Why is My Lawn Mower Blowing Blue Smoke?

The most important piece of equipment you own to take care of your lawn is your mower. Mowing your grass regularly at the right height and at the right interval will keep it healthy and looking its best. So if you notice your mower smoking, it’s easy to be concerned. Mowers can be expensive to repair or replace. The good news is that usually blue smoke isn’t as bad as it looks. Lawn mower blowing blue smoke?

Let’s identify the problem and tell you what you need to know to fix it.

It Can Happen to Anyone

Sometimes, even if you use your lawn mower with extra care and caution, follow my recommendations for spring lawn mower maintenance, and winterize your mower properly, you might encounter issues.

That may leave you scratching your head and asking, “What could be wrong with my lawnmower?” 

It’s important not to blame yourself – these things happen. Look at it as an opportunity to learn, so you can avoid the same issue in the future.

There are many indicators that your lawn mower needs a tune-up or perhaps needs to be retired and replaced. Maybe your mower isn’t starting properly, or you notice a vibration or wobble during use.

But this article focuses on one issue, and that’s what to do when you see blue smoke coming out of your lawn mower. What’s the cause, how do you know for sure, and what should you do to fix it?

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What Causes Your Lawn Mower to Blow Blue Smoke?

Seeing your lawn mower blowing blue smoke can be concerning.

This is especially true if it’s something that you haven’t encountered before, or you don’t consider yourself a pro at fixing stuff. The good news is it’s probably a simple, minor issue:

If blue smoke is coming from your lawn mower, it typically means that your machine is burning excess oil. If you wait it out for 10-15 minutes, the blue smoke should soon dissipate. You probably just need to wait until the extra oil burns off.

Often, this is something that you should not worry about, nor does it require any repair service.

However, it is also essential to understand what caused your lawn mower to billow blue smoke so you can take the necessary measures to prevent it from happening again.

Let’s not make this a habit, eh?

Below are some of the common reasons your lawn mower blows blue smoke, and what you can do to make sure it doesn’t keep happening.

Oil Spill on the Engine

Excess oil may spill onto the engine when you change the oil in your mower. Then, when you fire up the mower, the spilled oil will burn on the hot engine and generate smoke.

The simple solution to this is to let the spilled oil burn off, which will take just a few minutes (and a few concerned looks from your nosy neighbors).

The same thing can happen if you’ve overfilled the mower’s oil reservoir.

Checking the Oil Level

To check the oil level, use the dipstick in the reservoir. Just remove the dipstick, which is attached to the bottom of the cap, then wipe it dry with a clean rag. Insert the dipstick back into the reservoir. Remove the dipstick once again and check the oil level against the “fill” line on the stick.

It’s important to do this check when your mower has been sitting still and before starting the motor. Otherwise, you will not get an accurate reading because the oil will have sloshed around.

If the oil level is too high, you can drain the oil by tipping the mower on its side.

Drain a small amount of oil into a safe container, then check the level again with the dipstick. You can repeat the process until the oil reaches the correct level, as seen on the dipstick.

Finally, run the mower to burn off the excess oil. When the smoke clears, your lawn mower is good to go.

Another way to drain oil from the reservoir is by unbolting the sump plug. However, note that not all lawn mowers are built with a sump plug (check your manual to be sure).

If your lawnmower doesn’t have one, you can use an oil extractor pump to drain oil. Oil extractor pumps are available in most mower shops, and you can buy them online as well (here’s one on Amazon).

Mower has been Tipped on its Side

Sometimes, engine oil can make its way to the cylinder if you tip your mower at a 15-degree angle.

This can happen if you tilt the mower when inspecting under the deck or when you’re replacing the blades. Using your lawn mower on a steep slope may also cause the oil to spill.

You can solve this problem by letting the engine run idly to allow the spilled oil to burn off and smoke to clear.

If you tip your lawn mower for cleaning or maintenance, it is also always a good idea to check the owner’s manual to determine the best ways to reduce oil leaks. Most mowers are designed to tip to one side, but not the other, so consult your manual for best results and to avoid oil getting where it isn’t supposed to go.

Usually, you only want to tip walk-behind mowers toward the oil cap. This is how many of these mowers are designed to have the oil drained.

Oil Residue in New Lawn Mowers

Perhaps you’ve recently bought your first lawn mower (or upgraded from an old one), and when you started the engine, it smoked.

Don’t panic. Sometimes, residual oil may be found in brand new lawn mowers. This is usually the reason why your brand new mower is smoking.

Just let your mower run for up to 15 minutes, then the smoke should clear.

The above issues should not be a cause for alarm. However, if after 15 minutes, smoke continues to billow from your new mower, then you might be dealing with a more serious problem.

Returning and exchanging it for another mower may be your best bet.

Bigger Problems Causing Lawn Mower to Blow Blue Smoke

Here are a few problems you should look out for when troubleshooting blue smoke from your mower.

Typically you’ll only see these issues with older mowers.

Damaged Head Gasket

The head gasket is usually in between the cylinder head and the cylinder block of the mower’s engine. Its main purpose is to keep the engine blocked off from oil or other elements.

If your lawn mower has a blown head gasket, the smoke won’t likely disappear even if you try to drain oil from your mower’s reservoir. Since it’s not sealing the cylinder as it should, oil can leak into it. That oil will burn and give off smoke.

If your lawn mower’s head gasket is damaged or cracked, you’ll need to replace it with a new one.

This is a job for a pro, and it can be expensive. Check to see if your mower is under warranty. If not, get a price from a local small engine repair shop – that’s where you’ll probably get the best deal.

Defective Crankcase Breather

The crankcase breather, also known as the PVC valve, traps gases that escape during combustion to relieve pressure and reduce buildup of corrosive material in the lawn mower’s engine.

If it doesn’t work properly, it may cause damage to other parts of your lawn mower. It may also allow pressure to increase, causing blown seals and gaskets which result in oil leaks.

Replacing the crankcase breather is the best solution and it is relatively fast and easy, without need to tear your lawn mower’s engine apart.

Worn Out Piston Rings

The piston rings of a lawn mower seal the combustion chamber, keeping the oil engine from accessing it. Piston rings may get worn out from frequent use or if the mower is poorly controlled. They may also get damaged if your lawn mower’s air filter is dirty and unable to block dust and other debris.

Not replacing the engine oil in your lawn mower frequently may also result in poor lubrication and cause the piston rings to dry and crack.

Unfortunately, there’s no quick and easy fix if your lawn mower’s piston rings are worn out, damaged, or faulty. Your best option may be to have the entire engine replaced, and depending upon your mower’s value, it may be time to go shopping.

Why Your Lawn Mower is Blowing Blue Smoke

Your lawn mower blowing blue smoke is usually caused by an oil spill or leak. If the smoke clears in less than 15 minutes, then the oil spill is small enough not to cause any major damage to your lawn mower.

The tips and information I’ve shared in this article should help most people diagnose their problem, and prevent any reoccurrence.

However, if your lawn mower continues to blow blue smoke after 15 minutes, you might want to call in a professional small engine repair service for help. Alternatively, if your mower is still covered by warranty, then you can have it checked by the manufacturer.

Either option will probably be less expensive than getting a new one. The biggest cost will be time lost while your mower is in the shop, but you can always ask a neighbor to borrow their mower for a week if needed.