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Snowblower Smoking – Time to quit!

By: Author John Cunningham. Published: 2023/06/13 at 9:35 am

Walking behind a smoking snowblower is no fun and is a health risk; luckily, the causes of smoke are easily fixed, and I’ll bet that’s the case with your snowblower. I’m John Cunningham, a qualified mechanic, and very shortly, we’ll have this figured out.

Seven common causes of Snowblower smoke include:

  1. Snowblower turned over incorrectly
  2. Drive belt issue
  3. Overfull oil level
  4. Oil leak
  5. Overheating engine
  6. Fuel contamination
  7. Engine wear issue

In this post, you’ll learn all the common causes of Snowblower smoke and how to identify the likely cause by the color of the smoke and by the smell; let’s jump right on in.

Snowblower Smoke Identification

Smoke is smoke, right? Yeah… not really; I put smoke into one of four buckets. Worth noting most come from the exhaust. They are:

Snowblower Blowing White/Grey Smoke

White smoke

White-grey smoke from the exhaust is commonly associated with oil in the combustion chamber.

Snowblower Blowing Black Smoke

Black smoke

Black smoke from the exhaust is commonly associated with a fueling issue.

Snowblower Blowing Blue Smoke

Blue smoke from the exhaust is commonly associated with an engine wear issue.

Snowblower Blue/Black Smoke & Burning Smell

Remove pulley cover

Blue/black smoke from the crankshaft pulley cover & a burning smell is commonly associated with a belt issue (auger or drive belt).

Now let’s get into the most common causes of smoke.

1 Snowblower Turned Over Incorrectly

Snowblower on its side

Snowblower turned over incorrectly is one of the easiest causes of smoke to solve and is also the more usual cause of a snowblower that suddenly starts to smoke like a mad thing.

However, if your engine has been smoking for some time and seems to be worsening, you can skip to the next section, as this won’t apply to your machine.

OK, so what’s wrong with tipping the snowblower over on its side? Sometimes, you may get away with this if you tilt your blower over with the carburetor side facing up; however, face it the other way, and gas and oil can sometimes sneak into the combustion chamber.

The oil and gas are burnt off on start-up, causing a cloud of white/grey smoke to bellow from the exhaust. Now, the smoke looks dramatic, but no harm done.

The Fix

Start the engine, and the smoke will clear; just let her run for a few minutes but don’t labor the engine… I’d check the wind direction first, or your neighbors may get their panties in a bunch.

When the smoke clears, check the oil level, add a drop if needed, and you are back in business.

Check out this post – Check snowblower oil level.

You may find this post helpful; it’s about correctly turning over your snowblower for storage or repairs – Putting snowblower on its side.

2 Belt Issue

Your snowblower typically has two drive belts, one to power the wheels (Transmission drive belt) and the other to power the auger (Auger belt). Belts are made from synthetic rubber, cord, and fabric; the very best belts employ a Kevlar wrap that makes them super durable.

Drive belts

The thing is with belts, they work really hard and are under a ton of stress; any small issue with a belt will quickly make itself known.

The more usual symptoms of a belt issue include a reduction in drive speed at the wheel or an auger that lacks Ooomph when it hits the snow.

The life of a belt varies from machine to machine, but you can expect to get five years plus from your belts. If you’d like to know more about snowblower belts check out – How long do snowblower belts last?

The usual root cause of drive issues is a worn belt; sometimes, the belt is loose and may be adjusted, but typically, the belt is loose because it’s worn out and needs replacing.

So where’s the smoke coming from?

A loose belt smokes because the rotating crankshaft pulley is heating, melting, and burning the now stationary drive belts instead of actually driving them. If this is our problem, then you can recognize it by the acrid smell of burning rubber, the big tell-tale, of course, is smoke coming from under the crankshaft plastic shield.

The fix

Access the belts by removing the crankshaft plastic protective shield and inspecting the belts. Both belts typically incorporate a mechanical belt tensioner to apply tension when needed. The drive belt is typically tensioned all the time, but the auger belt tensioner is typically applied with the auger control on the handlebars.

Drive belt tensioner

The drive belt that powers the wheels should always be taut.

And the auger belt only be when the auger control lever is applied.

Auger belt

Have a helper apply the auger handlebar control or improvise (engine off) and see if the belt is taut.

Belt smoke likely means our belt is flat spotted, a concept familiar to motor racing fans; it’s when a wheel locks up and wears down a small contact patch. The problem now is vibration; even if the belt were good pre-flat spot, it is now junk. The flat spot sets up a vibration in the machine and will likely derail the belt.

Anyhow, if you think this is your problem, I’ve covered replacing both belts previously in these posts – Auger belt stops when hit snow, and Drive system diagnosis.

3 Overfull Oil Level

A little oil can’t hurt, right? Well… a little too much can cause problems. I have a neighbor who, every season, if his snowblower needs it or not, gets an oil top-up. Eventually, the inevitable happened, she wouldn’t start, and he complained of a super stiff pull cord as he tried to get her running.

Yep, he filled her up all right.

Oil too full

Too much oil can cause a no-start, and that’s on the happier side of the spectrum. If you are unlucky, adding too much oil paradoxically causes insufficient oil flow inside the engine, and that can do some real spendy type damage.

Splash paddles connected to the crankshaft hit the surface of the oil, splashing the oil all over the innards. Overfilling submerges the paddles, meaning – no splash, more of a mixing action that compounds the problem by adding air pockets (bubbles) in the oil.

In the middle of the spectrum, we have smoke bellowing from the exhaust, that’s the engine burning off the excess oil as it tries to continue operating; so in this case, smoke is a good sign, but only if we don’t ignore the message.

The fix

Shut her down, allow the oil to settle in the oil pan before checking the oil level. If you are way above the full make, we’ll need to drain some out. I have covered this procedure previously, and you can check that out here – Draining excess engine oil.

Now, if you overfilled it accidentally, no harm done; just run the engine after removing the excess oil. She’ll smoke a little for a minute or so, but then you’ll be back in business. However, if you didn’t overfill it, the oil stinks of gas, and you can’t explain why……suspect a carburetor issue, which I cover below.

4 Overheating Engine

Running the engine for long periods at full tilt can cause the engine to overheat, even in low temperatures. The overheating can allow oil to enter the combustion chamber, and you already know it causes smoke.

The fix here is usually simple – take a coffee break and let her cool her heels. Before getting back at it, check the oil level, a low oil level is the most common cause of overheating.

A machine that shows signs of overheating with just normal use suggests an issue. An airflow restriction around the carburetor intake would do it, snowblowers don’t use air filters, but you could check for debris around the carburetor intake.

Engine fan

Snowblowers are air-cooled and use fan blades fitted to the flywheel to move air around the engine. If the blades are restricted or broken, the engine will overheat.

Something as simple as a loose spark plug, the wrong plug type, or the wrong fuel type can cause overheating issues. Using E15 fuel could cause overheating as small engines typically don’t like it; they’ll tolerate E10 at most, and E85 will kill your engine. Stale gas can cause overheating as it losses its Oomph.

Inflate tire

Something as simple as a flat tire can cause a machine to work harder and could be the root cause of overheating.

There are other possible causes, like vacuum leaks and valve train issues, but your engine should exhibit other issues like hard starting and rough running in addition to the smoke.

5 Fuel Issue

Small engines don’t care for E15 or E85 gas in fact, older machines hate it, and manufacturers will void your warranty if they suspect the damage was caused by said fuel. E15 can cause engine performance issues and smoke. E10 is acceptable but can still cause issues, especially with summer storage.


Ethanol is hard on the carburetor plastic and rubber components and also causes gumming. Gumming is a congealed mess that develops inside the carburetors when they are left idle over the summer months.

Carburetors employ a float and a valve to control the fuel supply to the carburetor from the gas tank. It’s, for most snowblowers, a simple gravity feed system. Problems arise when the rubber sealing tip of the valve fails; it causes the fuel from the gas tank to migrate to the crankcase and dilutes the engine oil contaminating it.

To prevent this problem in the future, use a fuel stabilizer; it protects those seals and prevents gumming, check it out here – Fuel stabilizer mixing & adding

And as you already know, an engine will attempt to burn off excess oil in the crankcase, and that will cause white smoke in the process.

Some other tell-tale signs of a leaking valve include a strong smell of gas in the garage, maybe fuel on the floor, unexplained gas loss from the tank, gas inside the cylinder, and fouled flooded plug.

Anyhow, I’ve covered the fix previously, and you can check it out here – Snowblower oil smells like gas.

6 Oil Leak

Oil leaks happen as an engine gets a few years on it, especially so when machines are stored in minus temperatures. The extreme cold causes the engine to contract, and the seals allow a little oil to sneak past, evidenced by the garage floor’s damp patch.

Starting the engine causes the engine to expand, and the seals are again doing their job. But the escaped oil may be pooled on the engine or have been splashed onto a hot surface such as the exhaust, where it will burn and cause fumes or smoke. This isn’t a common explanation for smoke, but I have seen it.

To diagnose, go ahead and look for evidence of oil leaks; depending on how bad the leak is or long it persists, you may need to replace the seal. Worth noting oil leaks are often caused by too much oil in the crankcase, so I’d eliminate this first by checking the oil level.

Oil seal

The most common oil leaks include a crankshaft seal leak and a cam rocker cover gasket leak. I’ve covered replacing the crank seal previously, it’s a mower, but the process is the same – Replace lawnmower crankshaft seal

7 Engine Wear

Engine wear is generally a common cause of engine smoke and is more expensive to repair. In my experience, snowblowers engines typically last a long time; they work hard, sure, but not for very long. Not a bad life!

But engine wear is not directly associated with how often or hard an engine works; a significant factor is maintenance. How often is the oil changed? Oil, as you know, lubes the engine’s innards, helping cool it, neutralize nasty acids, and clean the inside of the motor.

Oil drain

That takes a toll on oil; it no longer does its job if not changed. And old oil turbocharges engine wear, no matter how few hours are on the engine.

A compression test will tell if engine wear is the root cause of the smoke; engine wear smoke is typically blue. And if the blue smoke is only on startup, it’s valve stem seals causing the issue, and that’s a pretty common cause. The seals prevent oil from entering the combustion chamber, but as seals age, they harden and allow oil to sneak past.

An oil conditioner added to the oil often helps soften the seals rejuvenating them, but they can be replaced easily enough too.

For compression testing, check out the compression test video here.

Other Possible Issues

Now there are some other causes, and we’ll just touch on them below; some are more serious than others.

  • Ignition system issue – Something as simple as a faulty spark plug can cause black smoke or indeed, any ignition system fault. An intermittent ignition causes misfires and unburnt fuel, evidenced by black smoke from the exhaust.
  • Head gasket issue – A gasket can allow oil to sneak into the combustion chamber and cause a ton of smoke.


The common causes of smoke include incorrect tipping, belt issues, overfull oil, oil leaks, engine overheating, fuel problems, and engine wear.

By identifying the color and smell of the smoke, we can pinpoint the likely cause. Solutions include letting the engine run to clear smoke, adjusting or replacing belts, draining excess oil, addressing overheating, using proper fuel, fixing leaks, and performing maintenance.

You may find the following links helpful: