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Lawnmower blowing white smoke and leaking oil, why? These are the potential causes

A lawnmower is a convenient machine if you want to keep your lawn in good condition. They are sturdy machines that last for many years. But if the mower is getting older, you can notice that the efficiency is decreasing. It can use more fuel and oil, and there is more smoke coming from the engine. Or the engine is running a little erratic. If you see such issues and would like to fix them, you need to diagnose the reason. There can be reasons like bad gas, a crappy spark plug, or even a broken carburetor leading to these issues. But when you also see oil inside the hood or cover or at the bottom of the engine, there can be a different reason for this.

Lawnmower blowing white smoke and leaking oil, why? These are the potential causes:

  • Blown head gasket
  • Excessive oil usage
  • Engine Oil rings
  • The Lawnmower was Tilted or used at an angle
  • Crankcase leaks

Some smoke from a lawnmower is not uncommon, particularly if it is older. Generally, smoke from any engine is characterized by color. Smoke from lawnmowers may be white, blue, or black. In this blog, we look at white smoke. When an engine leaks oil and shows white smoke, there is a single problem causing this. In some instances, these problems can be fixed easily. Others need a complex, time-consuming fix.

Engine working, lubrication, and cooling

Before we start with the causes of the smoke and oil leakage, it helps to understand how lawnmower engines work. This makes the diagnosis easier.

How does the engine work:

The engine on a gas lawnmower combusts the fuel and air mixture to convert energy from the gas into the flywheel’s rotary motion that drives the blade. This process can be broken down into four parts.

  1. Intake of air and fuel: Air and fuel are mixed in a precise amount. If this ratio is disturbed, the quality of performance is heavily affected. Intake occurs through a valve that is controlled by pushrods and a cam mechanism. The carburetor and related filters govern the air to fuel ratio and rate of the mix.
  2. Compression of the fuel-air mix: The piston moves up inside the cylinder compressing the air-fuel mixture. The reduction enables the power when fuel is burned.
  3. Gas combustion: When the piston is about to reach the topmost position, the energy starts to burn. It happens either by a spark or due to enough rise in pressure. This blast pushes the piston down, transferring power into the flywheel.
  4. Removal of the remnants: When the exhaust valve opens, the remnants are pushed out to muffler by the already caused movement’s inertial effect.


The oil is used for engine lubrication. Oil is added and pumped utilizing the orifices integrated into the engine. To ensure that the oil does not penetrate the cylinder, O-rings are used around the piston. The existence of O-rings causes the oil film to be sealed. Likewise, the gasket also acts as a seal.

Along-with the Oil ring, another ring is also present, wrapping itself around the piston. This ring also plays a very important role. If any of the rings present on the engine’s piston are weak, engine performance will fall drastically. Due to reduced engine activity, the lawnmower’s cutting ability decreases. The other ring, as mentioned, is the compression ring. This ring aims to control the burning pressure inside the chamber and bring it to useful work. When you buy a replacement, ensure that you replace both the Oil rings and compression rings. They are often sold together. 


Lawnmower engines can be air-cooled or use a coolant. Air-cooled has a fin for an enhanced surface area that enables for a fast transfer of heat. Around the same time, the coolant is injected into the jackets around the engine block.

Involved components

Knowing all the active components will allow you to understand the cause and correct any smoke from the lawnmower. Smoke is induced by a problem with the functionality of one of them. And they can be rectified by managing them.

  • Carburetor
  • Head Gasket
  • Air filter
  • Oil filter
  • Breather Tube
  • Fuel filter
  • Oil rings

There are three different types of smoke depending on color: Black, white and blue. There are various reasons for them to occur. Black smoke is usually due to fuel quality or quantity-related issues. Blue and white are often correlated and caused by lubrication oil or coolant problems. Here only white smoke together with an oil spill will be discussed.

Causes for white smoke from the lawnmower and oil leaks

Several causes can result in both white smoke and oil leaks. White smoke is mostly caused when the oil burns inside the cylinder. This is why in most cases, the reasons are the same for both problems. The list of causes will help you diagnose and fix the problem.

● Lawnmower Blown head gasket:

Suppose the head gasket of the engine is lousy, or it is partly or entirely blown. Oil and coolant seep into the combustion chamber, causing white smoke. Some oil will get blown out as well. Marking will be visible inside the hood or cover. A timely repair is necessary to avoid any future damage to the engine.


  • Check for and scuffs or marking or blows around the head
  • Disassemble the engine head
  • Look for carbon deposits of valves and piston
  • If diagnosed as blown, replace the gasket. If not, reassemble all the components


  • Open the engine compartment and examine all components
  • Clean the surfaces
  • Clean the carbon deposits
  • Check the condition of the gasket
  • If completely blown, replace it
  • If partially damaged, use gasket-sealant paste around. But replacing it is always the better option.
  • There are also products that can temporarily fix head gasket issues without opening the engine. If you have limited time, this can be a temporary fix.

● Excessive oil usage:

Overfilling the lubricant oil in the lawnmower can produce white smoke. The chance of spilling some excess oil is also great.


If your engine is blowing smoke, check the dipstick’s oil level, and if the oil level is too high, remove some until it reached the correct right level.


  • The dipstick is located on the reservoir. Clean the dipstick with a piece of cloth and remove the cap from the reservoir
  • Dip the stick for a moment and take it out again
  • Check the level corresponding to marks
  • If the level of oil is too high, remove some of it by draining it through the plug present below the oil pump. Or use an oil hand pump to remove some from the reservoir

● Lawnmower Engine Oil rings:

Oil rings refrain the oil between the piston and cylinder to seep into the combustion chamber. If oil rings wear out, the oil will get into the chamber and burn with fuel. This problem will cause smoke. If not treated, the issue will get bigger and result in other problems.


Oil rings are an internal engine component. The diagnosis is not easy without opening the engine and checking them. These rings have a specified age from the manufacturer and should be changed accordingly.


  • It is customary to check the oil rings health during an engine check-up
  • Replacing the piston rings is the only option
  • Do not try a Self-repair if your expertise level is lower. Ask a professional for help.
  • Ensure you use a proper replacement with the same size and shape. Check the instruction manual for details.

● The Lawnmower was Tilted or used at an angle: 

If the lawnmower is operated at very steep slopes, it can cause oil seepage into the engine block and cause smoke. The problem can also occur after you have done some maintenance on your lawnmower and tilted it.


  • As soon as you use the lawnmower at normal angles, it should solve itself. In general, try using less steep paths.

● Breather tube

Breather tube is commonly regarded to be a member of the carburetor but is often ignored. If there is a blockage in the hose, it will cause the lawnmower to burn.


Clean the breather tube with some carburetor cleaner.

● Lawnmower Crankcase leaks:

Crankcase leaks can also cause white or blue smoke. If your engine is blowing white or blue smoke, check the crankcase for any leaks.

General warning

The mentioned causes all will blow white smoke accompanying with oil leaks. Oil leaks and smoke are hazardous to the environment. Spilled oil will cause permanent filthy marks on the garage floor or where ever the lawnmower is parked. Proper care and maintenance will make the chance for this kind of problems smaller.

Related Questions

1. Is it ok for the 2-stroke engine to smoke?

No, it’s not ok for any engine to blow smoke. While a two-stroke engine burns oil, it should not result in any smoke. If the lawnmower is not correctly maintained, bluish-white smoke can be generated. In that case, further diagnosis is needed.

2. Can the wrong grade of lube oil cause smoke?

Yes, in some instances, especially in 2-stroke engines. Always use the oil grade that the company recomments.

3. What causes a brand-new mower to blow smoke?

Brand-new engines can have some leftover residual oil from the production process within the cylinder. After a few uses, the smoke should stop. If the smoke remains, you should return it to the dealer and let it check there. Or replace it with a new one.

4. Is an oil spill/ leak possible without white smoke?

Yes. Oil can spill without smoke. If the oil pump is damaged or broken, some oil leakage can occur. But in this case, there will be no smoke visible.

Final Remarks

If your lawnmower is blowing white smoke and leaking oil, there can be various reasons for this. Smoke can trigger significant concern and anxiety. Some of the reasons are easy to fix, But some of them, like a blown head gasket, are not. This blog post will help to diagnose and fix several of the potential causes. If you are unsure about the cause or have doubts about how to fix it, ask a professional for help.