How to Clean Spark Plugs the Right Way: Our Guide How to Clean Spark Plugs the Right Way: Our Guide

Whether it’s a car, a boat or a lawnmower, everything with an engine has one small part that plays a big role in keeping it humming. That is the spark plug. Spark plugs are vital pieces to any engine, so knowing how to clean spark plugs is an important thing for owners of those engines to keep in mind. Staying on top of spark plug maintenance will go a long way to making sure those engines keep on running.

What Are Spark Plugs?

Photo of a spark plug

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An engine has a series of cylinder-like chambers, each of which contain a disk or moving cylinder called a piston. For an engine to work properly, the piston has to move up and down. The piston moves by using the force of a small explosion caused by the spark plug.

Piston Action

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When a piston moves down, it draws fuel into the chamber. When the piston moves up, it compresses the gas in the chamber. That’s when the spark plug sparks, and that spark comes into contact with the compressed gas. The resulting explosion forces the piston back down, and the force from each chamber’s explosion then transfers to a crankshaft. From there, the energy allows vehicles to move and lawnmowers to cut grass.

Plug Specifics

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How many spark plugs are in an engine depends on the size of the engine. Small engines typically have one spark plug, while a four-cylinder engine has four plugs. A six-cylinder engine has six spark plugs and so on.

Spark plugs range in size from 10 millimeters to about 20 millimeters. According to the website,, spark plugs are classified as “hot” or “cold.” All that means is that hot spark plugs keep heat longer between explosions than the cold ones thanks to a longer core nose on the inside. Some have a sealing washer at the top of the thread while others have a tapered seat. Some spark plugs fit into different kinds of holes and must be tightened differently.

Each spark plug has electrodes that must be kept clean to produce a proper spark. The gap between electrodes and arms should be maintained at whatever distance the manufacturer says. And people should always use the spark plug recommended for their machine unless it is an unusual and temporary situation.

The Problem With Dirty Plugs

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Dirty, worn out or damaged spark plugs won’t be able to create a powerful enough spark. This may lead to excessive fuel consumption, slow acceleration or other issues with the engine. In fact, a troubled spark plug may be the reason an engine won’t start. Knowing how to clean spark plugs may resolve some of these problems.

Spark plugs are typically inexpensive to replace but are also easy to repair and maintain if you know how to clean spark plugs.

How to Check Spark Plugs

Photo of an engine with a spark plug

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An engine has a series of cylinder-like chambers, each of which contain a disk or moving cylinder called a piston. For an engine to work properly, the piston has to move up and down. The piston moves by using the force of a small explosion caused by the spark plug.

Take a Look

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Maybe the engine won’t start or it’s been a while since someone checked the spark plugs. Either way, taking a periodic look at them is a good idea. Doing so may rule out certain causes of engine problems or help prevent future issues.

For small engines, such as lawnmowers, spark plugs should be checked once a season or after about 25 hours of use, says In vehicles, owners should try to look at their spark plugs after 20,000 miles. Some experts say, however, that drivers should check and clean plugs after 5,000 miles and replace them after 10,000. Obviously, that will depend on how a vehicle is driven; driving often at highway speed will wear down the spark plug faster. The gap between electrodes will increase about 0.001 inch for every 2,500 miles, which hurts the machine’s fuel efficiency.

The Process

First, label the lead wires of the spark plugs with masking tape to the corresponding chamber. That will help avoid mixing up the spark plugs. For vehicles, disconnect the negative terminal on the battery.

Next, remove the lead wires by the cap, not by the lead itself. Damage to the lead could cause the engine to misfire. Gently clean the area around the spark plug with a brush and do not brush any debris into the engine. Use a spark plug spanner or socket to unscrew the spark plug. Keep the spanner or socket straight and make sure it fits. A deep spark plug socket with a rubber liner and a universal joint prevents accidental damage to the plug, says

For cars with spark plugs that are hard to reach, the plug spanner with a universal joint head can help, but be careful not to let it tilt sideways and break the ceramic top of the plug. The spanner or socket must fit on straight and as far as it will go.

Take a long and detailed look at the spark plug. If there is a light, tan coating, then the spark plug is fine. If the spark plug has an oily, dark powdery or damaged appearance, or if the electrode has been burned away, then the plug needs to be cleaned or replaced. And if you replace one spark plug, replace the entire set of plugs in the engine. Depending how much the spark plug is covered by oil or debris, it may be a good idea to have the engine checked when the plugs are replaced.

Fortunately, if you know how to clean spark plugs, cleaning all of them won’t be a difficult task.

How to Clean Spark Plugs

What Is Causing the Problem?

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There are a few ways that a spark plug can get dirty or damaged. A damaged valve seal or piston ring may allow oil to leak into the piston chamber. If the engine hasn’t run for a while or idles for too long, that may affect how a spark plug works. An air-to-gas ratio that is off can also cause problems.

Fuel, oil or debris buildup over time may affect a spark plug’s performance. Many people just replace spark plugs, but if a person knows how to clean spark plugs, they’ll likely save themselves a few bucks.

Tips for Cleaning Spark Plugs

Tip #1

In most cases, a dirty spark plug can be cleaned with sandpaper, usually 120 grit or higher but no more than 220 grit. If the electrode gap is large enough, fold the sandpaper in half and slide it between the electrode and the arm. Rub the sandpaper back and forth to get the grime off. Clean spark plugs one at a time.

Tip #2

If the sandpaper doesn’t fit in that gap, don’t fold the sandpaper in half. Instead, keep it flat and remember to sand all sides. Blow off the sanded areas with an air hose.

Tip #3

Do not use sandpaper on iridium spark plugs. Sanding down an iridium spark plug could damage the tip of the electrode.

Tip #4

There are spray-on cleaners for spark plugs in small engines, but make sure they are designed for that particular task.

Tip #5

The treads on the spark plug can be cleaned with a small brush. The whole spark plug can be wiped clean with a cloth to remove any loose dirt. Do not put spark plugs in water.

Tip #6

In an emergency, for a damp or very dirty spark plug, the tip of the plug can be gently heated with a blow lamp. This will clean the electrodes and the inside of the plug.

Tip #7

There are also devices that are specifically designed to clean spark plugs. You can find these online, at most big box stores, and at any auto supply shop.

Tip #8

If sandpaper doesn’t work, your spark plugs can be cleaned with grit blasting or sand blasting, which propels abrasive materials at a rough surface in order to smooth it out. Several auto shops offer this service, and a home grit blaster that runs off of a car battery is also available. The spark plug fits through a rubber seal in the home grit blaster. Just a few minutes will clean even the dirtiest spark plugs.


Setting the Gap

Remember, the electrodes need a proper gap to create a proper spark. People can refer to the owner’s manual or a vehicle handbook for the gap specifications. There should also be a label under the hood of the vehicle that specifies this information.

In an article on how to clean spark plugs, says it is safe to lever the gap open carefully with a screwdriver, although a gapping tool is best. Do not use pliers and do not close the gap by tapping the outer electrode, as it will probably crack the insulator inside the spark plug.

A gapping tool is a gauge that measures the distance between the spark plug electrode and the arm. Most are inexpensive and provide a more accurate reading than an ordinary feeler.

Feelers may not be accurate because any slight unevenness inside the gap could distort the flexible blade, which would set the gap too wide. The gapping tool uses hooks to lever the electrode either way, a built-in file and a set of stiff gauges. The right gauge should go through the gap with a slight click.

The right tools make learning how to clean spark plugs that much easier.

Fit It In

Check that the threads and the holes on the spark plug are clean. Screw the spark plugs back in by hand at first, but be careful not to cross thread them. This can easily be done and can damage the cylinder head.

Making sure the spark plug is tightened properly is important, but be careful not to overdo the tightening. Tightening too hard can flatten the washer and make the plug ineffective or difficult to remove again.

Tighten each spark plug a quarter of a turn past the point of when it is hand tight. Reattach the labeled leads to their proper spots. If you detached the negative terminal from the vehicle battery, reconnect it.

After the Spark Plugs Are Clean

Illustration of a spark plug

Image via Pixabay

Once the plugs and battery are connected again, start the engine to make sure everything is fine and your spark plugs are working. If the engine tries to turn over for a moment and then fails, the spark plugs are working and the engine issue is something else. If the engine doesn’t turn over at all, there could be an issue with the ignition.

If you put away the lawn mower, the boat, the snow blower and other seasonal equipment, it is suggested you replace the spark plugs when you bring them back out for the season. There are also small engine tune-up kits available to help with maintenance at the beginning and end of each season.

Now that you know how to clean spark plugs, remember to check them periodically. Keeping them clean and their electrode gaps accurate will prolong the lifespan of spark plugs: and that will keep your engine running well too.

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