Mower Blowing White Smoke: Possible Causes & Quick Fixes

mower blowing white smoke

White smoke blowing out of your lawnmower is almost unavoidable if you have had your mower for long enough. It is alarming when white smoke bellows out of your mower but can be fixed when you identify the cause.

Your mower can blow white smoke if there is more than 20 ounces of oil in the engine or if the head gasket is damaged. White smoke will emit from your mower if you mow at a 15-degree incline because oil can enter the engine cylinder. Replace your carburetor seal if it is damaged so that gasoline does not mix with oil and create smoke.

There are several quick solutions for avoiding white smoke in your mower, some as simple as filling with 20 oz of oil or less. Other fixes include replacing the head gasket which is a common and simple solution to white smoke.

Let’s dive into some of the causes behind your mower blowing white smoke and what you can do to fix it.

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Too Much Oil In the Engine

It is easy to put too much oil in your mower engine on accident. Just as under-filling your engine with oil is bad for your mower, overfilling it is bad as well.

Too much oil in your mower’s engine causes the excess oil to enter the cylinder. Anytime that oil gets into the engine cylinder and combustion chamber, it is going to burn. That creates white smoke once the engine gets hot enough.

You can also cause damage to the mower by overfilling it with oil. Sometimes, a mower with too much oil in it won’t even start.

How Can I Fix It?

There are several quick fixes to excess oil in the engine causing white smoke, such as:

  • Drain oil from your engine by loosening the cap, tipping it, and letting it run out
  • Check your directions to see the recommended oil capacity (often 20 oz)
  • Make sure the oil level is correct by using a dipstick

If your white smoke is caused by excess oil, the above steps are the best and quickest solutions.

Faulty Head Gasket

Head gaskets sit between the cylinder head and cylinder block, and when they are damaged, can cause white smoke. Check to see if your lawnmower has an overhead valve (OHV) engine, and if so, it may be behind your white smoke emissions.

Essentially, head gaskets keep your engine secure, so when one is damaged or leaking, oil can enter the combustion chamber. When oil gets into the combustion chamber, your mower will typically emit white smoke.

How Can I Fix It?

The only way to get rid of white smoke caused by a faulty head gasket is to replace the head gasket altogether. There are really only two options for replacing your mower’s head gasket:

  • Buying a replacement and installing it yourself (between $8 and $30)
  • Hiring a lawn mower repair service ($100+)

If you are confident enough to replace your head gasket by yourself, it is the cheaper option. Replacing a head gasket on your lawn mower is fairly simple and can be done in a few quick steps.

  1. Identify your engine type (make sure it is an OHV engine)
  2. Carefully remove your mower’s spark plug
  3. Remove the cylinder head by unfastening the bolts
  4. Remove the gasket carefully
  5. Install the new head gasket
  6. Attach spark plug wire to the spark plug itself

If you are uncomfortable doing that yourself, enlist the help of a professional to rid your mower of white smoke.

Mowing at a Steep Incline

One of the main causes of white mower smoke is mowing at a steep incline. Depending on your yard, mowing at an incline may be unavoidable. Unfortunately, when you mow at too steep of an incline, oil can reach the cylinder in the engine.

Your mower’s cylinder gets quite hot while in operation, so when the oil reaches it, it combusts. That in turn produces white smoke.

How Can I Fix It?

There are several ways to resolve your white smoke problem caused by steep mowing, such as:

  • Avoid mowing at 15 degree incline
  • Idle the mower for as long as it takes for all of the oil to burn off
  • Drain the oil

If your lawn is very steep and mowing at inclines is unavoidable, white smoke may be a common issue. If so, consider getting a mower that is intended to handle steep inclines, like some zero turn mowers.

Tipping the Mower on the Wrong Side

Tipping the mower on its side the incorrect way is the same as mowing at a steep incline. It can cause oil to reach the cylinder which will create white smoke. Often times, people will tip their mower the wrong way when changing the blades or maintaining it.

Check the directions to see which side it should be turned on before you maintain your mower next. No two mowers are alike and the side it should be tipped on for maintenance varies from model to model.

Tipping your mower on the wrong side is a common problem to encounter but it is also the easiest to fix. Pay attention to the directions and next time that you maintain it, make sure that you aren’t tipping it over on the wrong side.

Damaged Carburetor Seal

Gas mixing with oil caused by a defective carburetor seal can also cause your mower to emit white smoke. Carburetors work by mixing air with gasoline by way of a hose going out of the fuel tank.

If the carburetor is damaged or defective, the gas won’t just mix with air, it will mix with oil. If you see white smoke and think it may be caused by the carburetor, shut the mower off.

Check the oil using a dipstick, and if it smells like gasoline, that means it is a carburetor problem.

How Can I Fix It?

To rid your oil of gas, you will need to fix or adjust the carburetor by following a few easy steps.

  1. Remove the carburetor, strip it, and clean it
  2. Soak the carburetor in special carburetor cleaner (products like Gold Eagle, Gumout, and Super Tech)
  3. Replace the seal and float needle on carburetor
  4. Replace the carburetor entirely if the above steps do not work
  5. Change the oil

You should be able to get rid of the white smoke by removing, cleaning, and reinstalling your carburetor. If that does not work, you may need to replace the carburetor altogether. Replacing the carburetor on your own only costs up to $60 at the most for parts.

However, the cost of hiring someone to replace your mower’s carburetor adds up quickly. Mower maintenance specialists often come at a $50-$70 hourly rate, not including the $50-$60 for parts.

Fixing the carburetor will keep gas out of the oil and get rid of the white smoke.

Damaged Piston Rings

If your mower is fairly old and blowing white smoke, chances are that the piston rings are damaged. Over time, the piston rings on mowers get worn out and eventually quit working as well as they once did.

Piston rings are responsible for your mower removing oil from the engine and combustion chamber on its own. In many ways, piston rings are your mower’s defense against oil combusting and creating white smoke.

Running a mower with too little oil can cause the piston rings to become damaged and defective. They can also become damaged if you have been using the mower for years without maintaining the part.

If your mower’s air filter is damaged, your mower can’t remove particles that could damage the piston rings.

How Can I Fix It?

Unlike the other causes of your mower blowing white smoke, damaged piston rings are not an easy fix. In fact, many people will opt to replace their lawnmower altogether because of all that fixing piston rings entails.

There are two options for fixing damaged piston rings:

  • Open and rebuild the engine entirely
  • Use thicker oil than you are using

Using thicker oil is only a temporary fix to damaged piston rings. Thick oil helps create a stronger seal in the combustion chamber thus preventing oil from burning.

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Final Thoughts

If your mower is blowing white smoke, inspect it and see if any of the above causes are at the root of the problem. Unless the cause of the white smoke is damaged piston rings, fixing the problem is easy and can be done by yourself.

If you have any doubts about fixing your mower, reach out to a professional and eliminate your white smoke problem.

Nick Durante

Nick Durante is a professional writer with a primary focus on home improvement. When he is not writing about home improvement or taking on projects around the house, he likes to read and create art. He is always looking towards the newest trends in home improvement.

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