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Why Is My Lawn Mower Smoking? Common Causes and Fixes

AZparts Team

Updated on June 13, 2025

10 min read

Seeing smoke rise from your lawn mower can be unsettling, but do not panic just yet. Whether it is a harmless case of spilled oil or a sign of a more serious issue, understanding the cause is the first step to a fix. From clogged air filters to engine overload, even electric mowers are not immune. AZParts will guide you through the diagnosis and provide the reliable parts you need to restore your mower’s power and performance. Get back to a clean, even cut with no smoke in sight.

1. Identify the Smoke Type Appearing on Lawn Mower

A simple way to diagnose lawn mower problems by color (Source: AZParts)

When your lawn mower starts to smoke, don’t panic. The first thing you need to do is check what color the smoke is. This small step will help you figure out exactly what’s wrong.

White Smoke

This is the most common type of smoke. It usually means that oil has made its way into parts of the engine where it shouldn’t be, and now it’s burning. This often happens when:

You put too much oil into the engine.
You tipped the mower sideways the wrong way (the oil spills into the muffler or air filter).
Oil leaked internally into the combustion chamber.

White smoke may look scary, but most of the time, it’s harmless and easy to fix.

Blue Smoke

Blue smoke is very similar to white smoke. It’s also caused by burning oil, but it usually means the engine is hotter or the oil leak is more serious. You may see this if:

The engine is old and the internal parts are worn out.
Seals or rings inside the engine are damaged.

If your mower blows blue smoke consistently, it might need more than a quick fix.

Black Smoke

Black smoke is different—it means your mower is burning too much fuel. This often points to a problem with the air and fuel balance inside the engine. Common causes include:

A clogged air filter so not enough air is getting in.
The choke is stuck on, letting too much fuel into the engine.
The carburetor is dirty or misadjusted.

Black smoke usually means the engine is working too hard and needs some cleaning or adjustment.

2. Common Causes of Lawn Mower Smoking

Now that you’ve checked the smoke color, let’s go over the main reasons why lawn mowers start smoking. These are easy to check and understand, even if you're not a mechanic.

Overfilled Oil

When you pour too much oil into the mower, it doesn’t just stay in the reservoir. It can splash into the muffler, air filter, or cylinder. Once that oil burns, it turns into white or blue smoke. This is especially common after a recent oil change.

How to tell: Check the oil dipstick. If the oil line is above the “Full” mark, you’ve added too much.

Dirty or Clogged Air Filter

Clogged Air Filter Causes Black Smoke (Source: AZParts)

The air filter lets clean air into the engine. If it’s full of dust or grass, the engine gets less air and burns more fuel than it should. That’s what causes black smoke.

How to tell: Open the air filter cover and check the filter. If it’s dark, dusty, or oily, it needs cleaning or replacement.

Old or Stale Fuel

Fuel that’s been sitting in the tank for more than a month can break down. It doesn’t burn cleanly, and this can make the engine smoke or run poorly.

How to tell: You filled the tank a while ago and didn’t add a fuel stabilizer. The mower may be hard to start and blow white or grey smoke.

Worn Spark Plug

A spark plug helps the engine ignite fuel. If it’s worn out or covered in black soot or oil, it can’t spark well—leading to incomplete burning and smoke.

How to tell: Remove the plug and look at the tip. If it’s black, oily, or damaged, it needs replacing.

Leaking Gaskets or Damaged Piston Rings

Persistent smoke and oil leaks may point to worn engine seals (Source:AZParts)

Inside the engine, seals called gaskets and rings keep oil in place. If they’re worn out, oil leaks into the part of the engine that burns fuel—causing thick white or blue smoke.

How to tell: Smoke keeps coming even after all other fixes. The mower feels weak or runs rough. You may also see oil leaks on the engine.

3. How to Fix a Smoking Lawn Mower

3.1 Quick Fixes

Fast Fixes for Lawn Mower Smoke Problems (Source: AZParts)

If your mower starts smoking, begin with these fast troubleshooting steps:

Turn Off and Let It Cool: Shut off the engine immediately. This is crucial for your safety. Allow the mower to sit for at least 30–60 minutes before inspecting.
Disconnect Power (Electric Models): If you’re using an electric mower, remove the spark plug or disconnect the power source to prevent any accidental startups.
Check the Oil Level: Use the dipstick to verify the oil level. If it’s too high, carefully drain the excess until it reaches the correct mark. Also, check the oil’s condition-dark, sludgy oil should be replaced.
Inspect the Air Filter: Remove the air filter and check for buildup. If it’s clogged with dirt or soaked in oil, clean it with soap and water (if reusable) or replace it.
Run the Engine Briefly (If Safe): Once you’ve completed the above steps and ensured there are no leaks, restart the mower and let it run for 5–10 minutes. This may burn off any oil that enters the combustion area.
Monitor the Smoke: If the smoke clears within a few minutes, the issue was likely minor. If it persists or worsens, continue to detail fixes or consult a technician.

3.2 Detailed Fixes

For persistent smoking or internal issues, follow these more advanced steps:

Drain and Refill Engine Oil: Use the recommended oil type and amount for your specific mower model. Old or incorrect oil can lead to continued smoking.
Clean the Carburetor: A dirty carburetor can throw off the fuel/air mixture. Remove it carefully and clean it with a carburetor cleaner to remove any gunk or debris.
Replace the Spark Plug: A fouled or worn spark plug causes poor combustion. Swap it out for a new one if necessary.
Inspect for Internal Leaks: Persistent smoke could mean worn piston rings, a cracked gasket, or valve seal problems. These typically require professional diagnostics and repair

Before you move on to deeper fixes or contact a repair service, take a look at this summary chart to match the smoke color with common causes and solutions.

Quick Recap: Smoke Colors and What They Mean

Smoke Color	Common Causes	Severity	Common Fixes
White/Blue	Overfilled oil, tipping, spilled oil, worn piston rings	Low to High	Adjust oil, clean parts, replace spark plug, repair
Black	Dirty air filter, rich fuel mix, carburetor or choke problems	Low to Medium	Clean/replace filter, tune carburetor
Grey	Blown head gasket, engine wear	High	Professional repair or engine replacement

4. How to Prevent Lawn Mower Smoke in the Future

Smoke from your lawn mower isn’t just annoying; it’s a sign your machine needs attention. Thankfully, with a few simple steps, you can keep your mower running clean and smoke-free for years to come:

Always Check the Oil Before You Mow

Engine oil plays a vital role in keeping internal parts lubricated and cool.

Use the dipstick to check the oil level before each use.
Avoid both low oil (which causes friction and overheating) and overfilling (which leads to oil burning and blue smoke).
Replace old oil with the manufacturer-recommended type to ensure optimal performance.

Clean or Replace the Air Filter

A dirty air filter restricts airflow, which causes incomplete combustion and smoke.

Inspect the filter every 3–4 weeks, especially in dry or dusty areas.
Replace foam or paper filters as needed. It’s a low-cost fix that can prevent costly damage.

Use Fresh, Clean Gasoline

Refueling with Fresh Gasoline for Optimal Lawn Mower Performance (Source: AZParts)

Old or contaminated gas is one of the leading causes of starting issues and poor combustion.

Never leave fuel in the tank for more than 30 days.
Use a fuel stabilizer if storing the mower for long periods.
Drain the tank before winter storage to avoid build-up and gumming.

Tip the Mower the Right Way

Improper tilting during cleaning can send oil into the carburetor or air filter, causing white or blue smoke when restarted.

Always tip the mower with the air filter or carburetor facing up.
Let the mower sit for a while if accidentally tilted the wrong way, then clean any oil-contaminated parts.

Perform Seasonal Maintenance

At the start of each mowing season, change the oil, clean the air filter, replace the spark plug, and inspect the blades. This keeps your mower in great shape. If you need a new air filter, spark plug, or carburetor. AZParts has the right parts for your mower. Our products are high quality, affordable, and easy to install.

Bonus Tip: Create a seasonal maintenance checklist. Hang it in your garage or shed and mark off tasks as you complete them. Staying proactive is the easiest way to prevent smoke and ensure your lawn mower stays reliable, season after season.

Seasonal Maintenance Checklist

Season	Recommended Maintenance Tasks
Spring	• Change engine oil • Install new spark plug • Clean or replace air filter • Drain old winter fuel and refill with fresh gas. If the valve is worn, replace it with Cut-Off Fuel Gas Valve. • Sharpen and balance mower blade
Summer	• Check air filter every 2 weeks • Monitor engine temperature • Clear grass buildup under the deck • Clean mower’s exterior to prevent clogging
Fall	• Drain fuel or add stabilizer • Deep-clean the mower. After cleaning, inspect primer base; replace if worn with Air Cleaner Primer Base • Remove battery for electric models • Store the mower in a dry, sheltered area using a lawn mower cover to prevent dust and moisture.

5. FAQs about Lawn Mower Smoking

5.1. What to do if a lawn mower is smoking?

First, turn off the engine immediately to prevent further damage or fire risk. Let the mower cool for 15–30 minutes.
Then check:

Oil level using the dipstick: overfilled or low oil can both cause problems.
Remove the air filter and inspect it for dirt or oil clogging.
On the underside of the mower, look for grass buildup or oil leaks.

Fix simple issues (like cleaning the air filter or draining excess oil), and restart the mower in a well-ventilated area. If the smoke continues, stop using the mower and inspect further.

5.2. Why is my lawn mower blowing grey smoke?

Grey smoke often signals a serious internal engine issue , such as

A blown head gasket
Worn piston rings
Crankcase pressure issues

It may also occur if the oil is extremely old or contaminated.
Grey smoke usually comes with other signs like oil leaks, reduced power, or rough operation.
If you see grey smoke, it’s best to take the mower to a repair technician to avoid permanent damage.

5.3. Will low oil cause a lawn mower to smoke?

Low oil won’t directly cause smoke, but it can lead to:

Overheating, which may cause components to expand or fail
Engine wear that lets oil leak into the combustion chamber, creating smoke

In some cases, overheating can warp the head gasket, which results in oil leaking into the piston area and leads to white or blue smoke.

Always check the oil before every mow to keep your engine healthy.

5.4. How do I know if my lawn mower has a blown head gasket?

A blown head gasket can cause:

White or grey smoke from the exhaust
Loss of power
Oil leaking around the engine block
Milky oil (a sign that coolant or fuel has mixed with oil)

If your mower shows two or more of these signs, stop running it.

A blown gasket should be repaired by a professional.

5.5. How do I know if my lawn mower engine is blown?

A blown engine usually shows:

Constant or thick white, blue, or grey smoke
Loud knocking sounds or grinding
Oil leakage
Engine won’t start or quickly stalls after starting

In most cases, the repair cost exceeds the value of the mower.
If your mower engine is blown, consider replacing the engine or investing in a new mower.

5.6. How to fix black smoke from the lawn mower?

Black smoke means too much fuel is being burned, often due to:

Clogged air filter (not enough air)
Stuck choke in ON position
Carburetor running rich

To fix:

Clean or replace the air filter
Check the choke lever to make sure it’s off after starting
Adjust or clean the carburetor to ensure proper fuel mi

After fixing, let the engine run for a few minutes to clear leftover smoke.

Lawn mower smoking is a common issue, but with proper maintenance, it can be avoided. Regular oil checks, clean air filters, and seasonal care keep your mower running smoothly. For quality replacement parts, AZParts offers everything you need to maintain performance and prevent smoke.

Contact Information:

8 The Green, Ste A, Dover, Delaware 19901-3618, United States

support@azparts.com

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