechanics showcasing a variety of effective cleaning methods, from relying on air pressure to using a blowtorch.

Effective Methods For Removing Oil From Spark Plug Threads And Wells:

  • Soak up the initial layer of oil in the threads and wells with absorbent paper towels and Q-Tips.
  • Spray brake parts or carburetor cleaner on the oily threads or wells to dissolve and remove the oil with a towel.
  • Use a can of compressed air and a microfiber cloth to remove stubborn oil residue.
  • Scrape off the oil with a steel wire brush and sandpaper.
  • Take a blowtorch to spark plug threads and wells with caked-on oil. 


Discovering oil on the threads or wells of your spark plugs can escalate into a significantly more crucial concern if left unaddressed promptly.

Luckily, the solution is affordable and involves cleaning or replacing your spark plugs.

But if the problem is not found and fixed early, it can result in engine damage and costly repair bills.

So, take notice if you smell burning oil in your vehicle’s cabin or see bluish-gray smoke emitting from the tailpipe because there could be trouble with oil on your spark plug threads or wells.

Fixing the problem could be as simple as cleaning the oil from the spark plugs or replacing a valve cover gasket before the issue results in total engine failure.

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David M. Ciminelli

David M. Ciminelli is a Southern California-based journalist and longtime auto enthusiast who has contributed to a plethora of popular automotive sites.