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.

lawn mower smokingFour candles/Shutterstock

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

What Causes Lawn Mower Smoke (and What to Do About It)

In the majority of cases, a lawn mower engine suddenly bellows out blue or white smoke because oil has spilled onto the engine. The spillage can happen if you added or changed oil and slopped some or overfilled. Or, a spill can happen if you turn the mower on its side or upside down for maintenance or even if you’re simply mowing on a steep slope. The lubrication systems in most mowers are not well sealed and usually have an overflow oil reservoir that has a relief outlet from which excess oil can leak. So, if the problem is simply that oil has found its way onto the engine, the solution is simply to allow the mower to run until the oil burns off harmlessly.

Here’s what to do if your lawn mower won’t start.

If the smoke is black or if 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 should be to check the air filter, after the mower cools down. If it’s clogged, that means 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, which is a very easy task.

If your smoke problems persist, chances are you have a problem with oil seals in the engine lubrication system or around the pistons, or you may even have a cracked crank case. Repairing these problems is a job for a small engine pro, unless you have a good amount of experience working on engines. There is also a chance that the smoke is the result of a carburetor that simply needs cleaning or adjusting. If you are up for it, most owners’ manuals include instructions on how to adjust your carburetor.

Give your lawn mower a quick and easy tune-up today.

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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.