Why Is Oil Coming Out Of My Lawn Mower Exhaust ? Guides 2021

why is oil coming out of my lawn mower exhaust

You are working in the yard with your lawn mower, and all of a sudden, you notice that it’s leaking oil from the exhaust. If you did not notice this for a longer time, it might have leaked oil all over the yard. Whatever, this is something we don’t except.

The issue can take place due to various technical faults. Your lawn mower’s engine is pretty similar to car engines; the difference is, a lawn mower engine work on a smaller scale.

When you search ‘why is oil leaking from my lawn mower exhaust,’ Google probably directs you to some forums. And finding solutions from forums feel tiring. But this article will make things easy and address the issue along with the solution.

why is oil coming out of my lawn mower exhaust ?

When you start the engine of a lawn mower, initially, four components heat up; pistons, cylinders, exhaust pipe, and exhaust manifold. Oxygen and fuel go into the pistons through valves and force the gas to come out through the exhaust pipe. Oil lubricates the parts around the engine.

The problem appears when any parts within the cycle are damaged or worn, or any activity is out of time. This is when the exhaust leaks liquid or oil.

Oil can leak due to several reasons as follows –

1. Clogged Air Filter

Sometimes it’s the unburned fuel that comes out of the muffler. It occurs because of the plugged air filter that doesn’t let air going into the piston. When the air cannot properly make the way to the pistons, the fuel remains unburned.

Besides, the fuel fails to burn when the carburetor isn’t adjusted, or the float gets stuck inside it. All these incidents cause unburned fuel to eject through the muffler. However, if the liquid that comes out of the exhaust system smells like gas, it’s most likely flooding issue.

2. Damaged Piston Ring

Oil leaks from the exhaust system when the piston ring is damaged or worn. The oil is pushed out from the piston without burning. You might notice slick oil coming from the muffler.

Also, turning the engine, on its side, is also responsible for this leakage. In this condition, the oil burns to some extent when the engine runs.

3. Worn Valves

Worn valves don’t allow the cylinders to seal appropriately; thus, they cause oil leakage into the cylinders. Sometimes, the oil also leaks from the exhaust system of a lawn mower.

4. Coolant

Lawn tractors with a four-stroke engine have the tendency of developing cracks in parts of the cooling system as well as the engine block. The cracks allow coolant to leak from the fuel system and exhaust. Coolant also leaks from the exhaust system due to damaged gaskets.

If you notice green or yellow liquid drips from the muffler, consider replacing head gaskets. However, it might also indicate some issues with the engine as well.

5. Overfilled Crankcase

Most lawn mower crankcases can hold less than one full quart of oil, as the cases in such machines are pretty small. When the case is overfilled, it pushes the oil to move. In most cases, the excess oil goes into the cylinder; it also moves into the carburetor as well.

Oil in the carburetor later goes to the air filter and leaks from the exhaust system. To prevent such an issue from happening, don’t add excess oil at a time.

6. Oversoak Air Filter

If the foam air filter is oversaturated with oil, there will be some oil around the filter box too. Unfortunately, the oil then goes into the carburetor, and gums needle valves and internal jets of the device.

To get rid of it, you need to squeeze out the excess oil from the foam air filter. If this doesn’t solve the issue, consider cleaning the carburetor as well.

7. Tipped Lawn Mower

Tipping your lawn mower more than 15 degrees while pointing the carburetor downwards, can also contribute to oil leaking from the crankcase as well as a breather tube.

Both the carburetor and breather tube are connected to each other, and the carburetor is connected to the air filter. So, if the oil goes into the breather tube, it will eventually make its way to the air filter through the carburetor.

You might unknowingly tip the machine while sharpening or changing the blade, or cleaning deck’s bottom part. The mower may tip when you mow grass across a hillside, which allows the oil to flow to the carburetor. To solve the issue, simply tip the mower so that the carburetor stays on the high side.

8. Blown Head Gaskets

Head gaskets are the parts that block the heads of the engine. This part of the exhaust system is responsible for sealing liquid passages between the block and heads. When there is something wrong with the gaskets, guess what, fluids go to the exhaust system, and escapes through the seal.

9. Cracked Engine Block

All internal parts of your lawn mower engine stay within the engine block. It’s also responsible for flowing the fluids to various components. If there is a crack in that block, it will make fluids to escape, which will end up leaking from the exhaust system.

You might also experience rough running, overheating, poor performance, engine noise from the mower.

What to Do Now?

Oil Coming Out Lawn Mower Exhaust

Some damage such as cracks in the engine, worn valves, and damaged pistons will leave you with no option but replacing or repairing the parts. However, there are some issues that you can fix yourself.

Track the Oil

Oil lubricates many internal parts and makes them operate smoothly. When there is too much oil on a particular hot surface, it causes issues with the exhaust. The trick is, don’t add too much oil or overfill the oil tank.

Poor Operating and Maintenance Skill

When people turn the mower to clean, they turn the carburetor to the other side. Make sure the carburetor is upwards when you turn the side. Don’t push the slope more than 15 degrees to prevent potential damage and oil distribution.

Periodically check the air filter and fuel filter. Consider spraying carburetor cleaner to degrease the chamber to make sure leaked oil cannot attract dirt to cause further issues.

Other Issues

Older machines face problems such as worn or cracked cylinder, leaked crankcase, clogged breather, worn O-ring that contribute to oil leakage. Run regular maintenance to check whether the worn parts and seals require replacement or not. It will prolong your older mower’s life to some extent.

Final Words

Lawn mowers are the most abusive equipment in every house. People hardly care about the maintenance part of the machine.

If you are concerned with ‘why is oil coming out of my lawn mower exhaust,’ you must take care of the maintenance part of the machine.

Resources & References

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Hi, I’m Adam Vachon, an avid learner and working in the product marketing niche for the last few years. The problem I faced when marketing products for manufacturers made me interested in starting GearsLoft.

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