Lawn Mower Blowing White Smoke

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Did you recently discover your lawn mower blowing white smoke? White smoke blowing out of your lawn mower is usually a sign that there is oil somewhere in the mower that it isn’t supposed to be.

In this article, I talk about 5 common reasons your lawn mower blows white smoke, whether it is a 2-stroke or 4-stroke engine, and also share easy-to-follow steps to diagnose and fix these problems.

Why Is My Mower Blowing White Smoke? 

To figure out how to fix your mower smoking problem, you have to first address the cause of the problem.

The reasons your lawn mower blows white smoke may include:

  • Tilting the mower the wrong way
  • Too much engine oil
  • Contaminated air filter
  • Stuck carburetor float needle
  • Damaged carburetor diaphragm
  • Blown head gasket
  • Worn piston rings

Tools You Need For This Job

Some tools you may need to diagnose the problem of your lawn mower blowing white smoke include:

  1. Work gloves
  2. Screwdriver
  3. Carburetor cleaner
  4. Carburetor rebuild kit
  5. Clean rag
  6. Siphon

Lawn Mower Blowing White Smoke: Causes, Diagnosis, and Fixes

1. Tilting Mower The Wrong Way

Tilting your mower wrongly can allow oil to seep into the wrong places and cause your mower to blow white smoke.

Did you tip your lawn mower over to change the blade or perform some routine checks? Chances are you tilted it the wrong way. 

Similarly, if you mowed on a hill/slope steeper than 15 degrees, oil might have gotten on the engine. In this case, restarting the mower and letting the oil leak burn off will solve the issue. 

Fix:

Always tilt your mower with the air filter side facing up.

If you just recently mowed up a hill, start the engine and allow it to run till the smoke stops.

2. Contaminated Air Filter 

If you recently worked on your mower and tipped it over for any reason whatsoever, the air filter may be contaminated with oil. 

The white smoke may be a result of the engine heat burning off the oil on the filter. 

Diagnosis:

Remove the air filter housing and check the air filter. If it is soaked in oil, it has been contaminated and could be causing white smoke.

Fix:

Clean the air filter and let it dry, or simply replace it with a new one. Then, run the engine. The smoke should stop after a few minutes.

3. Too Much Engine Oil

Adding too much oil to your mower can cause the mower to blow white smoke. If you recently topped up the oil in your mower, this is most likely the problem.

The lawn mower has an oil dipstick. This dipstick has a line marked ‘Full’ indicating the maximum level of oil you should put in your mower. Putting in oil to exceed this mark will be excess.

Diagnosis:

Take off the dipstick cap, give the stick a quick wipe with a clean rag, and then put it back into the reservoir. 

Once more remove the stick, and check the oil level in relation to the stick’s recommended “Full” line.

If it exceeds it, the oil is in excess.

Fix:

Drain the excess oil out of the mower and make it so that there’s just enough oil in the mower.

To do this,  drain out all the oil (your owner’s manual will have instructions), then add more oil gradually to the reservoir. 

Once you’ve added roughly 3/4 of the amount suggested in the handbook, you may start using the dipstick to check the oil level. 

Keep adding tiny amounts of oil until you reach the ‘Full’ Mark indicated on the dipstick.

4. Stuck carburetor float/needle valve

White smoke usually indicates that there is liquid in the engine mixing up with oil. In a lawn mower, the only liquid that could be mixed up is gas.

The float needle regulates the amount of fuel going out of the carburetor. It closes to stop fuel flow when there is enough in the carburetor. 

It can get stuck in the open position with debris from stale fuel and cause excess fuel to leak out of the carburetor into the engine crankcase. 

This can cause white smoke to blow out of your mower’s engine. 

Diagnosis:

Take out the carburetor and check the needle. If it is stuck, broken, or worn, it could be a problem.

Fix:

  • Drain out the old gas if it has gone stale
  • Drain out old oil if it appears thin or smells of fuel 
  • Clean the carburetor and float needle with a carburetor cleaner
  • Add a fuel shut-off valve to the fuel line to stop fuel flow when the engine is not in use 

5. Damaged Carburetor Diaphragm

Another reason your engine can get flooded with fuel and blow white smoke is a damaged carburetor diaphragm.

The diaphragm of the carburetor aids in controlling the amount of fuel in the fuel mixture. It is constructed from a rubbery substance that can become stiff by repeated exposure to heat and fuel.

To perform its duties effectively, it needs to be flexible. The diaphragm will overfill the engine and flood it if it becomes too stiff or damaged, causing white smoke.

Diagnosis:

To check the diaphragm, remove the carburetor and open it up. It is a flat rubber item that is supported by a spring.

If it appears to be stiff, bent, or curved, it is damaged.

Fix:

Install a new diaphragm in the carburetor. Check the spring that supports it, if it is flat and doesn’t pop up, replace it.

6. Failed Head Gasket/Worn Piston Rings

Seals on the valves and pistons separate the combustion chamber from the oil crankcase in a mower’s engine. 

The head gasket and piston rings are put in place to make this separation effective. This is because gas and oil are not allowed to mix up.

The piston rings seal the combustion chamber so that there is minimal loss of gases to the crankcase. 

Likewise, the head gasket seals the engine’s combustion chamber and keeps oil from leaking into unwanted places in the mower engine.

A failed head gasket or worn piston ring will result in oil and gas getting into areas of the engine they aren’t needed and when the engine tries to burn them off, white smoke will blow out of your mower.

Diagnosis:

Inspect the piston rings and head gasket of the engine. Check if they are split, soaked with oil or gas, or worn out.

You can consult a small engine mechanic for assistance if you do not have much technical knowledge.

Fix:

Replace the blown gasket and piston rings with new ones.

Causes Of White Smoke In A 4-Stroke Engine 

All the problems mentioned above can cause a 4-stroke engine to blow white smoke.

Overfilling the crankcase with oil, operating the engine at greater than a 15-degree angle, blown head gasket, worn cylinder or piston rings, stuck carburetor float needle or a damaged diaphragm are all causes of white smoke in a 4-stroke engine.

Causes Of White Smoke In A 2-Stroke Engine

White smoke blowing from a 2-stroke engine is usually because the oil and fuel have mixed up. 

Most 2-stroke engines will blow white smoke especially as it starts up because of the mixture of gas and oil being burned. The oil that doesn’t get fully burned comes out of the exhaust as smoke.

The root of this problem is typically a leaking cylinder head gasket or O-rings.

Is White Smoke Blowing From My Lawn Mower Dangerous?

If your mower is brand new and emitting white smoke, there is no need to get worried. It is a sign of oil circulating into different parts of the engine.

It is best to keep the engine running for about five minutes to burn off the oil. If you turn off the mower, the smoke will return as soon as you restart it. 

If your mower is old, white smoke blowing from your lawn mower’s engine indicates that the oil is in excess or the engine needs to be serviced. 

You will need to troubleshoot to find and fix the problem. If you decide to keep using the mower that way, the engine may eventually begin to lose compression and power.

Furthermore, oil can damage other parts of your mower like the air filter and spark plugs, and can also harm engine parts that aren’t meant to come in contact with oil.

In terms of health, white smoke can be very harmful to the user. Inhaling white smoke continuously when moving can cause respiratory problems to the user and also people around.

Conclusion

Your lawn mower may be blowing smoke as a result of tipping it the wrong way, too much oil, a contaminated air filter, a damaged head gasket, a worn piston ring, or a damaged carburetor diaphragm or float needle.

To solve this problem, take your time to examine the mentioned parts and then apply the recommended fixes once you have identified the cause of the white smoke problem.