Why Is My Lawn Mower Blowing White Smoke?

Getting a big cloud of white smoke can be scary. Most people don’t expect it to happen — but why is it even happening?

Why is your lawn mower blowing white smoke? The truth is, it could be one of these reasons:

  • An air leak in your crankcase
  • An overfilled crankcase
  • A broken or not working breather in your crankcase
  • Poor grades of oil
  • If you tilted the engine for more than 15 degrees (even if just for storage)
  • If your cylinder is worn out
  • Head gasket broke

Of course, just knowing what caused your lawnmower to blow white smoke is not enough — you also have to know how to fix it. So, if you want to learn more about these issues (as well as 

some other problems that may be the cause of white smoke), as well as the solutions, read on. 

Common Reasons a Lawn Mower Is Blowing White Smoke

As mentioned, there are some common reasons why your lawn mower may be blowing white smoke. It happens often — much more often than you’d think — and most of these problems are easy to troubleshoot, but more on that later. 

For now, let’s just take a look at all of the possible reasons why your lawn mower may be blowing white smoke. Some of them you’ve already seen at the beginning of this article. Here they are: 

  • Tilted engine, as the most common reason for white smoke blowing out of your lawnmower (no lawnmower should be tilted at an angle bigger than 15 degrees).
  • Oil issues such as overflowing oil or wrong type of the oil are the second most common cause, and it’s often very easy to fix.
  • Leaks are another common issue, and they could cause even more problems if you leave them be.
  • Broken parts such as the head gasket, cylinders, etc. need to be checked for once in a while to prevent these issues.

Other than these causes, there are some less common ones, but it’s good to be aware of them, just in case you are one of the people it happens to. Here they are:

  • Blocking of the breather 
  • Putting more oil than the dipstick shows
  • Damaged piston rings

Fortunately, all of these are easy enough to repair. There’s no room for panic. First, you need to shut your machine off and let it cool down. Then, you can move on to some solutions. 

How to Fix the Most Common Causes of White Smoke in Lawn Mowers

While white smoke looks scary and like a serious issue, it’s actually not. You can fix it in no time if you just follow some simple steps. Naturally, you may not know immediately what caused the smoke, but it doesn’t hurt to test some of these solutions out until you get it right. 

Cause #1: Lawn Mower Tipped Over

Starting with the most basic cause of white smoke in lawn mowers, this one is also the easiest to fix. You’ll also know if this is the cause right away. Has your lawn mower been tipped at an angle greater than 15 degrees? Maybe you stored it that way, or you accidentally moved it like that. 

Most people end up with this issue because of cleaning under the deck or even because they are emptying the chute. When they do this, the oil moves from the crankcase to the cylinder, and once you start mowing again, your lawnmower starts to smoke. 

In some cases, the oil will leak too. 

The best solution for this is to put the lawnmower upright, check the oil in the crankcase (add more if necessary), and then let the engine run until the smoke dissipates. It’s a simple solution, although it may not be comfortable for your neighbors because of all the smoke. 

But if you have a tractor mower, this will usually not be the case, so you have to look for other causes. 

Cause #2: Oil Issues 

In general, your lawnmower will take a little over a pound (near 0.5 l) of oil. This is a really small amount, so it would be no wonder if you overfilled the crankcase once in a while. It’s common. To prevent it, just check the level and the amount carefully before moving on to mowing. 

Often, people think that a little oil can’t hurt anyone, especially not the lawnmower, but the fact is that it could be very bad for their engine. Most engines work on a system of splash lubrication, and if the oil level is higher than the paddles, it won’t work well. 

In this case, the engine is blowing white smoke because it’s trying to burn all of that oil. You can fix it quickly by draining the oil and then let the engine run until the smoke is no longer present. It’s a quick and simple solution, just like with the first cause of white smoke. 

While extracting the excess oil could be bothersome, especially on some models, you should do your best because it will make the process quicker. 

If the oil smells like gas, you shouldn’t run the engine, though. This will mean that your carburetor seal is broken. In this case, you want to make the fix to the carburetor and then change the oil before using the machine again. 

If you try to run the engine without adding proper oil and fixing the problem, you could damage the engine because the oil will be too thin (because of the gas). 

Another thing that could happen is that the oil has found the way to the carburetor, and then the gas can’t get to the jet. If you run the engine a few times, you will be able to spend that oil, and the smoke will go away. If it seems like it won’t work, you should clean your carburetor.  

For one, you’ll have to turn your engine over and then spill the oil from it. Then, you can replace the plug and try again. There are more detailed cleaning measures for the carburetor, but try them after you try this first as it’s simple, and it might just solve your issue. 

You could also put oil in the gas tank by accident, which is a common mistake. To fix it, just drain the oil and put in the gas. Run the engine for a while afterward, so the remaining oil clears out, and the smoke goes away. Again, you could clean the entire carburetor. 

Cause #3: Head Gasket Issues

If your head gasket breaks, you’ll probably see a lot of smoke. It’s less common too, but it’s still possible — harder to fix, too. 

A head gasket is a part lodged in between the cylinder head in an engine and the cylinder block, and it serves the purpose of sealing the area where the combustion happens. Some common symptoms — other than white smoke — of this problem are oil leaks, more pressure in the crankcase, a strange noise, etc. 

To fix it, you have to replace it. 

Final Thoughts

White smoke tends to be concerning, but it’s usually an easy fix. Far more dangerous for your lawnmower is blue or black smoke. With white smoke, it’s just a matter of fixing a simple issue and letting the engine run until the smoke is no longer there. 

Keep in mind that new lawnmowers tend to blow white smoke for a while until they get started and adapt to everything. So, don’t get alarmed if you see this on your first mowing round with your new mower. 

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