Why is My Lawn Mower Smoking?

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 cord and the engine sputters into action, only to be followed by clouds of billowing smoke from the motor and under the mower deck. What’s going on and what should you do about it?

Why is My Mower Smoking?

In most cases, a lawn mower’s engine suddenly bellows out blue or white smoke because the some of the oil spilled onto it. Maybe you added or changed the oil and slopped some, or overfilled. Or maybe you turned the mower on its side or upside down for maintenance. Even mowing on a steep slope can be the source. 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.

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Different Types and Colors of Smoke

If the smoke is black, or you continue to see blue or white smoke after the mower has run for 10 or 15 minutes, 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 replace the air filter, a relatively easy task.

Potential Causes of a Smoking Mower

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 your carburetor.

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.

Mark Johanson
Mark Johanson is an experienced home and garden writer/editor/publisher. He has written several books and hundreds of magazine articles. He has edited and directed more than 400 DIY and gardening books, including the BLACK+DECKER® Home Improvement Library series and two of the best-selling gardening books in North America. He is an experienced DIYer and enthusiastic gardener.