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There are only 5 possible reasons why white smoke comes out of a car exhaust pipe. Two of them do not depend on us, respectively, they cannot be eliminated. Luckily, they don't show damage. The third reason is related to the mode of operation of the car, and also, in general, is not a malfunction. But the last two causes of white smoke from the exhaust system are already problems. One is due to lack of maintenance, and the other is due to a serious breakdown of the internal combustion engine.

Exhaust smoke chemistry

Fuel combustion reaction
Fuel combustion reaction

To understand the nature of the formation of white smoke, the easiest way is to turn to elementary chemistry. Of course, it is incorrect to call those processes that occur in a car during the combustion of fuel simple. However, for the study of our question, much can be simplified. But in the end, we will get an almost complete understanding of what white smoke is, and why it is of that color.

The smoke from the exhaust system of a car is a product of the combustion of the air-fuel mixture in the engine. Our fuel consists, to put it simply, of two chemical elements - H (hydrogen) and C (carbon). It also includes various corrosion inhibitors, dyes, cleaners and other "chemistry". She is of little interest to us. The main thing is that there is hydrogen and carbon.

In order for the fuel to burn in the engine, it must be supplied there in certain proportions with air. There is O (oxygen), N (nitrogen) in the air, as well as other components that are also not of great interest to us. The components of air do not burn on their own. However, the combustion of fuel is nothing more than its oxidation. This requires oxygen, which is contained in our air.

Now, let's get the spark going.

The air-fuel mixture prepared in advance and supplied to the combustion chamber ignites. During combustion, the bonds between the hydrogen and carbon atoms in the fuel are destroyed. Due to this, a large amount of energy is released, which, roughly speaking, “pushes” the piston down. The car went, and we continue to monitor what is happening inside the engine.

Hydrogen atoms detached from our fuel combine with oxygen residues, forming the well- known H 2 O. That is, water. However, not in the form in which we see it and use it every day. Do not forget that in the combustion chamber, due to the combustion of fuel, there is a very high temperature at which water can exist only in a gaseous state. That is, in the form of steam. He is what we need.

For those who are interested, the simplified formula for burning gasoline in a car engine is as follows:

HC4 + 2O2 = 2H2O + CO2

Visualization of the chemical process of fuel combustion
Visualization of the chemical process of fuel combustion

That is, as a result of the combustion of fuel in the combustion chambers, a mixture of gases flies out of the exhaust pipe, which includes:

  • water in the form of steam (H2O);
  • carbon dioxide (CO2);
  • nitrogen (N);
  • other components that are part of the air and fuel, but do not burn.

Despite such a “rich” composition, in general, the combustion products of gasoline or diesel are colorless and transparent. At least that's how they should be in ideal conditions. However, quite often white smoke comes out of the exhaust pipe, and it does not differ in transparency. There is also a black exhaust, but that's another story.

White smoke: causes

White smoke is not smoke
White smoke is not smoke

Why is exhaust smoke sometimes white? There are several common reasons for this. Generally speaking, in all known cases the cause is the same. Namely: since the combustion products of fuel always contain water, the white color is given to them by nothing more than its vapor. It's just that under ideal conditions, water vapor has such a weak concentration that it is in fact transparent and invisible.

If the smoke is thick and white, then this (either one thing, or all together):

  1. Low ambient temperature.
  2. High ambient humidity.
  3. Condensation in the exhaust pipe.
  4. Dirty air filter.
  5. Coolant in combustion chambers.

For complete clarity, we propose to analyze each of these reasons in more detail. This will allow you to understand the nature of white smoke from the exhaust pipe, and also help to find out, in one case or another, the cause of its appearance. After all, if the car smokes "due to the fault" of the environment, then this is not a problem. But, for example, there is no place for coolant in the combustion chambers, and if it got there, then you should be able to calculate it.

Low ambient temperature

Smoke? No. Steam.
Smoke? No. Steam.

The most common cause of white smoke from a car exhaust pipe. When temperatures drop below 0°C outside, the water vapor encounters conditions where small particles of water freeze abruptly. Since there are countless of them, we see them in the form of a white thick fog. The same thing happens when we exhale air in winter - water vapor leaves the lungs heated, and when it comes into contact with street air, it freezes sharply, forming a dense vapor.

It should be noted that in winter, only unheated cars “smoke” with white steam. When the engine warms up along with the exhaust system, the exhaust becomes almost transparent. This is because the water vapor, together with the products of combustion, is heated so much that immediately after leaving the pipe it does not have time to freeze. The transformation does not disappear, however, already at a distance from the car, where the concentration is no longer the same, and the conditions are completely different.

How to determine that the cause of white smoke from the exhaust pipe is precisely the low ambient temperature, and not something else? Firstly, steam is observed only in severe frost, and at positive temperatures it is not visible. Secondly, the exhaust becomes transparent (or almost transparent) as the engine and vehicle exhaust system warm up. If there is no frost on the street and the car has already worked for a long time, and white thick smoke does not disappear, then this is not the reason.

High ambient humidity

High humidity is one of the causes of white "smoke"
High humidity is one of the causes of white "smoke"

The second common cause of thick white exhaust vapor is high humidity. The same air that is sucked in by the engine to prepare the air- fuel mixture. And the more humid the air, the more water it contains in an already “ready” form. In the combustion chambers, it evaporates, and is added to those vapors that were formed as a result of the decay of fuel atoms. As a result, the concentration of water vapor in the exhaust is so high that we can observe it in the form of thick and dense puffs of the so-called white smoke. By now it should be clear that this is not exactly what is commonly called smoke.

We can observe this kind of white steam from the exhaust pipe in several cases. Like when it's foggy outside. This atmospheric phenomenon is accompanied by a sharp increase in humidity in the air. The same thing happens when it rains. In the mornings, the humidity of the air is also increased, as the dew that settled during the night evaporates from the surface of the Earth. Etc.

It is clear that there is nothing wrong with such white smoke from the exhaust. It does not indicate any malfunction, but is simply part of the natural processes. Immediately disappears as soon as the wet weather is replaced by dry. In addition, if the humidity is not too high, then white smoke can be observed when the engine is cold, and as it warms up, the exhaust becomes transparent.

Condensation in the exhaust pipe

Water in the exhaust pipe evaporates when heated
Water in the exhaust pipe evaporates when heated

By and large, this cause of white smoke from the exhaust pipe also does not belong to the category of malfunctions. It only indicates that condensate has previously accumulated in the exhaust system. That is, water vapor has turned into liquid water. This happens when the car was driven for a short time, and the water vapor included in the exhaust gases did not have time to completely leave the exhaust system. When the engine is stopped, the exhaust pipe cools and the steam in it condenses. Drop to drop - and in some cases a lot of water accumulates.

If there is liquid water in the exhaust system, when the car warms up again, a thick white vapor will form. We can observe it. Moreover, regardless of the temperature and humidity of the environment. Actually, this reason is determined precisely on this basis: if it continues to smoke profusely after warming up in dry, warm weather, then there is water in the system.

There are only three ways to eliminate this cause of white smoke. The first is incorrect, and consists in drilling a hole in the muffler to let water out. Under no circumstances should this be done. Over time, due to corrosion, the hole will turn into a hole, the sound of the car will not change for the better, and even later the exhaust system will have to be changed.

The second common way to remove water from the exhaust system is to remove the muffler. You can do this, and many, in fact, do it. However, there is a third, more natural and adequate way to remove water from the exhaust system. All that is needed for this is to regularly drive a long distance by car. The water will evaporate on its own, and the thick white smoke will disappear. Naturally, if you have nowhere to go for a long time and far, then, of course, the accumulation of water and the subsequent disassembly of the exhaust system cannot be avoided.

By the way, in order to evaporate water from a car muffler, it is not at all necessary to warm it up due to meaningless long trips. You can warm up the system from the outside. Fortunately, a building hair dryer is not a luxury today. At the very least, it will cost much less than constant runs just to remove water from the exhaust system.

If you drive a lot regularly, and thick white smoke comes out of the exhaust, then water in the muffler is not your case. See other reasons.

Dirty air filter

Few people know, but a dirty air filter also leads to the formation of white smoke.
Few people know, but a dirty air filter also leads to the formation of white smoke.

The air filter is designed to clean the air that is used by the fuel system to prepare the air-fuel mixture. When it becomes excessively clogged, its throughput decreases. As a result, the fuel system receives less air, which is why it prepares an enriched air-fuel mixture. It absolutely also contains all the components necessary for the formation of water vapor.

However, since there is not enough oxygen for the complete combustion of the fuel, it burns incompletely. As a result, we have not only increased fuel consumption, but also denser thick white vapor from the exhaust pipe. Of course, unburned carbohydrates are not completely white, but gray or bluish. However, together with natural water vapor, already thick visible smoke is formed.

For those motorists who have experience, determining the fact of the enrichment of the air-fuel mixture by the shade of the exhaust is not a problem. Beginners quite often confuse such smoke with ordinary steam. Especially after learning that a common cause of white smoke is frost or high humidity. As a result, the problem is not given due attention.

Coolant in combustion chambers

If the white smoke is thick and there is a lot of it, it is evaporating coolant
If the white smoke is thick and there is a lot of it, it is evaporating coolant

In conclusion, the most unpleasant cause of white smoke from the exhaust remained. The internal combustion engine is designed in such a way that its cooling liquid does not come into contact with either the fuel or its combustion products. However, due to gasket breakdown, thermal deformation, or other breakdowns, antifreeze or antifreeze can enter the combustion chambers. And since ordinary water predominates in its composition, during the combustion of the fuel it evaporates intensively, and together with the combustion products it flies out into the exhaust pipe in the form of thick clouds of white smoke.

It is possible to understand that the cause of white smoke is the ingress of coolant into the combustion chambers by several indirect signs:

  • smoke is very plentiful;
  • does not stop in any weather;
  • smokes heavily when the engine is warm;
  • the exhaust has a sweet smell (it smells like evaporated ethylene glycol or other alcohol that is part of antifreeze);
  • the coolant level in the expansion tank drops (often gradually, imperceptibly);
  • the coolant has lost its transparency, has become dark, cloudy, foamy, and so on;
  • increased fuel consumption;
  • engine idle speed began to float;
  • starting the engine is more difficult.

Additionally, suspecting the coolant in the formation of thick white smoke from the exhaust pipe, you can check this in the old-fashioned way. Namely, with the help of a clean, dry cloth, which must be brought to the muffler outlet for a few seconds. If the exhaust contains only pure water vapor, among other natural debris, the cloth will first become damp, and after a while (away from the muffler) it will dry and remain clean.

A simple test for the presence of antifreeze vapors in white smoke
A simple test for the presence of antifreeze vapors in white smoke

If moisture remains on the napkin for a long time, try it by touch. An oily, greasy consistency indicates that these are antifreeze components. It should also be understood that traces of engine oil may remain on the napkin. But this, again, is a completely different story - about black smoke from the exhaust pipe.

Brief summary

White smoke cheat sheet
White smoke cheat sheet


Cause of white smoke

Main features


Negative air temperature

It appears only in winter, in frosty weather. Disappears as the engine warms up.


High humidity

It manifests itself in wet weather (rain, fog), as well as in the early morning. Does not disappear even as the engine warms up, but does not appear in dry weather.


Liquid water in the exhaust system

It happens in cases where the car is often used for short trips. You can determine by the characteristic sound by shaking the muffler with your hand (carefully - the exhaust system may be hot).


Clogged air filter

It appears after long-term operation of the car in dusty air conditions. Also, in cases where the air filter has not been changed according to the regulations. The smoke is usually off-white. Slightly bluish or bluish.


Coolant entered the combustion chambers (chamber)

The exhaust is inadequately thick and dense. There are greasy marks on the napkin. Smoke does not stop either on a warm engine or in dry, warm weather. It goes away, cloudy or foamed coolant.


In most cases, white smoke from a car's exhaust system is not a problem. This is just water vapor, which is always contained in the air in one concentration or another. Things are a little worse if the cause of white smoke is liquid water in the muffler. However, this is not fatal either. A much sadder situation awaits when the cause of white smoke is coolant that has fallen where it should not. Here, as a rule, one cannot do without expensive and dreary repairs.

VIDEO: what your exhaust smoke is trying to tell you