Blue Smoke From Exhaust Pipe Lawn Mowers

In principle, many car owners do not pay much attention to smoke from the exhaust pipe if its amount decreases after the car has completely warmed up, and during movement the smoke disappears altogether. However, if the smoke does not stop even when driving, this is a clear sign of more or less serious malfunctions in the car’s engine.

Blue Smoke From Exhaust Pipe Lawn Mowers

The smoke from the exhaust pipe of the car signals to its owner about a malfunction

These problems seem to try to attract the attention of the driver, exacerbating when starting the engine and appearing in the form of smoke of various shades – white, black or bluish-gray. You should carefully consider these alarms and timely identify the malfunction before you need a complex and costly repair.

About the nature of exhaust smoke

The color and texture of the smoke from the exhaust pipe can be figuratively compared with the freshness of human breathing – a healthy organism (both biological and mechanical) exhales correspondingly cleaner vapors than the diseased one. In a working vehicle, when fuel is burned, compounds of water and carbon dioxide are formed – as in vapors from the breathing of a healthy person. However, it must be taken into account that gasoline combustion does not occur on pure oxygen, but with the help of ordinary air, mostly consisting of nitrogen.

That is why harmful nitrogen oxides (NOx) are formed in the smoke from the exhaust pipes of cars, which negatively affect the atmosphere and even lead to the so-called acid rain. And the fuel is not completely oxidized and burns out, even in engines of the latest brands, and because of this there is an additional emission of carbon compounds – CO and CH. In addition to all this, when oil or coolant enters the combustion chamber, other, no less harmful, chemical “cocktails” appear and go into the air.

Of course, the exhaust system of modern engines, if possible, is equipped with various converters and filters. However, this is not enough – remember the dense clouds of smog in the photographs of the largest cities. In addition, any filtering system wears out over time, thereby increasing the toxicity of smoke coming from the exhaust pipe of the car. Although, as mentioned above, the color and toxicity of smoke depend not only on the unsuitability of self-regulation mechanisms, but also on many other malfunctions.

Comparative characteristics of the exhaust gases of gasoline and diesel engines

Most often, more or less thick smoke from the exhaust pipe signals the car owner about the malfunction of the fuel supply and engine cooling systems, as well as about malfunctions of the distribution mechanism or piston group. Each of these cases has its own nuances: either the fuel burns out defectively, or coolant, and sometimes oil, enters the cylinders. As a matter of fact, it is the excess fuel or the presence of foreign substances in the cylinders that give the exhaust gases different shades.

In general, the color of the smoke from the exhaust pipe is almost the same – the differences are only in the nuances, because sometimes the malfunctions of a certain system that cause smoke are directly related to the malfunction of other systems that cannot "make themselves known" by smoke. For example, such a situation is not uncommon: the cooling system does not work well, because of which the engine overheats. Due to overheating, piston rings are burned, which entails the ingress of oil into the cylinders and, as a result, the appearance of smoke. Note that the original reason lies not in the piston rings, but in the cooling system.

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That is why, starting to look for the cause that caused the smoke from the exhaust pipe, it should be extremely careful – analyzing and comparing all available factors. The most common combinations of such factors and possible shades of smoke, we now consider in more detail.

The origin of white smoke

Often, especially in cold weather, during the warm-up mode of a cold engine, you can notice white smoke from the exhaust pipe. The appearance of a white cloud (which in fact is not smoke, but steam) is often associated with complete cooling of the engine overnight. Water vapor is a natural satellite of the fuel combustion process. When the exhaust system cools overnight, the water condenses, and as the system begins to warm up, the condensation of the water decreases and the warm evaporation becomes visible in the cold air. Thus, the density of white smoke directly depends on the ambient temperature: the colder it is on the street, the more visible the white cloud becomes. In addition, the degree of steam saturation is also associated with air humidity – with increased humidity, the steam thickens more.

Harmless white steam when warming the engine in cold weather

What indicator of a car’s “health” is the presence of such smoke from the exhaust pipe – good or bad? It depends on several points of consideration. Exhaust with enough water vapor indicates the efficient operation of the motor. However, with regard to the exhaust system itself, the intense formation of white steam cannot be called a good sign of its operation. If such steam appears even in warm weather, you need to check the cylinders for coolant getting into them. In this case, special attention should be paid to checking the tightness of the head gasket.

Video: Blue Smoke From Exhaust Pipe Lawn Mowers


Water is part of the coolant – and when it enters the cylinders, it does not have time to evaporate during the combustion of fuel, which leads to the formation of white smoke vapor. By the way, sometimes it can acquire an oily bluish tint – it also depends on the composition of the coolant. In general, it is easy to distinguish smoke from steam: steam dissipates almost immediately, and after smoke in the air there is a slight fog for some time. You should also know that the ingress of fluid into the cylinders leads to intense pollution of the spark plugs, from which they begin to spark, and as a result, the cylinder cannot work fully.

The density of white smoke depends on humidity and air temperature.

Also, the intense emission of white smoke from the exhaust pipe may indicate that the engine had not previously warmed up to the required temperature – for example, due to the fact that the car only moved for short distances. In this case, a certain amount of water remains in the muffler and exhaust pipes, which is “not good”, since it can lead to the appearance of foci of corrosion.

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Gray smoke (possibly with a bluish tint)

The next in our smoke classification will consider the gray smoke from the exhaust pipe. In most cases, the appearance of bluish and blue exhaust smoke is “oily” in nature. Typically, this situation is associated with the combustion of oil in the cylinders – most often this applies to cars of old brands, since their engines are already at a fairly high degree of wear. The cylinder walls in such motors are thinned, and therefore the piston rings are no longer able to provide proper sealing. As a result, the oil is poorly removed, its consumption increases, and the compression decreases – that is why the "tired" car begins to smoke with a gray or blue exhaust.

In some situations, when the wear of the motor is not yet critical, the cylinders can remain in fairly good condition, and the reason for the gray smoke coming from the exhaust pipe is only in the coked rings. Especially often, the rings are coked and, accordingly, lose mobility when the car has been running on low-quality fuel for a long time (the same applies to oil). One way or another, but with the appearance of bluish-blue smoke, the car owner willy-nilly should think about a serious repair with a complete exhaustion of the engine.

A gray exhaust can warn of wear on the piston rings …

However, there are less fatal causes – for example, valve stem seals that seal valve stems. Since they are made of rubber, they can also lose their pristine elasticity over time, which entails the leakage of oil. In these cases, the oil through the gaps enters the intake manifold, and from there into the combustion chamber, which is a condition for the appearance of a gray exhaust. Of course, if the case is in caps, then troubleshooting will cost the car owner much cheaper than a complete analysis and prevention of the motor.

Quite often, a problem arises when oil is consumed due to incorrect operation of the ventilation system, in this case, crankcase ventilation. In this case, the oil enters the crankcase due to the fact that the pressure in the cylinder rises so much that the piston seal can no longer cope with the exhaust gases generated by the combustion of fuel. It is “thanks to” overpressure and combustion of unwanted gases that uncharacteristic smoke appears from the exhaust pipe. The engine tries to pump the gases on its own, communicating with the intake system. Because of this, the gases are re-burnt, and then leave through the exhaust pipe. The main harm in this case is caused by the oil “fog”, which reaches for the gases inside the engine and interacts with its parts, which leads to the appearance of bluish-blue smoke from the exhaust pipe.

… Or problems with crankcase ventilation

The ventilation system is designed to cope with these undesirable processes: in good condition, it must separate the oil and regulate the flow rate (since the engine works on the principle of a pump and can create too high a vacuum in the intake system). So, if the ventilation is spoiled – oil consumption, respectively, increases. However, if we talk about the cost of eliminating this problem, then it is quite small, especially if the owner clearly understands what he is dealing with and does not allow himself to be deceived by the employees of the service station.

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Black smoke is the cause of fuel

As the name of this subsection shows, black smoke from an exhaust pipe most often owes its appearance to problems with fuel. The black color of the exhaust is due to the color of soot, which is formed as a result of, for example, incomplete combustion of fuel. Soot appears when the process of decomposition into elements of that part of the fuel, which did not have enough air for complete combustion, takes place.

Modern cars are equipped with computer systems that control all the processes that occur during movement – including the process of fuel combustion. Under such “sensitive guidance”, the risk of errors in the formation of a combustible mixture is significantly reduced – although by and large this applies only to gasoline engines, while a diesel engine, even the most modern one, will still be slightly smoked.

This is due to the fact that in diesel engines the composition of the mixture is different from gasoline counterparts – its concentration in this case is heterogeneous and contains impregnations of high fuel density. To give it uniformity, the modern auto industry uses mechanisms of increased injection pressure – however, even this measure is not yet able to completely eradicate the problem, and therefore smoke-soaked smoke from the exhaust pipe of a diesel engine car can be seen much more often than gasoline cars.

The black color of the smoke from the exhaust pipe is due to the presence of soot

Particulate filters are used on the latest brands, which to some extent solves the issue (however, these filters must be cleaned periodically, and sooner or later replaced with new ones).

In addition to incomplete combustion, other factors can also cause black smoke from the exhaust pipe – for example, insufficient quality of gasoline. It should be remembered that the use of low-quality gasoline can entail a too fast combustion process – this combustion is also called detonation. Another factor affecting the intense formation of soot may be the malfunction of the very notorious electronic system that monitors the efficiency of fuel combustion. For example, a failure of the oxygen sensor leads to the fact that the electronic unit is unable to monitor the completeness of combustion – and then it starts working at random, while not maintaining a full-fledged "dialogue" with the oxygen sensor.

Video – white smoke (steam) engine

Video – the appearance of blue smoke from the exhaust pipe

Video – Nissan Skyline cold start and black smoke coming out of it

The conclusion!

So, the smoke from the exhaust pipe, regardless of its color, should not leave the car owner indifferent – because, thus, the car signals a malfunction. We wish all our readers good cars and smokeless trips!