Why is My Lawn Mower Smoking?

Updated: May 19, 2023

Leaking oil from the exhaust is the usual cause of blue, white or black smoke from a lawn mower. Learn to assess and fix a sputtering, smoking lawn mower.

Gas-powered lawn mowers can be full of surprises. Perhaps the most startling one happens when you pull the mower cord and the engine sputters into action, only to be followed by clouds of smoke from the motor and under the mower deck. What’s going on and what should you do about it?

Why is My Lawn Mower Smoking?

There are several reasons your lawn mower could be bellowing out smoke. While it looks kind of intimidating, like something bad is about to happen, in most cases, it’s nothing to be worried about, and it’s not usually hard to fix.

Oil spilled onto the engine: If you changed your lawn mower’s oil recently or added more to the oil reservoir, some may have spilled out onto the engine. Mowing on a steep slope in the yard, or turning it over to adjust the blade, could also cause some oil  onto the engine. When that happens, the oil will burn off, causing blue or white smoke. It’s best just to let it burn off, so when you start up again, the oil will be gone.

Overfilled oil reservoir: Too much oil in the reservoir can also cause a lawn mower to smoke. The lubrication systems in most mowers are not well sealed, and usually there’s an overflow oil reservoir with a relief outlet where excess oil can leak. Check the oil level in your mower, and if there’s too much in there, consult the manual for how to drain some out until it’s back at the proper level.

Mower burning too much gasoline: The carburetor regulates the ratio of gasoline and air in a lawn mower engine. If the carburetor isn’t getting enough air, that means the mix is heavy on gasoline, which can cause black smoke from the exhaust. Often times that’s caused by a dirty air filter, which is preventing enough air from getting to the carburetor.

Different Types and Colors of Smoke

If the smoke is black, there may be an engine problem behind the smoke. In such cases, your first step after the mower cools down should be to check the air filter.  If it’s clogged, the combustion chamber may not be getting enough oxygen, resulting in a too-rich fuel mixture that will cause the engine to run poorly and even spew smoke. The solution is to change the air filter, a relatively easy task.

Blue and white smoke is the result of oil on the engine. If there’s too much oil in your oil reservoir, you may want to drain some of it out. If it’s just some oil spilled onto the engine, all you have to do is let it burn off.

When to Take a Smoking Lawn Mower to the Repair Shop

If your smoke problems persist, chances are the oil seals in the engine lubrication system or around the pistons are the issue, or you may even have a cracked crankcase. These are repair jobs for a small engine pro, unless you’ve got experience working on engines.

There is also a chance the smoke is simply the result of a carburetor that needs cleaning or adjusting. If you’re up for it, most owners’ manuals include instructions on how to adjust and clean the carburetor.

Remember, it’s important to tune up your lawn mower at the start of the season, which will help make sure it’s running properly and prevent potential problems like a cloud of smoke following you around the yard.

Troubleshooting and Fixing the Mower

  • Check and replace the air filter.
  • Check oil level, grade and type. Change the lawn mower oil if necessary.
  • If oil has found its way onto the engine, let the mower run until the oil burns off harmlessly.
  • Checking the angle at which you’re mowing. Angles greater than 15 degrees can cause your lawn mower to smoke.