Why a Lawn Mower Blows White Smoke — Causes & Easy Fixes

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From my years specializing in lawn care, I’ve seen many homeowners panic when their lawn mower begins puffing white smoke. While it’s understandable to be worried about possible repair costs, often you can troubleshoot underlying issues on your own without calling in an expert.

Let me walk you through the potential reasons behind this and offer some simple solutions to get your mower back up and running smoothly.

Cause #1: Tipped-Over Lawn Mowers

One of the common perpetrators of white smoke is tipped-over lawnmowers. Tipping the mower will cause oil to overflow or reach beyond the dipstick level. Observe your mower and check if it was tipped off at a very steep angle. 

removing oil on a lawn mower

If stored at an angle of more than 15, it will lead to white smoke coming from your lawn mower. This can also happen by accident, cleaning the chute or emptying the decks. 

This causes the oil to move from the crankcase to the cylinder block, causing the lawnmower to produce white smoke and prompt oil leaks. 

How to Fix Your Tipped-Over Mower

To fix a tipped-over mower, position it upright, and check the oil in the gas tank or crankcase before running the engine. Let the engine idle until all the smoke is gone. 

It may be a simple solution to your lawn mower smoking, but you’ll still experience smokes rummaging, so it’s best to advise your neighbors to avoid any future complaints. 

Cause #2: Oil Overfilling the Engine

A general lawnmower has very little space and container for oil, so, commonly, the crankcase gets overfilled now and then. Check the oil level before mowing again to prevent overfilling the gas tank. 

mower dipstick showing oil overflow

Most people assume that a little oil or too much oil is okay, but this cannot be good for most engines. If the oil engine is higher than the splash paddle, the engines won’t work. 

It’s also ideal for observing the smell coming from your engine because when the oil starts to smell like gas, it can indicate a broken carburetor. To quicken the process, extract the excess oil immediately, and ensure you clean your carburetor regularly. 

How to Fix Engine Oil Overfill

Turn your engine over and gently flip it to spill the oil away. Replace the plug and follow the detailed measures of carburetor cleaning and replacing the worn-out air filter. A normal lawnmower doesn’t need more than 20 ounces of engine oil, so keep this figure in mind. 

Use a dipstick to measure the oil level, and observe whether you should drain or pour some of it to avoid overspilling. For more tips, check this guide to know how much oil should you put in your lawn mower. 

Cause #3: Piston Rings are Faulty

A failed piston ring is one of the worst reasons your tractor mower is blowing white smoke. If the lawnmower isn’t maintained properly, chances are it will cause failed piston rings and prompt excess oil in the combustion chambers. 

mower piston ring repair

Piston rings keep the mower’s engine oil intact, and it gets damaged due to a dirty air filter or dirty engine oils. 

How to Fix Faulty Piston Rings

Faulty piston rings are almost an end game. It will require a complete overhaul, and opening the whole engine is necessary. 

Damaged rings will also cause damage to the head cylinder and head gasket, so you’ll have to replace them too. Tapping professional help is best to prevent trouble when fixing your rings. 

Cause #4: Leaking or Broken Head Gasket

Another serious reason for a lawn mower’s white smoke is faulty head gaskets. Head gasket failure is a little more complicated problem than the aforementioned reasons above. Head gaskets are seals used to keep a fast engine. 

repairing mower blown gasket

You can find it in the area joining the cylinder and the rest of the engine. When your gaskets are damaged, the engine will produce white smoke. Oil leaks and high crankcase pressures are also common due to faulty head gaskets.  

How To Fix the Head Gasket's Leak/Damage

The only possible way to fix a head gasket failure is to replace it because repairing it is not an option. It’s not expensive, so it’s an easy fix. 

Step 1: Get a Head Gasket Replacement

Grab a replacement gasket from your local dealer or purchase it online. Make sure you buy the same gasket type because there are a lot of options available, and it’s not a one-size-fits-all type. 

Step 2: Detach the Cylinder Head

Pull out the sparkplug wire and detach the bolts that keep the cylinder attached to the engine block. 

Step 3: Detach the Gasket

Look for the gasket on the engine block and remove it with a tool. Be careful when removing the gasket pieces to avoid roughing out the smooth surface while scraping the debris. 

detaching gasket

Step 4: Install the New Gasket

Your new gasket should fit in perfectly with your engine block. Install the new cylinder head before realigning the sparkplug wire. 

Check if Your Mower Has an Overhead Valve Engine

I’ve always advised homeowners to get to know their mower’s engine before diving into any repairs. Check to see if it has overhead-valve engines before you consider taking it apart.

For a bit of clarity, engines with overhead valves have their valves and cylinders positioned above the combustion chamber. If not, then the valves are situated below the combustion chamber. It’s these small details that can make this task easier.

Cause #5: Oil Spilled on the Fuel Tank (Applicable to 4-Stroke Lawn Mowers)

Never mix oil and mower fuel if you own a 4-stroke lawnmower. Most lawnmower models available in the market now come with a 4-strokes engine, making them more reliable than the traditional 2-stroke ones. It’s also less difficult to maintain, but mixing oil will cause a serious issue. 

mower oil leak

Once they infuse inside the lawnmower, the oil will start burning, causing smoke while running. It’s also a perpetrator of premature engine wearing. 

How to Fix Oil in the Fuel Tank

To fix the oil in the fuel tank and avoid smoke, the only way is to burn off the contaminated gas by letting the mower run and then replacing it with clean and fresh gas. You will experience white smoke coming out from the mower until it’s able to exhaust all the oil burnt.

But if you’re not comfortable with this fix, you can remove the fuel by detaching the fuel tank and filling it out with a new and clean one.  

Step 1: Search for the Fuel Line

Look for your mower’s carburetor and search for the fuel line and fuel tank. This part of the engine is what feeds fuel into the engine. 

Step 2: Detach the Fuel Line

Undo the clip that connects the fuel line and maintains its hold. Pull the fuel line off, and unplug the connection from the fuel line to the shut-off valve. The shut-off valve stops the fuel flow to the engine. 

unlinking fuel line

Step 3: Gather the Spilled Oil/Gas

Once you have removed the fuel line, the fuel will start to pour and collect with a pain to avoid engine oil spillage, which will be more difficult to clean. It’s also a fire hazard, so be careful about spilling oil over the floor. 

Step 4: Empty the Carburetor

Search for the carburetor and drain the fuel coming out from it. The carburetor of lawnmowers is located underneath, containing a tiny nut or screw used to empty the carburetor. 

Extra Tips

Check the Tank for Stuck Oil/Gas

From my time in lawn care, I’ve seen how stuck oil and gas can wreak havoc on an engine. To prevent any issues while running your machine, always ensure your fuel tank is clean. I personally recommend using a mixture of dishwashing liquid poured directly into the fuel tank.

Give that fuel or gas tank a good shake, making sure you dislodge any trapped oil and gas. If you’re looking for another option, a carburetor cleaner works wonders too. Remember, a clean machine runs better and lasts longer.

Don't Tilt Your Mower

Tilting the mower can result in oil spilling into the carburetor or cylinder, so I highly suggest avoiding this from happening, as this can cause damage to your machine. 

lawn mower on the ground

Other Probable Reasons Why Lawn Mowers are Blowing White Smoke

While I have common reasons here, dealing with a defective mower is tricky since many factors can be at fault. 

Faulty Carburetor Seal

Another perpetrator of lawn mowers producing white smoke is failed carburetor seals. If this happens, do not run the engine. If there’s an overfilled oil level, chances are it will thin the oil and make the machine vulnerable. Change the oil after repairing the carburetor. 

Oil Problems

Using the wrong type of oil is a critical mistake you would want to avoid, whether working with a lawn tractor, riding a mower, or other machines. Oil problems can cause unnecessary damage to your engine, and white smokes are another possible repercussion. 

Tilted Engine

Do not tilt your lawnmower, as this is the most common reason for white smoke. It is important to ensure that the lawn mower’s engine is level and properly positioned. Keep it at an angle not bigger than 15 degrees to avoid such. 

Broken Parts

It’s common for most parts to wear out, especially if you’re frequently using it. Such parts may include the head gasket and cylinders, so checking these parts regularly is ideal. 

fix mower engine

Less Common Reasons

Apart from the common reasons for the smoke I’ve mentioned above, here are other possible reasons why white smoke comes from your lawn mower.

Why a Lawn Mower Blows White Smoke and Die

One cause of lawnmowers blowing or releasing white smoke is excessive oil getting into the carburetor. It will die when the gas feed jet is blocked, which is a usual effect of overfilled oil. 

A dirty carburetor can also be a culprit for your mower blowing white smoke. Also, here’s why your lawn mower starts then dies, plus troubleshooting tips. 

Is White Smoke a Sign of Lawn Mower Problems?

White smoke is common, resulting from many common occurrences while using your lawn mower. If you’re a regular user, then this should not scare you. But regardless of what’s causing it, relevant fixes are apt for each case.

White Smoke + Burning Oil

white smoke from mower

One common culprit behind white smoke I’ve come across is burning oil. Always consult and study your owner’s manual closely to understand the correct oil level for your machine [1]; overfilling can be just as detrimental as burning the oil. 

To help you out, let’s delve into the common causes:

Why Do Electric Mowers Smoke?

Do not attempt to use your riding mower if it’s smoking (especially black smoke). Unplug immediately and check the motor because it’s more likely to have burnt out. 

mower releasing white smoke

There are also cases where the electric mower has a belt to drive the blade, and it’s what has been causing the smoke all along. Other common symptoms for smokes are the following:

Conclusion

From putting too much oil, a faulty mower’s engine, a clogged air filter, or just leaving your mower on its side when you did maintenance, I’ve tackled all the possible reasons why your lawn mower emits white smoke. 

While the fix is simple, being cautious when your mower shows signs of a problem will save you from ruining the engine. I hope this guide makes troubleshooting a lot easier!

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Robert Johnson is a passionate furniture maker & carpenter, sought after for his knowledge on the craft.
You’ve probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.

Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.

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