oil coming out of lawn mower

Oil Coming Out Of Lawn Mower Exhaust: Why & How To Fix It

Is your lawn mower blowing oil out of the exhaust? If it is then this is probably something that has been concerning you. But don’t worry, you aren’t the first person that this has happened to and you won’t be the last.

But if there is oil coming out of the exhaust on your lawn mower then you will need to figure out what’s causing it in order to fix the problem. This guide provides you with several scenarios that could cause this problem and what you can do to solve it.

One of the most common reasons that you may have oil coming out of the exhaust on the lawn mower is because the oil inside has shifted when the mower has been moved. This often happens if you’ve tilted the mower on its side for maintenance.

But there are other things that could cause this to happen including a damaged piston ring or an overfilled crankcase.

The good news is that, once you figure out what is going on, you should be able to fix it. It’s really working out where the problem is that’s the most difficult thing.

Causes Of Oil Coming Out Of Your Mower’s Exhaust

There are a few different things that can cause oil to leak out of your lawn mower’s exhaust. While this might seem like a worrying problem, you can fix it by following the advice we give in this guide. Take a look through the following points to see if you can identify the root cause of the issue.

Overfilling Your Lawn Mower’s Oil

You can have too much of a good thing and that is very true of the engine oil you put into your lawn mower. If you put too much in then this is a guaranteed path to leaks.

This may look very much the same as when you tilt your lawn mower incorrectly and we will look at that in more detail later on. But what essentially happens is that the oil will move through the engine and come out of the exhaust.

adding oil to lawn mower

Solution

When you add oil to your engine, make sure that you don’t rush the process. Using a funnel can help to slow things down and also make sure that, if you do add too much, you drain away any excess.

Sometimes, you will leak oil as you put it into your mower and this can get into places where it shouldn’t be. If you think this might be the case then just check the oil levels and make sure that the carb and air filter aren’t covered in oil. If they are, you will need to clean or replace them.

Oil Spillage From Tipping Mower

When you perform maintenance on your lawn mower, you may need to tilt it onto its side. This is usually if you’re working on the blade or other components on the underside of the deck. However, if you tilt your lawnmower to more than a 50 degree angle, this can cause oil to leak out of the crankcase and get into the carburetor.

Moreover, this can happen when you are using the lawn mower on a slope and this is when you might notice oil leaking out of the exhaust. You should also keep in mind that, if oil has leaked through to the exhaust this way, your air filter will also likely be affected so you’ll want to check that too.

Solution

When you are mowing on steep hills, be mindful that this could affect the oil flow inside your machine. Where possible, we would suggest steering clear of too steep slopes and stick to flat ground.

When you are performing maintenance on your lawn mower, be sure to always tilt it the right way. You must make sure that you only tilt it to one side. You’ll know which way to tilt it as the carburetor and air filter should be facing upwards. This stops any oil or fuel from leaking into places it shouldn’t go.

If you have tilted it the wrong way then you’re going to need to check and clean the air filter as well as the carburetor. There may be small traces of oil left behind that you can’t get to but these should burn away as you use the lawn mower.

Clogged Air Filter

While some of the other issues listed in the guide are relatively common, a clogged air filter causing oil to come out of the lawn mower exhaust isn’t quite as common. However, it is possible so it’s worth checking to see if this is your issue.

This happens when the air filter becomes very dirty, This dirt prevents air from being able to pass through the filter which stops the combustion process from happening. Even if the process does happen, it’ll be likely that there is too much gas and this can get into the muffler and out through the exhaust. So, while you think you’re seeing oil, what you’re actually seeing is fuel.

Solution

This really only happens when you’ve got a really dirty air filter. Therefore, it goes without saying that keeping it clean will solve a lot of your problems in the future.

However, if you’re already in this situation then the only real solution is to take the air filter out and give it a good clean. In some cases, even this won’t be enough and you’ll just be better off replacing the whole thing.

Carburetor Out Of Balance

The carburetor can sometimes get out of balance and this will affect how the fuel and air mix together. The result of this is that you’ll likely see some oil as well as some gas coming out of the exhaust.

The excess fuel that isn’t burned will drain out of the exhaust and not only is this inconvenient but it’ll also mean that the mower gets through more fuel which is nothing but a waste.

clean or adjust carburetor

Solution

The best way to address this issue is to clean your carburetor and adjust it. Not only will this solve the problem of leaking oil but it’ll also boost the overall performance of your lawn mower.

You can buy spray carburetor cleaner which is very effective but in some cases, there may be so much dirt that you can take the carb apart and give it a detailed clean.

Damaged Engine

Finding out that your engine is damaged can be devastating as this can be an expensive fix. However, you need to face the problem if it is there and this is a reason that oil might be leaking out of the mower’s exhaust.

Things like a damaged piston ring, broken valves or a blown head gasket could be the root of the problem. If you’re not entirely sure what to look for then you might need to take your lawn mower to a professional who will be able to diagnose the problem. For newer mowers, it should be easy to fix but if your mower is getting on a bit, you might find the problem is a little more severe.

Solution

For many mower owners, they have a good deal of knowledge about small engines, especially if they’re previously used other gas powered tools. In this case, it’s perfectly reasonable that you might attempt to fix the problem yourself.

But again, if you aren’t entirely sure, it’s best to leave it to the pros as you might end up doing more harm than good. And if the mower is still under warranty, dodgy attempts at a DIY fix could void it.

Worn Out Valves

Inside the lawn mower cylinders there are a number of valves that are there to seal the cylinder properly. When the valves become worn out, the cylinder won’t fill up but the oil needs somewhere to go and the easiest exit is through the exhaust.

Solution

Fortunately, this is a very simple fix and involves changing the valves out for new ones.

What Happens If I Don’t Fix This Quickly?

Having oil leaking out of your lawn mower’s exhaust is a serious problem and not something you should put off dealing with until later. If you don’t handle the situation quickly, you may experience the following:

  • Things could become worse, especially if there are problems inside the engine. Ignoring these issues might make them worse and when it comes to repairing them, you’ll probably find that things aren’t as simple as they would have been initially. Moreover, if you don’t address the issue then other parts of your lawn mower such as the air filter and spark plugs might become damaged.
  • You could be harming your lawn by not fixing the problem as having oil constantly dripping all over it isn’t good for its health. In the worst cases, you’ll end up killing it.
  • When you start your lawn mower, any oil that is where it shouldn’t be could cause the mower to emit smoke. Usually this will be white or blue and it could be dangerous for you to breathe in, not to mention the damage it’ll do to the environment.
  • Most urgently, not fixing the problem could cause a fire hazard. If there are flammable liquids, like oil, on the lawn or anywhere else, just a single spark could make it ignite.

Can I Prevent Oil From Leaking Into The Engine?

One of the best things you can do to prevent oil from leaking into your lawn mower engine is to make sure you have a good maintenance routine.

Should I See A Professional?

Most of the things we have discussed in this guide can be dealt with at home. However, if you are in any way unsure of how to diagnose or fix the problem, we would recommend taking the mower to a professional.

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Andrew Fisher

Andrew Fisher

Andrew is a dedicated father of three who really takes pride in his lawn and garden. You'll find Andrew behind the scenes of almost everything Edge Your Lawn produces. When he's not helping readers find all the information they need, he's in his backyard working on his lawn and garden landscaping. This year he hopes to build an outdoor deck and sort out his veg patches.