What You Need to Know About White Smoke from Your ATV

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The exhaust smoke color can be a helpful indicator of your ATV engine’s health and often acts as a warning sign when there’s a problem. White smoke can be alarming and may indicate a severe issue that needs further investigation.

Some white smoke is normal. However, if the white smoke persists after the engine heats up, it is usually caused by a leak allowing coolant into the combustion chamber, where it turns into steam.  

In this post, we look at the different causes of white smoke from an ATV, how harmful it can be, and how you can fix it. 

How Does Exhaust Smoke Turn White?

A healthy modern 4-stroke ATV engine should not emit any visible signs of exhaust smoke after it has reached normal operating temperature.

The gases from the exhaust are the by-product of the combustion process that happens inside the engine. 

A carefully calibrated mix of air and gas gets introduced into the combustion chamber, where it gets ignited by the spark to make the engine run. 

When everything works as it should, with optimal and uninterrupted combustion, all of the fuel gets ignited, and the exhaust gasses become colorless. 

Discoloration of the exhaust smoke can happen when a foreign substance gets introduced into the combustion chamber and interferes with the normal combustion process.

When you see white smoke coming from your ATV’s exhaust, it’s typically caused by one of two things: steam created from evaporating water or a sign of oil burning off inside the engine.

Different Types of White ATV Exhaust Smoke and Their Causes

There are several grades of white smoke, each with its possible causes and fixes. 

To learn whether the white smoke coming from your ATV is normal or a sign of a severe issue, carefully observe how the smoke looks and behaves and compare your findings to the variations listed below. 

Wispy White Smoke at Startup

If you’re from somewhere with a warmer climate, you might not be used to white exhaust smoke from your vehicles at startup. 

However, for those living in colder climates, a little bit of smoke is an everyday phenomenon that usually doesn’t raise much concern.

Some wispy white smoke from the exhaust the first 30 seconds or so after starting an ATV in colder climates is caused by steam and is entirely normal.

However, if the smoke does not subside, or when the ATV displays this behavior in warm weather, it could indicate a problem with the engine.

White smoke after startup is often explained by evaporating condensation that has built up inside the exhaust overnight. While this may contribute to the phenomenon, it is not the primary cause. 

Gasoline is a hydrocarbon fuel; as the name indicates, it is made up of compounds of carbon and hydrogen.

When gasoline combusts, the hydrocarbon reacts with oxygen and turns into carbon dioxide and water. The heat from the combustion vaporizes the water and turns it into steam.

Without getting too technical, hot steam is invisible, but when it cools down, it condensates and turns into a visible mist or cloud of microscopic droplets.

As the hot steam from the combustion enters the cold exhaust system, it cools down, and when it hits the cool air outside, it forms the visible steam we perceive as white smoke. 

How much vapor turns into visible steam depends on the outside temperature and air humidity. The cooler and more humid the outside air is, the more likely it is to turn the water vapor into visible white steam. 

Some of the vapor condensates into liquid water inside the exhaust pipes. More water will build up if you leave the ATV idling to warm up.

The water inside the exhaust system eventually vaporizes as the hot exhaust heats the exhaust pipes to operating temperature. 

When the exhaust pipes heat up, they no longer cool down the exhaust gasses as much.

The vapor from the muffler now holds a much higher temperature and is not as likely to condense and turn white before it dissipates into the air. 

Thick White Smoke 

If the white smoke persists after the engine has had time to heat up, you might face a potential engine problem.

Plumes of thick white smoke billowing from your ATV’s tailpipe after the engine heats up are usually caused by an internal coolant leak into the cylinders or cylinder head. The coolant contains water that vaporizes when it enters the combustion chamber. 

Several potential issues could cause coolant to enter cylinders.

  • A Breach in the head gasket (most common)
  • A bad intake manifold seal.
  • Worn valve guides or worn valve stem seals.
  • Cracks in the cylinder head.
  • Cracks in the cylinder.
  • Cracks in the engine block (rare).

Using your nose is one way to confirm you have a coolant leak. Assuming your ATV uses glycol-based coolant, it should smell slightly sweet when you smell the exhaust fumes. 

Other signs of a coolant leak are an abnormal drop in the coolant level or the ATV overheating due to low coolant levels. 

You could also check for engine oil in the coolant or coolant in the engine oil:

Check for coolant in the oil: Remove the dipstick and examine the oil. Healthy engine oil should have a clear, dark brown color. If you notice foamy, froth-like bubbles in the oil, it could indicate the presence of coolant mixed with the oil.

Check for oil in the coolant: With a cold engine, remove the radiator cap or coolant reservoir cap to inspect the coolant. Healthy coolant has a clear, bright-colored appearance, while coolant mixed with oil creates an oily foam. 

You could perform a compression test on the cooling system to confirm any suspicions of a coolant leak. To do a test, you need a radiator pressure and leakage test kit that replaces the stock radiator cap to pump coolant into the system under pressure.

To fix an internal leak, you might need a complete engine rebuild or possibly new engine components if there are any cracks.  

After rebuilding the engine, you need to do a coolant flush to remove contaminants from the cooling system.

Bluish White Smoke

While most people wouldn’t describe this form of smoke as white, I’ve included it in the overview to eliminate the risk of confusion. 

Bluish-white or bluish-grey smoke is caused by oil burning off inside the combustion chamber. Two-stroke ATVs use gas with oil added to it, and some smoke is normal. However, bluish-white smoke from a four-stroke ATV is not normal and needs to be addressed.

If you’re riding a two-stroke ATV and feel it produces too much bluish-white smoke, you should ensure you haven’t mixed too much oil into the gas.

It is essential to mix according to manufacturer recommendations. Too little oil can seize the engine, and too much oil will cause the engine to run lean and produce excessive smoke.

Also, make sure to use the correct type of oil. Regular engine oil is too heavy and can cause excessive smoke if used in a 2-stroke engine.

Note that it is normal for a two-stroke engine to produce more smoke when cold due to leftover fuel and oil causing the engine to run rich. Using the choke adds to this. 

However, a correctly jetted two-stroke engine should not smoke much when it has reached operating temperature. 

Blueish-white smoke in a four-stroke ATV indicates engine oil has somehow entered the combustion chamber.

This can happen if you fill it with too much engine oil. Check the oil level and drain some oil if the oil level is above the max.

Another common cause is stuck piston rings not sealing properly, allowing oil from the crankcase to squeeze past the piston into the combustion chamber. 

The white smoke will sometimes subside as the engine heats up, allowing the piston rings to seal better. 

Stuck piston rings may come loose over time, but using an engine cleaner additive to speed up the process is better. 

Other, more severe causes involve mechanical engine wear, allowing oil to enter the cylinder head:

  • Worn or damaged cylinder, piston, or piston rings.
  • Worn valve guides or valve stems.
  • Bad valve stem seals.

An indicator that your engine burns oil is when the engine oil level drops over time.

In less severe cases, it might be something you are willing to live with. In more severe cases, you might need an engine rebuild.

Before tearing down the engine, there are several tests you can do to get an indication of where the leak is coming from. 

You can read more about the causes of blue smoke and how to troubleshoot them in this post.

Bleach-White Smoke Smelling of Gas

This final type of white smoke only happens in sporadic cases. 

When plumes of bleach-white smoke that smells of gasoline come out of the exhaust, it is usually caused by a malfunction in the ATV’s fuel delivery system, sending excessive amounts of fuel into the combustion chamber.

The white smoke from unburnt fuel vaporizing smells has a distinct smell of pure gas because that is what it is. 

The most common cause of gas-smalling white smoke is fuel injectors stuck in the open position, allowing too much fuel to enter the engine. Another potential cause is incorrect fuel injector timing or low cylinder compression.

In a worst-case scenario, the gas vaper could ignite from a glowing red hot exhaust pipe, causing an explosion that would blow the exhaust pipe clean off the vehicle. 

Due to the distinct smell of gas that always comes with this type of smoke, there is rarely any chance of mistaking it for smoke caused by coolant leaks. 

Is White Smoke From an ATV Harmful?

White smoke that goes away when the ATV heats up is harmless and should not raise concern. However, white smoke caused by coolant leaks, unwanted oil in the gas, or unburnt gas can harm the engine. 

Coolant leaks can cause the ATV to overheat when the coolant level drops below the minimum level. Check this post to learn the symptoms of an overheating engine. After identifying and repairing the coolant leak, you must replace the O2-senor, which is now contaminated with antifreeze. 

Smoke caused by oil in the combustion chamber is an early sign of an engine problem that, if left untreated, can lead to more severe damage, potentially a complete engine failure. 

What to Do if Your ATV Puts Out White Smoke?

As soon as you notice your ATV begins to put out abnormal white smoke, the main thing to do is stop and not ride any further.

Do not attempt to ride the ATV back home, as this may cause additional damage to the engine. 

After towing your ATV back home, it’s up to you to troubleshoot and repair the issue yourself or take it to a mechanic.

How Do You Fix White Smoke From the ATV Exhaust?

Most of the time, eliminating the issues causing white smoke requires an engine tear-down.

While we’ll save how to rebuild an engine for later, it is essential to remember that it is not enough to fix the issue; you also need to find the root cause.

For example, with a blown head gasket, you need to know what caused the gasket to fail in the first place. Common causes include overheating, pre-ignition and detonation, abrupt temperature changes, or old age. 

With worn piston rings allowing oil to slip past the piston, you must also ensure the air filter is in good condition and seated correctly so that sand and dust cannot enter the air intake. 

How to Prevent White Smoke

The best way to prevent your ATV from developing an issue that could cause white exhaust smoke is to keep up with the scheduled maintenance and upkeep.

Haavard Krislok
Haavard Krislok
Haavard Krislok is an ATV and off-road enthusiast with a rich background spanning two decades in owning, maintaining, repairing, and utilizing ATVs for farming, logging, and hunting. Outside his professional life as an engineer and project manager, he cherishes recreational trail riding and is the creative force behind BoostATV.com, serving as its owner, editor, and content creator.

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