Why is my lawnmower smoking? Four common problems and simple fixes

There are a few things no gardener ever wants to see, and near the top of that list is a smoking lawn mower. Lawnmower smoke is acrid and worst of all, puts a stop to your mowing schedule.

Even the best lawnmowers can be taken out of action by mower smoke, but thankfully it's almost always easy to fix.

I spoke to one of our in-house gardening experts about the four reasons why a mower might produce smoke, as well as the four easy fixes that should get your mower running again.

1. Dirty air filter

The most common cause of a lawn mower smoking is a clogged air filter. A dirty air filter limits airflow, which means too much fuel is getting to the engine and this makes smoke. You can usually tell if this is the problem by the color - black smoke speaks to an incorrect fuel mixture, and this is almost always caused by a dirty air filter.

It's easy to forget to maintain your air filter, but thankfully it's just as easy to fix.

Gardening expert and H&G content editor Drew Swainston told me 'All you need to do is remove the filter cover, remove the filter, and wash it in soapy water. Leave the filter to dry for a few hours and then replace it in the lawn mower. You should find that your mower is running again.'

Drew Swainston

Drew qualified as a journalist and wrote for many websites and publications, before studying for a horticulture qualification. He worked as a professional gardener for several years, specializing in kitchen gardening. He's now bringing his expertise and passion to Homes & Gardens as a member of our team. 

2. Too much oil

If there's a lot of blue or white smoke coming from your lawn mower, it probably means that there's too much oil in the engine. There are two causes for this issue. The first is that you may have tipped your lawn mower. If you tip a gas mower over or mow on a steep slope, engine oil can spill onto the engine and flood it.

When the engine runs, this oil burns, creating smoke. The second reason is that you could have added too much engine oil. If your oil reservoir is overfilled, oil may have spilled onto the engine.

Thankfully, this also has a relatively easy fix. Just run the mower in place for a few minutes to burn off the excess. After a while, the smoke should stop.

3. Old fuel

Gas evaporates over time, so it doesn't keep. Just as with a dirty air filter, old gas can create a poor ratio of fuel to air in your engine. If you've filled up your mower from an old jerry can you have lying around, you may find your mower starts making smoke.

This is another simple fix, but a little bit of a hassle. If your mower is full of old fuel, you must remove it with a cheap siphon like this from Amazon. It's relatively easy but more involved than troubleshooting the other methods.

You can also dilute your old gas with new gas by adding a 3 to 1 ratio of new gas to old gas. However, it's easy to get this wrong, in which case you'll have the same issue as before.

4. Wrong oil grades

Finally, the issue could be that you've added the wrong grade to your mower. Most gas mowers take SAE 30W oil, but not every mower does, so it's best to check the manual. You may also have grabbed the wrong bottle off the shelf by accident.

The best fix here is to drain the oil. I recommend using an extractor pump like this from Amazon; you could drain the oil by tipping the mower on its side but that could repeat the flooding issue outlined above. Once it's drained, add the correct oil grade.

Lawn mower FAQs

Do electric lawnmowers smoke?

It's much rarer than in gas mowers, but electric lawn mowers can create smoke. This usually happens if the engine overheats from dirt, or if the blades or caught up with debris. In this case, turn the mower off and service the engine - the problem should resolve itself once the engine is clean.

For more help with mowers, take a look at our head-to-head comparisons of robot mower vs push mower and riding mower vs push mower.