How often do spark plugs need to be replaced in lawn mowers?

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Written By Janine Clarke

I am Janine Clarke AKA Equipment Girl, a nerdy girl with an unhealthy knowledge about power tools and gardening! You can contact me here.

Knowing how to replace spark plugs is one thing – and it’s relatively straightforward. But knowing when to do it, that’s a whole other issue.

You see, a lawn mower spark plug is quite a hardy piece of electrical equipment, considering it’s such a small part of an otherwise highly mechanical engine. But without it, the engine couldn’t start or run.

That means staying on top of your spark plug is essential if you want to make use of your lawn mowers this mowing season.

Whether it’s a push mower or a riding mower, spark plug issues can quickly put a stop to your manicured lawns. But just how often do lawn mower spark plugs need to be replaced?

Well, that’s exactly what I’m here to talk about today. I’ll cover everything from the signs that a bad spark plug needs replacing, to general small engine maintenance tips and tricks to keep your lawn mower in working order so its spark plug doesn’t need replacing as regularly.

Ready to find out more? Then join me below!

When Will My Lawn Mower Spark Plug Need Replacing?

With a standard lawn mower, you can expect to use it over multiple seasons without it needing to be replaced so long as you keep on top of the maintenance side of things (more on this later).

For many people, though, it’s just easier to pick up a replacement spark plug at the start of each season to make sure the lawn mower performs as it should until next year. Would I recommend you do that? Not really.

For me, that seems a waste of money, and if your lawn mower is in good shape and working properly by the end of the season, it seems strange to replace the spark plug unnecessarily early.

However, sometimes you won’t have a choice.

When Problems With Lawn Mower Spark Plugs Arise…

Your spark plug ignites the air fuel mixture in the combustion chamber to make the engine start and run. Without that initial ignition spark, your lawnmower wouldn’t be able to run at all.

If you notice any of the following symptoms, then it might be a sign that you need to change the spark plug in your lawn mower:

The above four scenarios may mean it’s time to replace the spark plug, but if everything is running fine, you shouldn’t need to replace your lawnmower’s spark plug often at all.

Why Does My Lawn Mower Spark Plug Need Replacing?

I’ve covered the when, but what about the why?

If you’ve noticed the issues I mentioned above, then there are a number of causes that might be the reason why you have bad spark plugs. It could be just one of the explanations below, or a combination of other factors too. It’s difficult to say.

Either way, any or all of these could explain why your spark plug is no longer working as it should and you need to replace it:

It’s Worn

After hours of use, it’s quite common for spark plugs to become overly worn. Spark plugs wear down naturally the more you use them, and as this happens, the mowers spark plug might not be able to create an adequate spark to ignite the fuel and air mixture that the carburetor has delivered to the cylinder.

If it’s worn, then the spark created (if it’s able to create a spark between the two electrodes at all) might not be strong enough to ignite the fuel. The gasoline in your engine needs the ignition to set things in motion, because it’s the gas and air burning that moves the mechanical parts of the engine and rotates the mowers blade.

If, after hours of use, you’ve noticed that the engine is stuttering more, has less power, or won’t start at all, then the chances are the spark plug is worn and you’ll just need to replace it with a new spark plug.

You can usually tell if a spark plug is worn on this type of outdoor power equipment by looking at the porcelain sheath that covers it. If it’s cracked or damaged, then the spark plug is worn and needs replacing.

It’s Fouled

A fouled spark plug is a little different to a worn one. Oil fouling is when the engine is burning oil in the cylinder, which then misshapes the spark plug until its no longer usable. You might also notice excessive fuel in the cylinder as another symptom of this type of fouling.

When this happens, there isn’t anything you can do to fix it. You’ll simply need to invest in some new spark plugs because the old one will be too misshapen to do the job of igniting the gas effectively.

Typically, if your gas runs out quicker than it used to when doing your normal lawn care routine, then it’s likely that your spark plug is fouled.

Spark plugs last a long time after they’ve been installed in the engine block, so if you notice problems with your lawn mower soon after you’ve replaced the spark plug (or you’ve bought a brand new lawnmower) then the chances are it’s an oil fouling issue.

It’s Not Been Maintained Properly

This is probably the number one reason why you need to change your spark plug so often. Like I said, they don’t need replacing often once they’ve been installed, but only if you do the proper spark plug maintenance.

If you just leave them alone, then it’s easy for carbon buildup and debris to affect the way the spark plug functions, making you think you need to replace your spark plugs, when actually, they just need a little TLC perhaps with some WD40 or alternatives.

How To Maintain Your Lawn Mower Spark Plugs So They Need Replacing Less

Below, I’ll quickly cover everything you need to get your spark plugs in order. I’d recommend doing these basic maintenance checks every 1/4 of the mowing season or so, because it’s a simple fix that will mean your spark plugs last much longer.

What You’ll Need

Spark Plug Socket Set

Spray On Spark Plug Cleaner

Soft Wire Brush

How To Clean Spark Plugs

Clean spark plugs are effective spark plugs. Start by removing the spark plug from the engine block using your spark plug socket. These devices are designed to remove spark plugs quickly and easily. Once it’s loose, just remove the spark plug lead so you can clean the spark plugs effectively.

Spray on the cleaner, and use a soft wire brush to remove any excessive carbon or debris from the spark plug. Be gentle. You don’t want to bend the electrodes out of shape or alter the spark plug gap. I actually covered recently about gaps in spark plugs “are lawn mower spark plugs pre-gapped?“.

Whilst you’re here, check the air filter too. If this is full of carbon, then that will explain why your spark plugs are covered in it too. Clean this out to prevent further buildup.

Once it’s clean, simply reinstall your spark plugs and you’ll be ready to continue with your lawn care routine as planned!

Everyone just uses simple DIY foam for an air filter

Final Thoughts

You shouldn’t need to replace spark plugs often. Some people choose to do so at the start of each season to prevent any unexpected surprises, but if you look after your spark plugs by cleaning and maintaining them regularly, then there’s no reason why you’d need to do this.

As with most things in the outdoor power equipment world, the proper care and attention will go a long way!