How Long Does a Lawn Mower Spark Plug Last?

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So, how long does a lawn mower spark plug last?

Typically, a lawn mower spark plug can last up to 25 hours of use, before needing a replacement. 

Some parts of your lawn mower can last the entire lifespan of the mower, but the spark plug is unfortunately not one of them. 

Spark plugs are meant to be replaced after certain hours of use. That means the spark plug of a lawn mower used for residential mowing might last longer than one used for industrial mowing. Learn more about the best spark plug for lawn mowers.

A bad spark plug will affect the efficiency of the lawn mower in different ways. However, not every bad plug needs to be replaced. Sometimes, you just need to clean and reinstall it, and it will keep firing your engine again. 

What Makes a Spark Plug Go Bad?


Unfortunately, lawn mower spark plugs are not made to last long. It doesn’t matter how well you try to maintain them, all spark plugs will eventually wear out. That’s their nature, and there is little you can do about it.

After a period of use, the electrodes on the plugs will wear out, making them so reduced that they are no longer sharp or long enough to create the necessary spark needed to run the engine.

However, if your spark plug is malfunctioning even though it’s not worn out, there may be other factors responsible for this, such as:

Carbon buildup around the plug 

This usually happens when there is too much debris getting into the plug chamber due to a clogged air filter, cracked distributor case, or dirty fuel injector.

Damage to the electrodes

When the electrodes at the bottom of the plug are cracked, chipped, or worn too much, then the spark plug may not function properly.


This can gradually widen the space between the electrodes and the center of the plug, making the spark plug less effective.

Oil contamination 

When oil continually seeps into the spark plug, it will damage the tip, causing oil to leak into the combustion chamber.

Using old gasoline

leaving gasoline in the tank over the winter without adding a stabilizer will cause it to deteriorate. When you run such gasoline in the engine, it creates a kind of residue that accumulates on the spark plug insulator and shorts it out.

Water in the gasoline 

Water can wet the plug and short-out the spark. But simply removing the plug and drying it can fix this.

Mixing too much oil

This is especially true for a mower with a 2-cycle engine. Mixing too much oil into the gasoline can foul the spark plug with oil that was not completely burned.

How Can I Tell If the Spark Plug of My Lawn Mower is Bad?

It is not very difficult to tell when your spark plug is bad. Different signs give that away. Below are some of them:

Difficulty getting the engine to fire up

This is usually the first sign that your spark plug needs attention. 

A bad plug can make it pretty hard to get your engine to fire up — the engine of the lawn mower will keep turning over but won’t start. It shows that the plug is not producing enough spark or not sparking as quickly because it’s dirty or overly worn.

Lawn mower keep dying

Also, if after your lawn mower has started working, it keeps dying while mowing, it could be a sign that your spark plug is bad. When spark plugs are bad, it is normal for them to become unreliable and inconsistent in their functioning.

Gas running out quicker than normal

Do you have to refill your tank more often than you used to? It could be a sign that your spark plug is bad. 

Faulty plugs oftentimes won’t be burning all the fuel because it’s weak. Therefore, lots of fuel will be moving through the chamber without being burned, causing your tank to run out quicker than expected. 

Do I Need a New Spark Plug for My Lawn Mower?

It depends. You don’t necessarily have to replace your spark plug everytime it is under-performing. Sometimes, you just need to remove it, clean it, reinstall it, and it will be back firing. 

But if you see that the top of your spark plug is rounded, then getting a replacement is recommended.

On the other hand, if the spark plug is in good shape but just dirty, wet with gasoline, or clogged with carbon, you don’t need a replacement. All you need is to get a wire brush and clean it thoroughly. Then adjust the gap between the electrodes and restore it.

How Do I Clean and Reinstall a Lawn Mower Spark Plug

How Do I Clean and Reinstall a Lawn Mower Spark Plug?

If your spark plug is still in good shape, then you can consider cleaning and reinstalling it. It is very easy, and in a few minutes, you will be done with the whole thing.

Step 1: Get necessary tools for the job

You will be needing a couple of tools, including a spark plug socket to remove the plug. You will also need a spark plug spray cleaner or a soft-wire brush for the cleaning.

Step 2: Carefully remove the plug

Use the spark plug socket to gently remove the plug by applying a reasonable amount of force. 

But if it still won’t turn even after some force, spray a little WD-40 or some other type of lubricant. Give it a few minutes to soak into the tight spaces around the plug. Then try again to loosen it. 

Step 3: Clean the spark plug

When the spark plug is out, use the soft-wire brush to gently remove anything that might have accumulated on it. You can also use the spark plug spray cleaner for this. But make sure you are cleaning in such a way that you are not causing any damage that can render the plug unusable. You surely don’t want to incur any extra cost from a damaged plug.

Step 4: Reinstall the plug

Once you have cleaned the spark plug, you can go ahead to reinstall it in the mower. Use the spark plug socket to tighten it back into its place.

What Kind of Spark Plug Goes In a Lawn Mower?

Lawn mower gasoline engines and automobile gasoline engines don’t use the same type of spark plugs. There is a structural difference in the plugs. So when getting a spark plug for your lawn mower, ensure you are getting the right type.

You will need to choose a “small engine” spark plug with a thread size between 10mm and 12mm. spark plugs for car engines usually have a larger thread. Your spark plug should also be around 3/8-inch long.

However, when installing your plug, ensure you set the proper gap that matches your engine’s requirement. A smart way to get this is to check your lawn mower manual.

What Happens If I Use the Wrong Type of Spark Plug for My Lawn Mower?

It is always good you choose the right plug type for your mower. When the spark plug is too long, it can cause terrible damage to your lawn mower’s engine.

On the other hand, if the plug is too short, you will regularly experience poor performance and a need to refill your tank more than usual.

One way to always tell if you have installed the wrong type of spark plug is if the electrodes are broken off or flattened.

Can I Clean My Spark Plug with WD-40?

Yes, you can use WD-40 to clean your spark plugs. It doesn’t have any damaging effects on it. Rather, it will make it easier to remove and clean the plugs. Plus, WD-40 can help form a coating around your plug that will help repel water and prevent corrosion.

How Can I Maintain My Lawn Mower Spark Plug?

Although lawn mower sparks plugs have a limited lifespan, properly maintaining them will help reduce conditions that prematurely shorten their lifespan. Both seasonal and in-seasonal maintenance is important here. Here are some tips to help you maintain your spark plugs:

#1: Clean or replace a clogged air filter


It is normal for air filters to clog over time. Remember that their primary function is to catch any dust and airborne debris before they make their way to the carburetor. 

But as debris begins to build up, it prevents enough air from getting to the engine’s combustion chamber for efficient use of fuel.

Excess debris and fuel can, however, damage the spark plug, and can also cause it to corrode. So, make it a point of duty to regularly clean the air filter. 

Use a clean piece of paper towel when cleaning so you won’t cause any damage to the filter.

#2: Stabilize the fuel during winter

Stabilizing fuel during the winter prevents the fuel from degrading, and also prevents water from settling out of it. Both degraded fuel and water are not good for your spark plug.

#3: Clean the deck


Don’t allow grass or other debris to remain on your mower. These can attract mice and other rodents during the cold months. These animals have a knack for chewing, and your spark plug wires may not be spared, too!


Lawn mower spark plugs are not built to last long but they can last up to 25 hours of use. Chances are that you would not go beyond this if you are using your mower only for residential purposes. 

You can always clean the plug and get it back into shape. But if you are in doubt, you can just go ahead to replace it. 

Spark plugs are relatively inexpensive, so if you are not sure if the old one is still in good condition or not, just replace it and move on.