Why Is My Lawn Mower Smoking? Causes by Smoke Color

Seeing smoke pour out of your lawn mower is alarming, but it doesn't always mean disaster. The color of the smoke tells you what's going on.

White Smoke — White smoke on startup is usually harmless, especially on cold mornings. It's just moisture burning off. However, persistent white smoke can indicate a head gasket leak, which allows coolant (on liquid-cooled engines) or oil to enter the combustion chamber. On air-cooled small engines, white smoke often means oil is getting past the piston rings or valve seals.

Black Smoke — Black smoke means the engine is running rich — too much fuel relative to air. Common causes include a clogged or dirty air filter (the easiest fix — just replace it), a stuck or misadjusted carburetor choke, carburetor flooding due to a stuck float or worn needle valve, or the wrong fuel-to-air mixture setting.

Blue or Gray Smoke — Blue smoke means the engine is burning oil. Causes include the mower being tipped at the wrong angle (oil flows into the cylinder — usually a one-time event), an overfilled crankcase (too much oil), worn piston rings (allowing oil past the piston), worn valve seals or guides, or a blown head gasket.

Occasional puff of blue smoke on startup? Not a big deal — especially on older engines with some wear. Constant blue smoke during operation? That's a sign of internal engine wear that will get worse over time.

What should you do? Start with the simple stuff: check the oil level (not over or under filled), replace the air filter, and make sure the choke is operating correctly. If smoke persists after addressing these basics, bring it in for a diagnosis. Some causes are simple fixes; others may indicate it's time to discuss repair versus replacement.