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8 Reasons Your Push Mower is Smoking: White, Blue, Black Smoke

Smoke coming from your lawn mower is alarming. You may be able to easily fix some smoking issues and keep them from developing into a severe problem. However, if you do have internal engine damage, it could mean you need professional help or you may need to purchase a new mower.

A push mower smokes when there is an insufficient oil level; oil spilled on the engine; a plugged air filter; an incorrect choke setting; a bad engine gasket; or a valve train or piston ring problem.

Follow all safety precautions outlined in your push mower operator’s manual to prevent injury. Take caution when working around a hot engine. Once you repair your smoking problem, allow your push mower to run for 10-15 minutes to burn off any remaining oil until the smoking stops.

Push mower is smoking

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing or operating. Consult a professional if you don’t have the skills, knowledge or are not in the condition to perform the repair safely.

Push Mower is Emitting White, Blue or Black Smoke

Black Smoke from a Push Mower

Black smoke is typically a sign of your engine running rich. This means a higher concentration of fuel to air is being burned in the cylinder. The things to look for when you see black smoke is a plugged air filter, an incorrect choke setting or another air flow restriction.

White or Blue Smoke from a Push Mower

White or blue smoke coming from your push mower is usually a sign your engine is burning oil. Follow the steps below to find reasons the mower starts burning oil including an incorrect engine oil level, worn piston rings, valve train problem, bad engine gasket or incorrect oil viscosity.

If you have a push mower running a two-cycle engine, the oil to fuel ratio may be incorrect. Refer to your owner’s manual for the correct mix for your model engine.

8 Reasons a Push Mower is Smoking

Air Filter is Plugged in a Push Mower

Mowing the lawn can be a dirty task with your mower tossing dirt and grass clippings in the air. The air filter is required to prevent this dirt and debris from entering the air intake and causing damage to the engine.

If the air filter is not cleaned regularly during the mowing season, it can become plugged and prevent clean air from passing through the filter. A reduced amount of air will cause your mower to run rich because the engine is getting a higher concentration of fuel mixed with air. This will cause your mower to emit a black smoke.

Another result of a plugged filter is oil in the cylinder. The engine requires air to run and when it can’t get it through the air filter, it may pull air out of the crankcase. Oil will also be pulled into the cylinder with this air and smoke as it burns in the hot cylinder.

I recommend starting each season out with installing a new air filter while you perform the annual maintenance on your push mower. Then, clean the filter a couple of times during the mowing season. Never run your push mower without an air filter even if it’s just until you can get a replacement filter.

Follow these instructions to clean your type of air filter:

Clean a push mower paper air filter

  • Remove the air filter from the air filter housing.
  • Wipe out any dirt remaining in the housing with a clean dry cloth. Don’t allow any dirt to fall into the air intake.
  • Tap the filter against a solid surface to knock loose and remove as much dirt as possible. Don’t use compressed air as it can damage the filter.
  • Hold up your filter to a light source to see if light is shining through the paper.
  • Reuse the filter if you do see light through the paper. Install a new filter if you cannot see light.
  • After you install your filter, reattach the filter housing cover.

Clean a push mower foam air filter

  • Remove the air filter for the air filter housing.
  • Wipe out any dirt remaining in the housing with a clean dry cloth. Don’t allow any dirt to fall into the air intake.
  • Inspect the filter. If it is brittle or has dark spots or tears, replace the filter with a new one.
  • If the filter appears to be in good condition, wash the filter with a mild dish soap and water to remove any dirt and oil in the filter. Rinse until clear.
  • Lay flat to dry. Laying out in the sun will help speed up the drying process.
  • Once completely dry, use a foam filter oil to lightly saturate the filter. The filter needs to be fully covered in oil, but you don’t want it to be dripping of oil. Squeeze excess from the filter. Perform this step if you are using a new foam filter.
  • Install the filter into the housing and secure the cover.

Incorrect Choke Setting on a Push Mower

A black smoke will come from your mower when the choke setting is not correct. If you have a manual choke and it sticks remaining in the choke position, lubricate the choke cable so it moves freely and no longer sticks. If you have a an automatic choke that is no longer functioning correcting, it’s best to have your local lawn mower repair shop repair the problem.

Tipped Push Mower

Using your push mower on a hillside or tipping the mower causing engine oil to run onto the air filter and carburetor with make your it smoke. Check the air filter and replace it with a new filter if it is covered in oil. Before installing the new filter, wipe out any oil you find in the air filter housing. Clean the carburetor.

Low Engine Oil Level on a Push Mower

You may have not put enough oil in the crankcase when you completed your last oil change. It could be you are using the wrong oil viscosity or you have developed an oil leak leaving you with a low engine oil level.

Having a low engine oil level in the crankcase will not provide the lubrication needed for the internal engine parts to move freely. Friction will begin to build increasing the heat. This heat can become so intense that the oil begins to burn and smoke. The engine parts may also begin to melt.

If a low oil level is the reason your push mower is smoking, you can attempt to correct the problem by adding fresh oil. Most likely, this will not help. If your mower started smoking because of a low oil problem, you probably causes significant engine damage.

Bring your mower to your local small engine mechanic to be diagnosed. You will then need to make the decision to perform the engine repair or replace your push mower.

Too Much Oil in a Push Mower

Filling your push mower with too much engine oil can increase the pressure in the crankcase. This can cause oil to get pushed into the cylinder or even up to the air intake through the valve train. Oil will begin to burn off when the engine gets hot and emit a smoke.

Replace the air filter if you find it covered with oil. Next, correct the engine oil level to bring it to the full level as indicated on your oil dipstick. You can remove a little oil by quickly removing and replacing the drain plug.

If your mower doesn’t have a drain plug, tip the mower on its side to remove a little oil from the oil fill area. Keep the air filter and carburetor on the high side of the mower when tipping it.

I prefer to use a turkey baster, like the one in your kitchen, or an oil evacuator to suck a little oil out of the oil fill area. To me, this is the easiest and cleanest method.

Bad Engine Gasket on a Push Mower

A failing gasket can cause oil to leak from the engine. This oil will begin to smoke when it burns off the hot engine or muffler. You must locate the bad gasket and replace it. The difficulty of this task depends on the location of the failed gasket.

Piston Ring Problem in a Push Mower

A quick check you can perform that may indicate you have an internal engine problem is looking for oil on the spark plug. When you find oil on the spark plug, I advise you take the push mower to an experienced small engine mechanic for diagnosis.

Excessive oil on the spark plug indicates you may have a piston ring or valve train problem. Either problem will result in having to take the engine apart. You may find a scoring inside of the cylinder wall or worn rings causing oil to enter the combustion chamber and burning off.

If you have this type of problem, you may have to make the choice between replacing your engine or buying a new mower.

Valve Train Problem in a Push Mower

A valve train problem is not always the worse problem to have. The only way to detect this is by removing the cylinder head and performing a leak down test. This should be performed by an experienced mechanic.

A problem with the valve train can develop when the valve gets burned by being overheated. The heat can cause the edge of the valve to fall apart. This is known as a burnt valve. An indication you have a burnt valve or timing problem is a muffler that is glowing red due to extreme heat.

The valve and seat will have to be cut at certain angles to make sure the valve seats correctly. It needs to make good contact with the engine block to complete the combustion chamber.

Still Having Problems with Your Push Mower?

There are many common problems push mower owners encounter over a mower’s lifespan. Every mower develops problems over its lifespan even when purchasing the top of the line mower. To help you identify causes of these problems and how to fix them, I put together this guide to help: Common Push Mower Problems & Solutions.