Informational Guide

How To Clean Spark Plugs

It’s essential to know how to clean spark plugs. We will walk you through the steps required in this detailed guide.

Automotive spark plugs are an essential part of the car's ignition system. To properly take care of them, it's essential to know how to clean spark plugs. We will show you why you need to know how to clean fouled spark plugs and walk you through the steps in this detailed guide.

Carbon fouled

A spark plug with dry black carbon deposits on the electrodes or insulator nose is carbon fouled. When this carbon accumulates, the insulation between the electrodes starts to deteriorate, causing a misfire. Carbon fouling is caused by a clogged air filter, rich fuel mixture, driving at low speeds for prolonged periods, having a spark plug heat rating that is too cold, or a faulty ignition system.

misfires plugs

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Oil fouled

If the spark plug is oil fouled, you will notice a black, wet oil deposit on the electrodes and insulator nose. This is another situation when engine misfires are prevalent. Oil fouling is caused by excessive oil making its way into the combustion chamber, either from having too much oil in the system or having worn-out valve guides or piston rings.

damaged spark plug

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Heavy ash deposits

Ash deposits that build-up on the end of the spark plug will also lead to a misfire. When these deposits reach certain temperatures, it can also lead to pre-ignition situations. Ash formation is caused by poor quality fuel, faulty engine condition, bad fuel additives, and burning oil.

rusty spark plug

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Overheated spark plugs end up with a white glazy or glossy insulator. You may also notice smaller black deposits, which indicate premature failure. Overheating is caused by a lean fuel mixture, a manifold air leak, insufficient octane rating of your fuel, poor lubrication or cooling, or from using a spark plug with too high of a heat rating.

carbon fouling plugs

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Signs of Faulty Spark Plugs

Reduced gas mileage

You might need to learn how to clean fouled up spark plugs if you notice a drop in fuel efficiency. Dirty spark plugs can impact your fuel mileage because they cause the engine to work harder than it should.

Lack of Acceleration

Another reason to learn how to clean NGK iridium spark plugs is when the vehicle stops performing normally. When the spark plug becomes contaminated or fouled, it can't spark correctly, causing a sluggish feel to your car.

Hard start

You may also want to figure out how to clean the spark plug hole if your vehicle isn't starting right. Once you rule out a dead battery or lack of fuel, it's time to inspect the spark plugs. When they foul, there's no way for the spark to form and begin combustion.

Engine misfires

Any time the engine starts to misfire, you want to figure out how to clean the spark plug well. Faulty plugs interrupt the combustion process, which leads the performance of your motor to suffer. Even if this happens for a minute, you can experience a misfire.

Rough idling

A final reason that you should consider learning how to clean iridium spark plugs is when the idle becomes rough. Fouled plugs make it difficult for the engine to run as it should and could also lead to vibration.

Steps on How to Properly Clean the Spark Plugs

There are multiple ways you can use when learning how to clean spark plug hole threads. Gather these supplies before getting started (not all are required).

Here are some general steps to follow.

  1. 1
    Take the spark plug out with your socket and ratchet wrench. If you take multiple wires out, make sure you label them so you remember where they go.
  2. 2
    Clean the spark plug with 180-grit or higher sandpaper. Sand it gently until all of the debris is removed. Then, use an air compressor to blow off the area you sanded.
  3. 3
    Or, you can clean the spark plug with some select liquids. First, wipe off the dirt with a clean rag. With a wire brush, remove any remaining deposits. Choose a cleaning liquid from mineral spirit, 90% alcohol or injector cleaner. Wear gloves when applying the liquid to the end of the spark plug. Dry it off and blow away any remaining dirt.
  4. 4
    You could also clean the spark plug with a sandblaster.
  5. 5
    Gap the spark plug with a gauge tool. Check your owner's manual to find the appropriate spark plug gap.
  6. 6
    Reinstall your spark plugs.

Tips & Techniques to Keep Your Spark Plugs Performing

Clean before removing the old spark plug

Before you remove the old spark plug, use compressed air to remove contaminants and debris from the area, so they don't end up in the cylinder. Otherwise, you will have to learn how to clean the spark plug hole once debris gets inside.

Always inspect a new plug for damage

Be careful not to drop your spark plug. If you do, it's important that you check it for damage. You also want to do this when installing new plugs to ensure there was no damage during transportation. Verify that the gap is also correct for ideal performance.

Spray the cavity around the center electrode

With a carburetor cleaner, you can spray out the cavity located around the center electrode to force debris out. You should do this with the plug faced downward.

Coat the thread with an anti-seize compound

If you apply an anti-seize compound to the threads of the cylinder head, you make it easier to remove the plugs. However, you want to keep it away from the electrodes. If it does get on the electrode, simply wipe it off with a rag containing carburetor cleaner.

Coat with dielectric compound

If you coat the secondary wire connection and insulator with a dielectric compound, you can prevent corrosion and keep the boot from sticking to the insulator.

People Also Ask (FAQs)

How do you clean a lawn mower's spark plug?

When you want to learn how to clean a lawn mower spark plug, simply follow the instructions for automotive plugs. Everything remains the same, other than you might have fewer plugs to clean.

Can I use WD40 for cleaning spark plugs?

Many people don't know that the WD stands for Water Displacement, proving that you can keep moisture away from spark plugs and remove carbon residue with this substance. Learn how to clean spark plugs with WD40 simply by applying a small amount and wiping it clean with a rag.

How long should spark plugs last?

It depends on what type you choose, but some will last up to 100,000 miles.

How often should you change NGK Iridium spark plugs?

NGK Iridium spark plugs will last anywhere from 40,000 to 80,000 miles, depending on the application. Check your owner's manual or reference NGK for more information.

How do you check and clean boat spark plugs?

Learning how to clean boat spark plugs is just as simple as working with automotive plugs. Use our simple tips above to keep your boat running it's best.

What happens if you don't gap your spark plugs?

If you don't gap the spark plugs accurately, the engine won't be able to perform correctly. Check the gap to optimize performance and improve efficiency.


Our steps can be used when you want to learn how to clean oil from a spark plug hole or how to clean a spark plug connector. By keeping your spark plugs in optimal condition, you ensure that the engine runs the way it should.