What Does It Mean When Blue Smoke Is Coming Out Of Your Lawn Mower?

When there's smoke coming out of a machine, you can almost always expect something bad to happen. So if your lawn mower starts producing blue smoke, it's only normal to be concerned. Blue, however, is arguably the least alarming color to spot when your lawn mower is smoking. In most cases, blue smoke means oil has reached areas of the engine where it shouldn't be, such as the combustion chamber or air filter.

This can occur for a number of reasons. Maybe you overfilled the crankcase during an oil change, used the wrong oil grade, or tipped the mower on its side a little too far while you were cleaning the deck or changing the blade. Even operating the machine on a steep incline can displace the oil; that's why the Occupational Safety and Health Administration (OSHA) warns against operating small engines at an angle greater than 15 degrees. Once oil strays into a hot engine component, it tends to burn off as a bluish-white smoke.

In these situations, the smoke often appears temporarily and clears once the excess oil burns away. Depending on the amount of oil involved, this might take about 15 minutes. However, if the blue smoke is unrelenting and you begin to notice other issues, like your mower backfiring, it might be a symptom of a clogged or broken part. But not to worry — there are a few simple checks that can help narrow down the problem.

One of the easiest ways to confirm whether this is simply a case of burning oil is to check the dipstick. Before inspecting the mower, turn off the engine, allow it to cool, and disconnect the spark plug. If the oil level is above the full mark, you'll need to drain the excess. Depending on your mower, you can drain oil through the drain plug into a pan, draw it out through the dipstick tube with an oil extractor, or drain it through the fill tube. Similarly, if you used the wrong oil grade, drain it out and refill the mower with the type of oil recommended in the owner's manual. Be careful not to overfill it.

Another thing you need to be careful about is tipping the mower on its side. If you need to tilt it, do so in such a way that the spark plug points upward or the muffler points downward. This helps reduce the chance of oil leaking out of the crankcase. If you've tipped the mower already, set it upright and check if oil has seeped into the air filter. If it's soaked and dirty, clean or replace it as instructed in the manual.

After making these changes, the mower should be running just fine. But if the smoke continues, and your lawn mower is now struggling to start, or just not working at the normal speed, the problem may be a blocked breather tube, broken valve, or worn piston rings. At that point, it's usually safest to have the mower inspected professionally, especially if it's still under warranty.