I would go as far as to say that every lawn mower owner has seen smoke coming from their mower at least one time. Whether just a bit comes out of the exhaust when you first start it, or your mower blows big clouds of smoke while it’s running, it’s not exactly something that you want to see.
While some causes of a smoking mower are no big deal, sometimes it can be the signal of a pretty serious issue. Most commonly, the smoke your mower emits will appear to be white or slightly bluish. Reasons for why your lawn mower is blowing white or blue smoke can vary depending on what type of mower you have, and recent use or repairs you may have done.
Why is My Lawn Mower Blowing White or Blue Smoke?
If you have a lawn mower blowing white or blue smoke, you can be almost certain that it is due to the engine burning oil. These are reasons why your engine could be burning oil (from the most common to the least):
- The lawn mower was tilted on its side incorrectly, or was used at a very steep angle.
- Too much engine oil was put into the lawn mower.
- There is oil in the lawn mower’s fuel.
- Damaged/malfunctioning parts in the engine such as head gaskets, piston rings, or cylinders.
Let me explain each of these causes in more detail so that you can determine which one(s) might apply to you and your lawn mower.
Tilting Lawn Mower Incorrectly or Steep Angle Use
This is definitely the most common reason for oil making its way to places in your lawn mower where it shouldn’t be. Once the oil has escaped, it makes a huge mess and at least a portion of it will burn off and create that white smoke. If your lawn mower is tilted past 15 degrees the wrong way a number of bad things can happen. I don‘t carry around a protractor when I need to clean my mower, change/sharpen the blades, or tackle hills in my yard, but I do keep an eye out for signs that the mower was tilted too much. Burning oil and white/bluish smoke is an easy one to notice, but if you think this might be the case for you, take a look at your air filter. When oil leaks out because the mower was tipped incorrectly, the air filter will almost always get soiled.
Overfilling the Engine Oil
Engines need oil but they need it in a very specific amount. Lawn mower engines take a small fraction of what a car requires, but the oil plays an equally important role. If you have too much or too little oil, the engine will suffer. Since oil needs to be changed relatively often, it can be easy to slip up and put in the wrong amount of oil. If you saw signs that your lawn mower was low on oil, and have changed or added oil to your mower lately, this is a likely contender for why it’s producing smoke. Luckily, you can usually just check your dipstick to see if this is the problem.
Oil in the Fuel of Your Lawn Mower
This issue is quite specific to the type of engine your lawn mower has. If you have a 2-stroke mower, mixing oil into the fuel is required. But, if you have a 4-stroke mower, the gas and oil are designed to be separated. Still, white or blue smoke from the engine can occur to both types. A 2-stroke mower can produce white/blue smoke if there is too much oil mixed into the fuel. As the engine runs, the extra oil will get burned off with the gas. If you put fuel into a 4-stroke mower that has oil and gas mixed into it, your lawn mower will be billowing bluish or white smoke. This is bad news for 4-stroke mowers and can gum them up and damage their engines.
Read more about the differences between 2 stroke vs 4 stroke lawn mowers.
Engine Parts Gone Bad
Bad engine parts can lead to fuel or oil getting around where it isn’t supposed to be just like the other three causes. The most common engine parts that cause white or blue smoke when they fail are head gaskets, piston rings, and cylinders. If any of these are the case you are looking at a pretty sizable small engine project. Since it’s harder to poke around the engine to determine if bad parts are the problem, a process of elimination works well. If you’ve looked into all the other causes of white/blue smoke and are sure that they aren’t the case for your lawn mower, something must be off in the engine. Most of the symptoms from the other causes can be replicated by the oil leaks from failing engine parts.
How to Fix a Lawn Mower Blowing White or Blue Smoke
Fixing your lawn mower blowing white or blue smoke can require a varying degree of time and abilities. Some of the repairs are super straightforward but some can get pretty complex. I’ll use the same descriptions of the above causes to talk about their fixes.
Tilting Lawn Mower Incorrectly or Steep Angle Use – Solution
In this case, your best bet is to wipe off any visible engine oil and then allow whatever remains in the combustion chamber or inner parts of your engine to burn off as the motor runs. Once the oil has all burned off you shouldn’t see any more white/blue smoke. Also, if you suspect this is the cause of the smoke, make sure you check the air filter as it may be dirty. If it has a bunch of oil on it you should replace the air filter and also consider checking/cleaning your carburetor as oil could have leaked into it as well.
Overfilling the Engine Oil – Solution
If your dipstick says there is too much oil in the crankcase, you’ll need to drain the excess out. This can be really simple or kind of a pain depending on the make of lawn mower you have. In any case, the best way to go about this is to completely drain the oil and then add the recommended amount. Double-check that you have the correct amount of oil in your lawn mower after this process. Some people assume that a little bit of extra oil can’t hurt anything but that’s not exactly true. While underfilling is a bit worse, having too much oil will lead to more smoking and extra strain on the engine.
Oil in the Fuel of Your Lawn Mower – Solution
If you have a 2-stroke lawn mower and you’re certain that there is only a little bit too much oil in your fuel and there isn’t much fuel left, you can probably get away with just burning through the remaining fuel. Because 2-stroke engines are made to burn an oil/gas mix, there are very low odds that you’ll run into trouble. If you have a 4-stroke mower you should treat oil in the fuel with more caution. This means that your best option is draining the fuel completely of the contaminated gas and adding fresh gas. The same goes for a 2-stroke mower with a mostly full tank. After doing this, be sure to check the oil level of your mower and replace any oil that might have leaked out. You might see a bit more white or blue smoke while the residual oil burns off.
Engine Parts Gone Bad – Solution
To get a detailed description of all the ways to fix internal engine parts you’d need a manual. If you don’t have a ton of small engine knowledge and you have looked over the other causes of lawn mowers blowing white or blue smoke, your solution is going to be a small engine mechanic. Getting a diagnosis from a mechanic will open options for a more involved repair project if you’re interested.
Riding Lawn Mower Blowing White or Blue Smoke: Here’s Why
All of the above reasons commonly apply to riding mowers other than tipping the mower over. Obviously, this is a lot harder to do with a riding mower. However, there is one issue that often causes white/blue smoke in riding mowers: carburetor issues. If you notice white or blue smoke pouring out of your riding mower, it is probably because oil and gas have mixed. Here is what to do:
- Drain and replace the engine oil.
- Drain and replace the gas.
- Change the fuel filter out.
- Clean the carburetor.
If your riding mower is still producing smoke after this process, there is likely an issue with an engine part.
Causes of 4 Stroke Lawn Mower Blowing White or Blue Smoke
All of the most common causes listed above apply to 4-stroke lawn mowers. The only important distinction to make is when addressing oil that has mixed with the fuel, and overfilling engine oil. Because you add oil separately from fuel in a 4-stroke mower, the process of diagnosing and fixing issues with burning oil will be different than with 2-stroke mowers.
Causes of 2 Stroke Lawn Mower Blowing White or Blue Smoke
When 2-stroke lawn mowers blow white smoke, all of the same causes listed above still apply but they do so a little differently. This means that issues of fuel mixed with oil and overfilling engine oil come from the same problem with 2-stroke engines: too much engine oil mixed with the gas. Making sure to check that you have a correct ratio with your gas/oil mix is a good way to prevent smoking.
Is White or Blue Smoke from My Lawn Mower Dangerous?
In short, yes. The dangers of white/blue smoke from lawn mowers are health-related: your health and your lawn mower’s health. You don’t need a doctor to tell you not to breathe in smoke resulting from burned oil. And if your lawn mower does have problems that cause oil to burn, it’s a hard-to-miss sign that there is a problem that will get worse. Oil can damage other parts of your mower like the air filter and spark plugs, but it can also damage engine parts that aren’t meant to come into contact with oil. Though some problems that produce bluish or white smoke won’t hurt your mower too badly, make sure you take the time to investigate if you notice your lawn mower smoking. If you have a lawn mower producing black smoke, you’re probably looking at a different set of problems.