Solved! This is Why Your Riding Mower is Smoking

A cloud of smoke is coming out of your mower and you get a little nervous. Smoke leads you to believe you are in for an expensive repair. That is not always the case.

Some items causing your mower to smoke can be easily found and fixed. However, there are items that will be more costly. When your problem isn’t caught early, you risk a large repair bill up to the cost of an engine replacement.

A riding lawn mower may smoke when the air filter is clogged, oil is burning off a hot surface or the oil level is incorrect. Smoking may also be the result of an internal engine issue including valve train or piston ring problems.

I’ll share what you need on your mower to identify the cause of your mower’s smoke.

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

Reasons Why Your Riding Lawn Mower Smokes: White, Black, Blue Smoke

Clogged Air Filter

The air filter must be kept clean because your mower requires clean air to run. Mowing conditions can often be very dirty with your mower kicking up dirt and grass clippings. This can plug your air filter restricting airflow.

When your mower isn’t able to get the air it needs, it can cause your engine to run rich emitting black smoke. Running rich means the engine is burning more gasoline than air.

Smoke can also be caused when the engine pulls air and oil out of the crankcase when it isn’t able to find air through the air intake due to the plugged filter.

A clean air filter is essential to keeping your lawn mower running at its best. Replace your air filter annually during your routine riding mower maintenance.

Check and clean it several times during the mowing season. The dustier your mowing conditions, the more often you need to check, clean, and replace your air filter.

Steps to clean your PAPER air filter element

• Remove the air filter from the housing.
• Remove any dirt that remains in the housing with a clean dry cloth. Make sure you don’t allow any dirt to fall into the air intake.
• Tap your air filter against a solid surface to loosen and knock out as much dirt as possible.
• With the filter held up to a light source, check for light shining through the paper. Reuse your paper when you can see light and replace it with a new filter when you cannot.

Never run your mower without an air filter, even if it is temporary. Any dirt or debris that gets into the engine can damage it. This can result in a significant repair bill.

Insufficient Engine Oil Level

The dipstick has markings on it to use as a reference for your engine oil level. The engine oil level must be at the full level. It is important the oil level is not higher or lower than required.

This is one of the items you want to make sure is just right. If you don’t, you can run into engine problems that will cause your riding mower to smoke.

Low Engine Oil Level

When there isn’t enough engine oil in the crankcase, the parts in your engine don’t receive the lubrication they require. This lack of lubrication can cause increased friction building heat.

This heat can become so hot, the parts begin to melt and the oil begins to burn off creating smoke.

Low oil and high temperatures in your engine are not good situations to have. You can try to add oil to bring it to the correct level, but it most likely will not solve your problem.

By the time your engine oil starts smoking because you have a lack of oil, there has already been significant internal damage. The extent of the damage should be diagnosed by a qualified small engine mechanic.

High Engine Oil Level

Too much engine oil can build increased pressure in the crankcase. This pressure pushes oil into your cylinder and up into the air intake through the valve train. When your mower runs for a while and gets hot, the oil burns off in the cylinder and creates smoke.

Make sure to check your air filter. This smoke can plug the filter or oil can get onto your filter. Replace your air filter if you find either one of these items. You will need to correct the engine oil level to bring it to the level recommended by your engine manufacturer.

There are several ways you can remove a little engine oil. You can remove it through the drain plug and engine oil filter.

You can also use an oil evacuator or turkey baster to remove some oil from the oil fill area. Once you have removed a little oil, recheck the level using your dipstick. Remove or add oil as necessary.

Bad Engine Gasket

Oil leaking onto a hot engine or muffler can cause your riding mower to smoke when the oil burns off. Look over your mower for oil leaks. This could be due to a bad gasket on your engine. Find the failing gasket and replace it to stop the leak.

Note: Oil spilled when changing your oil can cause smoking. You’ll want to make sure your smoke isn’t coming from a spill before you start searching for a failed gasket.

Piston Ring Problem

Once you have checked your air filter and engine oil level; and ensured you don’t have any engine oil leaks, move on to identifying whether your problem is a more severe internal problem.

While there is a simple troubleshooting step that can be performed that could indicate an internal problem in the engine, it is not one that can point to the actual cause of the internal problem.

To narrow it down to the specific problem, you will need a qualified small engine mechanic to perform further diagnostics.

For this troubleshooting step, you will be checking for oil on the spark plugs. To do this, use a 3/4” or 5/8” socket, depending on your engine model, to remove your spark plug. If you find oil on your spark plug, this could indicate you have a piston ring or valve train problem.

An engine mechanic will need to tear down and check the engine. The mechanic may find scoring on the cylinder wall which is allowing oil to enter the combustion chamber. This oil begins emitting smoke once it gets hot and begins to burn off.

Valve Train Problem

A burnt valve in your valve train can cause your riding mower to smoke. A burnt valve is a valve that has been overheated. An extremely hot muffler can indicate you have a burnt valve or timing problem.

The only way to truly confirm a valve problem is to remove the cylinder head and perform a leak-down test. This test and repair should be performed by a small engine mechanic.

If the mechanic finds a burnt valve, the valve and seat will have to be cut at certain angles so it is seated correctly. This repair must be performed correctly to complete the engine combustion chamber.

Difference Between White, Black & Blue Smoke

While the color of the smoke should not be a replacement for the steps above, it can be used in combination with the steps to help confirm your findings and give you a good place to start troubleshooting.

Black Smoke

This color usually is due to your engine running very rich. Running rich is when more fuel is being burned than air.

Check your air filter for air restrictions. If this isn’t your problem, check for other airflow restrictions including a stuck choke.

Blue or White Smoke

This color of smoke is due to the burning of excess oil. It is best to follow the steps above to identify the root cause starting with checking the engine oil level followed by checking for damage to the piston rings, valve train, or engine gasket.

You invested a considerable amount of money into your lawn mower. Checking your engine oil level and air filter before each mowing could prevent costly repairs.