Why is My Lawn Mower Blowing White Smoke? Here’s Why

Lawn mowers can be quite finicky, especially if you’ve never worked with one before. Smoking, sparking, and loud noises are a few of the frustrations that you might have to experience with a mower. Surprisingly enough, white smoke coming out of a lawn mower isn’t always a cause for replacement.

A lawn mower blows white smoke because it has an overfilled oil chamber, it has a leak on the muffler, or there’s a clog somewhere on the air filter. Other possibilities include worn out piston rings, broken gaskets, and crankcase blockages.

Throughout this article, you’ll also learn the following details about lawn mowers that blow white smoke:

• Several causes of why your lawn mower is smoking
• How to prevent or fix a smoking mower
• When you might want to consider a replacement

Different Causes of White Smoke from a Mower

A smoking lawnmower is a cause for great concern. Before you panic, you should know that it’s not very serious, in most cases. There are different reasons as to why a lawnmower would emit white smoke. Some are as follows:

1. Overfilled oil chamber: According to Lawnmower Fixed, overfilling the oil chamber saturates the oil pan gaskets and causes them to fail. Most lawn mower engines operate a splash lubrication system, so when the oil level is above the splash paddles, they don’t work efficiently. Examine the oil chamber to determine if this could be the issue.
2. Leaks on the exhaust muffler or oil chamber: Leaks could occur when, for instance, your mower inclines towards a particular side when moving on an uneven area, causing the engine to smoke. Another cause for leakages would be when you tip over your lawnmower, which would happen when cleaning the deck or unclogging the chute. White smoke comes out due to the combustion of the leaked oil when you fire up the lawnmower.
3. Blocked air filter: This is another cause for a smoking lawn mower. A blocked air filter could trigger the engine to spew out the smoke with an oil-like smell as the engine pulls oil past the piston rings.
4. Piston ring wear: A problem with piston rings could cause white smoke. There are three rings on a typical lawnmower engine piston:

1. The compression ring (uppermost ring)
2. Wiper ring (in the middle)
3. The oil ring

Piston ring-wear or failure happens when the combustion chamber exerts a lot of pressure on the piston rings.

If the combustion pressure of the gas produced inside the chamber is higher than the usual due to detonation and pinging of the fuel from the leaky injector or when the fuel is mixed with dirty air, the ring performance may be affected.

Also, contaminated fuel oil or the wrong grade of cylinder oil is a significant contributor to piston ring wear or ineffectiveness. This causes the piston ring to be unable to seal the combustion gasses.

5. Blocked crankcase breather: If this is clogged, it will cause the crankcase to pressurize, and the by-products of combustion will contaminate the oil resulting in white smoke.

How to Prevent or Treat White Smoke

Most people are startled by a smoking lawnmower, as many tend to think that it’s about to blow up. The following tips will help you prevent or treat a smoking lawnmower:

• Check the oil chamber to ensure that it’s not too full since it’s a common cause for a smoking lawnmower. Drain the excess oil and let the engine idle until it cools, and the smoke clears. Use the Koehler Multi-Use Siphon Fuel Transfer Pump Kit to make it easier on yourself.
• Tighten the lawnmower fuel caps: In case of leaks on the oil chamber or the exhaust muffler, especially when your machine is tilted sideways when dealing with a sloppy area, turn off the mower’s engine and wait until it has cooled down. Examine the oil chamber for leaks if there are any. If there aren’t any leaks, then there’s a possibility that the cap is loose. Tighten the lid and start the mower. If the problem persists, try out the Briggs & Stratton Fuel Tank Cap (ensure that it’s compatible with your mower).
• Repair the carburetor: If the smoke smells have a gas-like smell, it’s likely because you have a failed carburetor seal. It’s advisable not to run the engine since the oil is too thin and offers no protection. Change the oil after making repairs to the carburetor.
• Doing a compression test: Piston ring wear can be confirmed using a compression test. This is a rare condition, but when it happens, it’s too expensive to fix, so you might as well get a brand-new engine (or lawn mower, for that matter).

 When is it Too Late?

The following are some instances when irreparable damage associated with lawnmowers has occurred and might need replacement:

1. A mower that catches on fire. Fuel hazards are one of the leading causes of fires in gas-powered lawnmowers. This happens mostly in summer due to the high temperatures from the blazing sun. While the heat by itself won’t cause the equipment to overheat, using it during this time for a prolonged time may cause it to overheat. The engine catches fire when fuel leaks onto the motor or fuel vapors around a hot muffler.
2. Melted internal parts. As Cut Grass Pro suggestions, melted internal parts are also a result of an overheated lawnmower. Apart from external factors, such as the summer heat, internal factors may cause a lawnmower to overheat. These factors include low engine oil, blocked cooling fins, low coolant, clogged air cleaner, inlet screens or air paths, clogged cutting decks, and mowing thick wet grass. Overheating can damage the mower by melting parts or blowing gaskets, primarily if it’s used for long periods.
3. Locked or jammed blades. Stuck mower blades are quite frustrating. The causes for a stuck blade bolt is usually rust or over-tightening. You might also have a broken or chipped blade. This issue may be fixed using an impact tool, vice leverages, or tool leverage, although this process is time-consuming. It’s especially common on rotary mowers.
4. Constant white smoke. Constant white smoke coming out of your mower is sometimes fixed by replacing a head gasket, which isn’t usually expensive. In the case of worn-out piston rings, it’s often sadly a dead end. This is definitely a call for a rebuild or a new mower altogether. 

When white smoke comes out often, you’ll definitely have a severe issue on your hands. That being said, a few repairs can fix the problem without having to buy another lawn mower.

Final Thoughts

As you can see, white smoke coming out of your lawn mower isn’t the end of the world. There are plenty of fixes that you can try out in order to save your mower from the dumpster. Most of the issues are related to the gas tank or the oil chamber.

Here’s a quick rundown of the post:

• Always try to repair your lawn mower before you replace it.
• Remember to unplug your mower or remove the batteries if it’s electric.
• If you see smoke of any color, stop mowing immediately.
• Remove built-up grass and debris clogs in your lawn mower to prevent white smoke.
• Always tighten loose caps.