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Why Your Toro Lawn Mower is Smoking

The first sign of smoke from your Toro lawn mower can be alarming. Signs of smoke could be a simple fix or it may be an indication you have a severe problem that could result in needing a new engine. The age of your engine and how well it has been taken care of can have a direct correlation to your engine problems.

A Toro Lawn Mower may smoke because of an insufficient oil level or air flow restriction. Smoke can also develop from oil burning in the combustion chamber or on the muffler due to piston ring, valve train or gasket failure in your engine.

Start with looking at potential problems that are the easiest to check and move on to the move difficult internal engine problems.

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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.

Reasons Why Your Toro Lawn Mower May Be Smoking

Toro Lawn Mower Air Filter is Plugged

Your Toro uses an air filter to keep dirt and debris from entering the engine so only clean air is being allowed into the air intake. When the air filter is plugged full of dirt and grass, the engine is no longer able to gain access to air. Your engine can overheat, and worse yet, begin to pull air and oil out of the crankcase. The air that gets pulled out of the crankcase begins to burn causing a smoke.

Check your air filter more frequently than just doing so during your standard lawn mower service. Keeping your filter clean can save you from a large engine repair bill in the future.

Clean your air filter using the following steps:

  • Remove the air filter cover. Depending on the type of mower and style air filter you have, the cover will usually have one or two thumbscrews or knobs holding it down.
  • Remove your air filter from the filter housing. Be careful when removing so you don’t knock loose dirt into the air intake. Wipe any dirt remaining in the housing with a dry clean cloth.
  • If you have a paper air filter, knock the dirt out of the filter by tapping it against a hard surface until all the loose dirt has been removed. Never use compressed air to blow out the dirt.
  • Hold the air filter up to the light to check for light shining through the paper filter. If you are unable to see light through the paper, you must replace your filter.

If your lawn mower is using a different type of filter, read my article explaining how to clean different types of filters.

Insufficient Engine Oil Level in Your Toro Lawn Mower

An engine in your Toro lawn mower without the amount of engine oil recommended by the engine manufacturer can cause your mower to smoke. It does not matter if the oil is too high or too low because both can result in smoking.

  • Toro Has a Low Engine Oil Level
    When you have an engine oil level that is too low, the moving parts no longer have the sufficient lubrication. Friction caused by the working engine parts increases causing your engine to build extreme heat. This heat causes the components of the engine to melt and smoke.

    You can attempt to add fresh engine oil to your engine to try to salvage it. Most of the time, once it reaches this point, adding additional oil won’t help because the heat already caused extensive engine damage. You need to bring your mower to a Toro dealer to be looked at.

    Toro Has a High Engine Oil Level
    Having too much oil can cause too much crankcase pressure which causes oil to get back into the cylinder or even up to the air intake through the valve train. In this case, the oil is getting into the cylinder and begins to burn off when the engine gets hot creating a smoke. You need to drain some oil out of the engine to resolve this problem.

Piston Ring Problem in Your Toro Lawn Mower

Once you get to this step, you are looking to see if you might have internal engine damage causing your Toro to smoke. Once you identify you have a larger internal engine problem, you should take your lawn mower to a mechanic who has experience working with small engines if you are not mechanically inclined.

One way that could indicate you have an internal engine problem is checking for oil on the spark plug. Remove the spark plug. You’ll need a 3/4″ or 5/8″ socket, depending on the mower you own. Pull out the spark plug and check for excessive oil buildup. If you find oil, it’s a sign you have an internal problem.

Excessive oil on the spark plug indicates you may have a piston ring or valve train problem. Either problem will result in you having to take the engine apart. You may find a scoring inside of the cylinder wall 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 Your Toro Lawn Mower

You may have a valve train problem. This is not always the worse problem to have. The only way to detect this is by removing the cylinder head and preforming a leak down test. This should be completed by a small engine mechanic.

You can develop a valve train problem when the valve gets burned by being overheated. The heat cause the edge of the valve to fall apart. This is what is known as a burnt valve. If your muffler is glowing red due to extreme heat, this can also be indication your Toro has a burnt valve or timing problem.

The valve and seat will have to be cut at certain angles to make the valve seat correctly. This is so it makes good contact with the engine block to complete the combustion chamber.

Bad Engine Gasket in Your Toro Lawn Mower

A Toro mower with a bad engine gasket may leak oil onto the hot muffler. A smoke is created when the oil burns from the heat of the muffler. You must locate the bad gasket and replace it which can be pretty difficult depending on the location of the gasket.

Difference Between Blue, White and Black Smoke in Your Toro Lawn Mower’s Engine

I recommend going through the list above to identify your smoking problem. However, the color of smoke can give you a clue as to what area on your mower you need to focus on.

  • Black Smoke – This color usually is due to the engine running very rich. This is when there is more fuel being burned than air so the first thing to check is the air filter and clean or replace. If this isn’t the issue check for another air flow restriction.
  • Blue or White Smoke – This color smoke is due to burning 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 of the piston rings, valve train or engine gasket.

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