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Car Care Advice

8 Reasons for Oil on Spark Plugs (Including Symptoms & FAQs)

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Oil is a vital lubricant in a well-functioning engine, but your spark plugs are not the place it should be. 

Oil on spark plugs can indicate much larger engine problems. So you’ll want to watch for common signs indicating excess oil on your spark plugs.

But how do you fix oil on spark plugs?
And can you drive with oily spark plugs?

We’ll tackle these questions and go through the usual symptoms and common causes of oil on spark plugs, as well as answer some FAQs.

This Article Contains

Let’s begin! 

6 Symptoms of Oil on Spark Plugs

Here are six signs there’s engine oil on your spark plugs:

1. Blue Smoke from Tailpipe

If you have engine oil on your spark plugs, these electrodes won’t create a reliable spark. So, your engine compensates by increasing the air to fuel ratio in your cylinders.

Any unburnt fuel exits via the exhaust valve and appears as blue smoke from your tailpipe.

2. Gas Smell from Exhaust

When there is an oil leak on your spark plugs, the engine will have a slightly richer air/fuel mix on startup. 

Cold fuel is more difficult to vaporize, so more fuel is needed to create a combustible fuel air mixture. When there is oil on the spark plugs, this cold fuel problem is compounded, which causes more fuel to be dumped directly into the exhaust.

This produces a strong gas smell from the exhaust pipe.

3. Increased Fuel Consumption

Without a reliable spark from your spark plugs, your engine has to account for the underperformance. It does so by increasing fuel in your cylinders to maintain the pressure in your combustion chamber.

As a result, your fuel economy worsens, and oil consumption increases.

4. Decreased Engine Performance

If the fuelair mixture in your cylinders isn’t igniting reliably due to a bad spark plug, there won’t be enough pressure to push your pistons down with the required force. 

This results in an acceleration lag and decreased engine performance.

5. Engine Misfire

An engine misfire is caused by incomplete combustion inside one of the engine cylinders, sometimes due to an oily spark plug. 

This could lead to engine problems and result in shakes while driving or idling.

6. Engine Backfires

When the fuel-air mixture in your cylinders doesn’t burn properly because of oil contamination and excess oil deposits on your spark plug threads, fuel may shoot out your exhaust pipe and sound like a mini-explosion as it combusts externally. 

This happens when your spark plug can’t burn off all the fuel before your exhaust valve opens. 

Next, let’s look at some common reasons for oil on spark plugs.

8 Causes of Oil on Spark Plugs

There are several causes for oil leakage on these tiny electrodes. 
Here are the eight most common reasons:

1. Leaky O-Ring Seal

Leaky O-rings (spark plug tube seals) are probably the number one cause of oil on spark plugs. Spark plug tube seals keep engine oil, coolant, and everything else on one side of your spark plugs, so they remain dry. 

If these rings fail, engine oil can leak into your spark plug well and onto your spark plugs.

2. Faulty Piston Compression Rings

The piston compression rings seal the small space between the piston and the cylinder wall. 

They collect excess engine oil from the cylinder walls and transfer it to the oil pan to prevent oil leakage in the combustion chamber.

Worn-out piston rings can be caused by normal wear and tear, leading to an oil leak in your combustion chamber and spark plug hole. 

3. Worn Out Intake Valve Seals

Intake valves regulate air and fuel inflow while controlling exhaust outflow. If their valve seals wear out, motor oil can enter the crankcase combustion chamber and cause oil fouling in your spark plug well.

4. Blown Head Gasket

The head gasket sits between the piston head and the engine block, sealing off the combustion chamber and preventing oil contamination and depositis on your spark plugs. It also prevents coolant and motor oil from mixing together as they travel to the cylinder head via the oil lubrication system. 

Motor oil can get into the combustion chamber if you have a blown head gasket and leak into your plug wells and onto your spark plug threads.

5. Leaking Valve Cover Gasket

The valve cover gasket sits on top of your cylinder head and is exposed to high temperatures. It keeps oil on one side of your cylinder head and away from the rest of the engine. 

If you have a leaking valve cover gasket, your spark plug threads and the corresponding ignition coil or spark plug wire can be subjected to oil fouling.

6. Worn Valve Guide

Your valve guide sits on your cylinder head and controls how your combustion chamber receives air. It has a dedicated valve stem seal, and a faulty seal or valve guide can lead to spark plug fouling.

7. Clogged Crankcase Ventilation

Indicated by oil deposits on your spark plug tips, a faulty or clogged crankcase ventilation valve (PCV valve) results in oil forcing its way into the combustion chamber from your oil pan — causing spark plug fouling.

8. Broken Piston or Worn Cylinder Wall

Pistons are subjected to high temperatures and movement when functioning regularly in an engine. Therefore, normal wear and tear can sometimes lead to faulty pistons or cracked cylinder walls — causing an oil leak in the combustion chamber and spark plug well.

With that in mind, let’s examine three FAQs and their answers about oil on spark plugs.

3 FAQs About Oil on Spark Plugs

Here are three commonly asked questions about oil on spark plugs:

1. How Do I Fix Oil on Spark Plugs?

Firstly, before fixing an oily spark plug or buying a new plug, you need to troubleshoot and address the root cause. Otherwise, the motor oil will just keep returning, leaving you with a fouled spark plug and an increased risk of engine damage.

Secondly, it’s always best to let an automotive professional handle any repairs rather than handle them yourself.

But, if you do choose to fix an oily spark plug yourself, here are the steps you can follow:

  1. Turn off your car’s engine, pop your hood, and disconnect your battery.
  2. Remove your valve cover using a screwdriver (this may be tough as silicone is often used to seal the valve cover).
  3. Detach each spark plug wire (or coil pack) and use a spark plug socket to remove each bad spark plug and spark plug boot.
  4. Remove your old gasket and/or O-ring seals from your cylinder.
  5. Clear off any traces of your old gasket on your valve cover using plastic tools (not a metal screwdriver).
  6. Using a degreaser, clean your cylinder head and valve cover.
  7. Clean each spark plug thread and tip with carb cleaner spray.
  8. Using a spark plug socket, install a new plug.
  9. Install a new gasket and O-rings.
  10. Reinstall your valve cover and reconnect your battery.

2. Can I Drive with Oil on My Spark Plugs?

In short, yes. 
Think of spark plugs as the heartbeat of your car. Without them, the car won’t work at all. When they aren’t healthy, the car won’t perform to its maximum potential. 

Oil on a spark plug or in your spark plug hole isn’t the real issue. It’s how the oil got there that really matters. 

If it were just an oily spark plug thread or tip, your car’s engine would burn away the oil, and that would be the end of it.

However, having oil on your spark plug threads or in your plug wells for a prolonged period is a serious problem that can result in a misfire, increased oil consumption, and increased fuel consumption. 

It can even lead to engine damage and destroy components like your catalytic converter.

So, ignoring an oily spark plug and its root cause isn’t something you want to do unless you want an expensive replacement job in the future.

3. How Can I Prevent Oil From Leaking onto the Spark Plugs?

There are a few preventative measures you can take to stop oil from leaking onto your spark plugs:

Final Thoughts

Your spark plug threads and plug wells are not places where oil should be. There are multiple signs to look out for, like an illuminated check engine light or blue smoke from your exhaust pipe.

There are also several reasons for oil on spark plugs, like a blown head gasket or worn compression rings. If you ignore any of these issues, you risk serious problems like a broken catalytic converter.

So what’s the best thing to do?
Reach out to AutoNation Mobile Service

AutoNation Mobile Service is an automotive repair and maintenance solution with competitive, upfront pricing for all your vehicle repair needs, from an oil change to a head gasket and piston ring replacement. And the best part is, we come to you!

Contact us today to get a cost estimate, and our expert technicians will be over to perform a compression test and find the root cause of your oily spark plugs in no time.