Oil Coming Out of Lawn Mower Exhaust? Reasons and Fixes

Oil coming out of lawn mower exhaust vents is definitely a sign that something is wrong with your mower. It could be extreme tilting, an overfilled mower, or carburetor imbalance, among others.

Oil coming out of a lawn mower, especially from the mower exhaust, can lead to damage and accidents that you should avoid, so read this guide for answers! 

Why Is Oil Coming Out of the Lawn Mower’s Exhaust?

There is oil coming out of the lawn mower’s exhaust becauseof extreme tilting, excess oil, a clogged air filter, carburetor imbalance, worn valves, or engine damage. While the solutions don’t require an expert’s touch, finding the reason can be pretty challenging. 

Extreme Tilting of Your Lawn Mower

Gravity is a serious thing when it comes to lawn mowers. When you tilt your mower the wrong way, you can inadvertently cause oil leaking.

The leak comes from the oil in your lawn mower engine where the crankcase is located. The oil then spills into the cylinders, where it gets pushed through your lawn mower’s exhaust valve. If you notice oil coming out of the air filter, then extreme tilting is the reason.

Overfilled Lawn Mower Oil

When you pour too much oil into your lawn mower, this can lead to oil coming out. It can be further compounded when your lawn mower is tilted.

However, an overfilled crankcase can easily cause an oil leak even at the slightest movement. When this happens, it means that the suggested oil level has been exceeded.

The oil then travels through the engine of the lawn mower and out of its exhaust.

The Air-filter is Clogged

In extreme cases, clogged air-filters can cause oil, or even gas, to spill from the exhaust of your lawn mower. When your lawn mower’s air-filter is clogged, its engine will not have enough oxygen input.

Oxygen is important for the engine as it helps in the gas combustion that powers your lawn mower. When you have oil coming out of your lawn mower’s exhaust, your oil and gas will just be a total waste of resources.

Carburetor Imbalance

When the carburetor of the engine of your lawn mower is out of balance, it can present a problem. The fuel and air will not mix as well as when your carburetor is balanced. This results in oil and gas spills from the exhaust of the lawn mower.

The next time you see black liquid coming out of lawn mower exhaust vents, then this could be due to an imbalanced carburetor. What’s more, it may not just be oil but also gas.

Worn Valves

The engine of your lawn mower has two valves. One is for exhaust while the other is for intake. As your lawn mower goes through its usual functions, these valves eventually wear down.

This condition prevents the cylinders from staying sealed. Unsealed cylinders can cause oil to leak through the mower exhaust.

Damaged Piston Ring

Piston rings help distribute air and gasoline so it can be ignited – or combusted – to make the engine move. It is therefore an integral part of the engine. You should check the owner’s manual as each has multiple rings and there may be unique steps to removing them. You will have to remove them individually and inspect it to see in what condition it is in.

Engine Damage

When you see oil coming out of exhaust vents, then it is also possible that your lawn mower has engine damage. There are several reasons that could have caused your engine to become damaged.

Some of the possible reasons for engine damage can be a blown head gasket, a broken piston ring, or worn valves. These parts require skill and knowledge and, unless you have them, it would be better to ask an expert to check them.

As with air-filters, it’s always best to have an extra head gasket or two. A blown head gasket is no laughing matter, and may even cause more engine damage than you previously thought.

Engine parts can be complex, so a damaged piston ring can be detrimental to your lawn mower. Piston rings can wear away pretty quickly so it’s best to store some in case your lawn mower happens to have a damaged piston ring.

This is especially true if your lawn mower is an older make or model. If this is the case, it’s better to have it looked at by an expert.

How Do You Solve Causes of Oil Coming Out of Lawn Mower Exhaust?

To solve each cause of oil coming out of lawn mower exhaust, you can take various actions such as avoiding titling the lawn mower too much.

Other fixes are to avoid overfilling your mower, solve clogged air-filters, correct your carburetor, repair and replace valves and check damaged engine parts.

Keep the Lawn Mower Upright

Even the slightest degree can affect the title of your lawn mower. When possible, ensure that your lawn is at the most level it can be. Another way to prevent extreme tilting is to keep and maintain your lawn mower on an even surface. This means that the surfaces should be as level as possible for your garage floors and garden areas.

When tilted downwards, the oil in your lawn mower can accidentally escape through the carburetor and the air-filter. If your lawn mower tips downward for any reason, immediately check both parts.

If there’s any oil spillage, clean it immediately. Replace dirty air-filters and wipe off any oil or gas leakages. If there are places that are hard to reach, don’t worry too much about it. The oil or gas spots will start to burn off as soon as the engine of your lawn mower starts to run.

Avoid Overfilling Your Lawn Mower

By simply filling the oil to the suggested amount, you can avoid leaking oil coming out from the exhaust of your lawn mower. Before your pour, test the depth of the current oil content by using a dipstick.

Slowly pour in the soil and check regularly if you have reached the appropriate level. Stop adding in engine oil once you are near full content.

Replace Clogged Air-filters

The solution to clogged air-filters is simple: replace them. When buying lawn mowers, it’s always best to buy engine parts and accessories beforehand.

If you don’t have any, then buy one or two extra and keep them at home. This way, whenever you need to replace the air-filter for your lawn mower, you won’t have to go out of your way to drive for just one item you need.

You might want to think about getting a foam air filter. A foam air filter is known to be better than paper ones, although you may need to check with your lawn mower model if this material is allowed and available.

Correct Your Carburetor

If you know how to clean your carburetor, then you can clean the entire thing by removing the parts one by one. However, it can be a bit tricky since there are so many parts.

On the other hand, you can use a spray carburetor cleaner available in home depot centers. Once clean, make sure that the carburetor is balanced aside from being clean.

Repair and Replace Valves

Most of the time, the valves in the engine of your lawn mower can simply have come loose from constant knocking. If this is the case, you can just simply tighten the valves into their places.

If you are unsure where the valves of your lawn mower are located, you can refer to your owner’s manual. If the valves are beyond repair, replace them. This can help you prevent oil from coming out of the exhaust of your lawn mower.

Check and Remove a Damaged Piston Ring

Use the special tool available to remove and replace the rings – a ring expander. However, you can usually use needle nose pliers to get the job done. You should remove the rings – and since you are replacing them it does not matter if they get damaged – and then clean the piston in the area by wiping the grooves and removing any oil. Also check all of them as they can be leaking from multiple pistons.

Check Damaged Engine Parts for Repair or Replacement

If you are quite familiar with engine works, then you can easily repair your damaged lawn mower. At the very least, replacing damaged engine parts of a riding mower should be an interesting project for any intermediate or expert engine mechanic.

If you suspect engine damage to be the cause of lawn mower oil coming out of breather holes of your lawn mower but are not an expert, then call one. It’s always best to call a professional rather than experiment with repairs yourself.

For instance, you may be unsure about how to clean oil out of a lawn mower muffler for fear of causing engine damage. If this is the case, you may be better off asking the experts and professionals. You can even get some maintenance tips about your riding lawn mower from them at the same time. Check out our guide on how long does it take to charge a mower’s battery.