Why is My Lawn Mower Smoking?

You're out on a beautiful Saturday morning, ready to mow the lawn that's become overgrown and unruly over the course of just one week. You pull the cord, your mower comes to life, and then, out of nowhere: a puff of dark smoke. Then another. Soon, it seems like your machine is engulfed in its own personal weather system.

You begin to panic. Why is my lawn mower smoking? Is it going to explode? Do you need to call the fire department? Do you need to buy a new mower?

While smoke coming from your lawnmower is definitely a sign that something's not right, it's not always a catastrophic failure. More often than not, it's a problem you can diagnose (and even fix!) yourself.

Your first clue is often the color of the smoke, so let's decode what might be going on so you can stop playing lawnmower detective and get back to playing landscaper.

White or Blue Smoke

The most common culprit behind a smoking mower is an oil issue, and if the smoke is a white or bluish shade, then this is where your investigation should start. There are a few different scenarios that could be playing out here:

You Overfilled the Oil Reservoir

This is probably the single most frequent reason for a smoking mower, especially right after you've done some maintenance. You were being a responsible owner, checking the oil, and maybe you added just a little too much. It's an easy mistake to make.

When the oil level is too high, the excess oil gets splashed around inside the engine. It can work its way into the combustion chamber or soak the air filter. When it gets hot, it burns, producing that telltale white or bluish smoke.

If this turns out to be your problem, you're in luck, because the fix is quite easy. First, turn off the mower and let it cool down completely. Then, check the dipstick. If the oil level is above the "full" line, you need to drain some of it.

You can usually do this by tipping the mower on its side (make sure the carburetor and air filter are facing up to prevent more spills) and letting some oil run out of the fill tube. Drain a little at a time, rechecking the dipstick until it's at the proper level.

You Tipped the Mower the Wrong Way

Did you tip your mower over to clean the undercarriage or to check the blades? If so, which way did you tip it? Tipping a four-stroke engine mower the wrong way is a classic blunder. If you tilt it so the carburetor and air filter are facing down, oil can leak from the crankcase directly into these components.

When you start it up again, that leaked oil will burn off in the engine and exhaust, creating a plume of smoke. It might also soak the air filter, which can cause its own set of problems.

If this is the issue, the smoke will usually stop on its own after a few minutes of running as the spilled oil burns away. However, make sure you pause and check your air filter. If it's soaked with oil, it'll need to be replaced, as an oil-logged filter will restrict airflow to the engine and cause it to run poorly.

Worn Engine Components

If you haven't recently added oil or tipped the mower, and it consistently smokes every time you use it, you might be looking at a more serious internal engine problem. Over time, parts like piston rings or valve seals can wear out.

The piston rings are designed to create a seal, keeping oil in the crankcase and out of the combustion chamber. When they wear down, oil can seep past them and burn with the fuel, resulting in constant blue or white smoke while the engine is running. Similarly, a leaking head gasket can allow oil to enter the combustion chamber and lead to smoke.

While this problem is common, fixing worn internal engine components is a job for a professional, or at the very least, an extremely experienced DIYer. It involves taking the engine apart, which requires special tools and training, so if you suspect this is your issue, it's best to take your mower to a small engine repair shop.

Black Smoke

Seeing black smoke is a different story, as the dark color indicates that the engine is running "rich," which means it's burning too much gasoline and not getting enough air. The black color comes from carbon deposits produced by the partially burned fuel. There are a few things to check for if you're seeing black smoke:

A Clogged Air Filter

This is the simplest and most common cause of black smoke: your mower's engine needs to breathe. The air filter's job is to stop grass, dust, and other debris from getting inside. Over time, it gets clogged.

When the filter is dirty, it restricts the amount of air that can get into the carburetor. This throws off the delicate air-fuel mixture; the engine gets plenty of fuel but not enough oxygen to burn it completely. The result is poor performance, sputtering, and black smoke.

If this is your issue, the first step, as you may have guessed, is to check your air filter. If it's a paper filter and it looks dirty, give it a few taps to knock loose debris. If it's very dirty or oily, replace it. They aren't expensive, and a new filter can make a world of difference. If you have a foam filter, you can often wash it with soap and water, let it dry completely, and then re-oil it with special air filter oil.

Carburetor Problems

The carburetor is the heart of your mower's fuel system, responsible for mixing the perfect ratio of air and fuel before sending it to the engine. If the carburetor isn't working correctly, it can send too much fuel, causing the engine to run rich and produce black smoke.

This can happen if the choke is stuck in the closed position. The choke is designed to enrich the fuel mixture for cold starts. If it doesn't open back up as the engine warms up, it will continue to deliver a rich mixture. Other issues could be a malfunctioning float or a clogged jet inside the carburetor.

So, what should you do? First, check the choke linkage to make sure it's moving freely. Sometimes, a bit of cleaning and lubrication is all it needs. If that doesn't solve it, the carburetor needs to be thoroughly cleaned. Here's how to clean lawn mower carburetor.

What If It's Not Smoking But Smells Hot?

Sometimes, you might not see visible smoke, but instead, just smell something burning. This could be as simple as dried grass and leaves packaged around the hot muffler or engine block; as the engine heats up, the debris starts to smolder and stink.

Always make sure the top of your mower deck and the area around the engine are free of clippings and leaves. A quick brush-off before and after each use is a good habit, too.

Tired of the Smoke and Hassle?

Diagnosing and fixing a smoking lawn mower requires time. And it's a headache for many lawn owners.

It's a common problem if you own a gas lawnmower, so if you want to get rid of it, it's better to switch to a better option, a robotic lawn mower.

A robotic lawn mower, such as Navimow X390, is an electric mower. There is no gas, oil, or engine. It works on a rechargeable battery, so you don't need to worry about the smoke anymore. It requires minimal maintenance and is quite easy to handle for even beginner lawn owners.

It also mows your lawn automatically, saving your weekends. You can enjoy yourself with your family. You only need to set a schedule for the mower, and it will mow your lawn with perfection.

Check out more robotic lawm mowers from Navimow and select a suitable one for your lawn.

FAQs

How do I fix white smoke from my lawn mower?
If the reason for white smoke is overfilled oil reservoir, you can fix it by draining the excess oil. And if you have recently tilted the mower, then the smoke will go away in a few minutes if you keep the mower running. Other than that, you can check the air filter and carburetor to solve the issue.

Can I use my lawn mower if it's smoking?
If it's smoking continuously and the oil reservoir is not overfilled, you should stop and diagnose the issue first. Only in the case of tilting a mower, you can use it even if it is smoking, as the smoke will go away when the spilled oil is completely burned.

Why is my lawn mower blowing grey smoke?
Grey smoke is an indication of a worn-out engine. It happens when the engine consumes excessive oil. In this case, you should call a professional to get the mower fixed.