Why Your Cub Cadet Lawn Mower is Smoking

The first sign of smoke from your Cub Cadet lawn mower can be worrisome. Immediately you assume the worse with a very expensive repair ahead. Routine maintenance of your lawn mower engine can keep your engine from smoking. It may not be as bad as you think. It could be an easy fix.

Your Cub Cadet lawn mower may be smoking because the engine’s air filter system is plugged, there is an inefficient engine oil level; the engine may have a piston or valve train problem, or the engine gasket is bad.

Read on and I’ll take you through the steps of identifying the reason your Cub Cadet engine is smoking. It is best to start with the easiest items to check and rule them out as the problem. Then continue to move on to the more difficult diagnostic steps

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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, or knowledge or are not in the condition to perform the repair safely.

Reasons Why Your Cub Cadet Lawn Mower Is Smoking

1. Air Filter System is Plugged in Your Cub Cadet

So if my Cub Cadet engine was smoking the first thing I would do is check the air filter system. This is the easiest thing to check so why not start there?

• First, remove the air filter cover. The cover is always located above the carburetor so that it can pull in clean air. Depending on the type of mower you have, the cover usually has a single screw or two knobs holding it down. Some air filters will be along the side of the engine next to the carburetor.
• Remove the air filter. Be very careful to prevent dirt from dropping into the air intake. Wipe out any remaining loose dirt with a clean dry cloth.
• Take a look at your filter. If your air filter is plugged with grass and dirt, the engine will not be able to breathe. This can cause your engine to overheat. Your engine will be searching for air wherever it can find it. If it can’t get clean air through the air filter, it may begin to pull air and oil out of the crankcase.

  Your Cub Cadet will begin to smoke because of the oil that is burning off.

• Replace your air filter if it looks bad. Otherwise, knock the loose dirt out of the filter and place it back in the air filter housing. A good way to verify whether your filter can continue to be used is by holding the filter up to the light and checking to see if you can see light through the paper filter. If you can’t see the light or the filter is damaged you need to replace it.

To find cleaning instructions for other types of filters, you can read my article on different types of air filters and how to care for them. You can find many common air filters for Cub Cadet lawn mowers online at Amazon.

2. Insufficient Engine Oil Level in Your Cub Cadet

The level of engine oil in your Cub Cadet can cause your lawn mower to smoke. Most lawn mower owners understand the need to keep their engine oil from getting too low, but they don’t often know having too much oil in the crankcase can also cause engine damage.

The engine oil level must be at the level recommended by the manufacturer.

• Low Oil Level
  Your mower can become low on oil if you develop an oil leak or a more significant problem with your engine. When there isn’t enough lubrication due to a low engine oil level, the parts in the engine are exposed to extreme heat conditions because of the increased friction. These parts can begin to melt and fail.

  When you experience this problem, you can try to add additional oil to correct your oil level and see if your mower will run. Often, when the engine is extremely hot because of poor lubrication, there is extensive engine damage that cannot be resolved by adding more oil. Bring your mower to a small engine mechanic to determine the impact of the damage.

• High Oil Level
  Having too much oil can cause too much crankcase pressure. This increase in pressure can cause oil to move into the cylinder and air intake. The oil that is in the cylinder creates a smoke once it begins to burn off when the engine is running at full speed.

  You need to drain some oil out of the engine to resolve this problem.

Read more about the damage too much oil can cause to your Cub Cadet along with ways to drain a little oil out of the crankcase in “This is What Happens If You Put Too Much Oil in a Lawn Mower”.

3. Cub Cadet Piston Ring Problem

Now you are getting into the more difficult troubleshooting areas to find the reason for your Cub Cadet Smoking. You need to check for oil on the spark plug. Oil on the spark plug is a sign of a bigger internal engine problem.

Remove the spark plug using a socket. You may need a 3/4″ or 5/8″ socket to remove the plug. Remove the plug and check for excessive oil on the spark plug.

This can indicate you have a piston ring problem and a score on the cylinder wall. Oil can enter the compression changer when the cylinder wall is scored. When this oil burns, it creates smoke.

I recommend taking your engine to your local small engine repair shop if you are not mechanical. You will need to take the engine apart to find and fix the engine problem.

Many times, once your engine has experienced this problem, you will have to replace the engine. Depending on the mower, you may be better off purchasing a new mower.

4. Cub Cadet Valve Train Problem

Sometimes having a valve train problem is not that bad of a problem to have. The only way to detect this is by removing the cylinder head or performing a leak-down test. This should be completed by a small engine mechanic.

The cause of a valve train problem is the result of the valve getting burned by being overheated. The edges of the valve begin to fall apart due to the heat. This is what is often referred to as a burnt valve.

You can also see a burnt valve or timing problem if the muffler is glowing red from heat while the engine is running. In this case, you will need to replace the valve and grind the seat. The seat is where the valve makes contact with the engine block to complete the combustion chamber.

Both the valve and the seat will have to be cut at certain angles in order to make the valve seat correctly.

5. Bad Engine Gasket in Your Cub Cadet

A bad engine gasket may leak oil onto the muffler and make the engine smoke as it burns. You will need to find the bad gasket and replace it. This may sound easier than it actually is. It becomes increasingly more difficult depending on the location of the bad gasket.

Difference Between Blue and Black Smoke in Your Cub Cadet Lawn Mower Engine

The color of the smoke can often give you a clue as to what kind of engine problem you have.

Although it is best to go through the list above to narrow down the area that is causing your problems, the color of the smoke can also lead you to the place to start looking for your Cub Cadet smoking problem.

• Black Smoke – This color usually is due to the engine running too 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 it. If this isn’t the issue check for another air flow restriction.
• 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.

It is important to continue to check your engine oil level and air filter before each mowing use to avoid large expensive repairs. For a checklist to perform before each mowing I check out this article.

Complete Regular Engine Oil Changes

It may seem like a lot of work to change your engine oil, but changing your oil is necessary. To keep your lawn mower running and not shorten the life of the mower’s engine, you must change the engine oil regularly.

Read more about the damaging effects of skipping your oil change, “Engine Damage is Likely if You Skip Mower Oil Changes”.

Related Items

Routine maintenance is important to ensuring your Cub Cadet lawn mower remains in good operating condition. Additionally, you need to inspect your mower blades to make sure you are achieving the best cut possible. Read more about mower blades in “Change & Sharpen Your Cub Cadet Mower Blades“.