When does white smoke appear from the exhaust pipe of a diesel engine?

Smoke of different colors can come out of the exhaust pipe of a diesel engine: black, blue, gray, white. Each of these shades is clearly distinguishable when exhausted. Car owners are often interested in why a diesel engine smokes.

For high-quality control over the functioning of the power unit, it is necessary to conduct a thorough analysis of the shades and colors of the exhaust gases. The color of the diesel engine exhaust provides comprehensive information about the condition of the engine components and parts.

This allows you to eliminate malfunctions in the systems and components of the power unit, check the condition of the parts of the cylinder-piston group, gas distribution mechanism, eliminate failures of nozzles, fuel injection pump elements, etc.

Main signs of normal operation of a diesel engine

White smoke from the exhaust pipe of a diesel engine is a product of combustion of the air-fuel mixture, which is in a gaseous state. With optimal settings, a warmed-up diesel engine does not smoke. Normal engine operation is accompanied by the release of white water vapor, noticeable in winter when the ambient temperature is low.

The appearance of shades in diesel exhaust gases indicates a malfunction in the power unit. The color of the exhaust gas can be in various options:

• white-gray;
• gray;
• grayish blue;
• black smoke with soot.

Filters

You know, the last reason could be faulty (clogged) engine air filters. I also thought that this was not possible - but it is a fact! The thing is that there is less air (dirty filters do not allow it to pass), but there is more fuel, and the “smoke” increases. But here, not only white but also black exhaust can appear. But this is a topic for another article, be sure to follow our blog.

In the end, I want to say - if you have such a “whitish fog” effect in winter, the fluid level does not drop, then this is normal! You shouldn't even pay attention to this.

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How to distinguish white smoke from water vapor

To determine what quality of smoke comes out, you need to bring a white sheet of paper closer to the outlet of the pipe of a warm engine. Water stains quickly evaporate, leaving the paper clean. Bold marks on the paper indicate the presence of oil inclusions in the exhaust.

Smoke containing oil fragments is thicker and has a characteristic burning smell. When oil is present in the exhaust gases, increased consumption of engine oil is observed.

Prevention of "disease"

• check the antifreeze level in the expansion tank. Both using sensors and directly looking at the tank.
• antifreeze should not go away and change greatly in volume, but it needs to be updated - ideally, at least once a year

Even on cars with decent mileage, adding coolant is required little and rarely. If you need a new dose of antifreeze before each trip, your next destination is a service center. Preferably, official, with smart specialists and equipment. Because it's a serious matter.

The antifreeze has “evaporated” again - urgently go to the service center!

Are you waiting for a sign from above to help you realize that you can’t delay any longer?! Here he is! The faster the symptom of white smoke from the exhaust pipe is cured, the “less bloodshed” (less expense and nerves) you will get away with.

It is better, of course, that such serious problems do not happen in your auto history. So take care and love of your car and it will love you back.

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Exhaust gas formation process

Diesel fuel, being under high pressure, is injected into the cylinders through a special sprayer - an injector. The diesel fuel is sprayed into small fragments in the cylinder. The smallest particles of diesel fuel are heated in the combustion chamber and actively evaporate.

The operation of a four-stroke engine takes place in several stages:

1. Obtaining a sprayed portion of fuel at a given time both at idle and when operating under load, when the cylinder piston is in the upper position, i.e. at the moment of compression.
2. Self-ignition of the air-fuel mixture due to compression and high temperature.
3. Complete combustion with maximum return of useful energy to the piston.
4. Exhaust gases exiting the cylinders.

What color is the exhaust considered normal?

The exhaust gases of diesel and other engines are “products” of combustion in the cylinders of the working mixture, these are exhaust gases. When a diesel engine is running normally, without interruptions, smoking is possible immediately after starting. Once it warms up, the color of the exhaust becomes virtually transparent. During the cold season, white smoke is steam, usually caused by condensation. A faulty motor can produce smoke of the following colors:

• Thick black (with soot)
• Gray (gray with blue)
• White (grayish tint)

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Causes of white smoke

When warming up a cold diesel engine, the release of white smoke is normal, since this is water vapor formed during the evaporation of condensate formed from the air while the car is idle. Some moisture pours out of the exhaust pipe when the engine starts, the rest of the water evaporates.

As all parts of the exhaust system warm up, moisture and steam completely disappear. In winter, the release of steam is longer and more intense due to the slow heating of components and parts.

White smoke appears for the following reasons:

1. Increased humidity of components and parts of the exhaust system when warming up.
2. Inadequate combustion of diesel fuel in cylinders.
3. Faulty glow plugs.
4. Insufficient compression level in the cylinders.
5. The flash in the combustion chambers occurs with some delay.
6. Failure of the fuel pump plungers and bushings.
7. Penetration of coolant into the engine cylinders.
8. Presence of condensate in the exhaust system.

Diesel smokes white exhaust

Fuel injection of a diesel unit means that fuel is supplied to the cylinders under high pressure through a diesel injector. As diesel fuel passes through the nozzle, a so-called spray pattern is formed, due to which the supplied fuel is evenly divided into small drops in the diesel cylinder. Next, the sprayed fuel particles inside the cylinder are heated, and their active evaporation begins.

A fully operational four-stroke diesel engine in any operating mode (idling or under load) of the unit receives an effectively atomized portion of fuel at a clearly defined moment after the compression stroke in the engine cylinder. Next, the mixture self-ignites due to heating. Afterwards, the fuel-air working mixture of diesel fuel and air burns completely, giving maximum useful energy to the piston. The result is the release of exhaust gases from the cylinder. White smoke from a diesel engine pipe occurs for the following reasons:

• increased humidity in the exhaust system during warm-up;
• fuel may not burn completely in diesel cylinders;
• coolant entering the internal combustion engine cylinders;

Condensation in the exhaust system

For the warm-up mode of a cold engine, white exhaust from a working diesel engine is normal. In fact, the white color comes from water vapor in a car's exhaust system. Water condenses from the air after the machine is idle. After starting the engine, part of the condensate flows out in the form of water droplets and collects at the end of the exhaust pipe, while the other part of the water begins to evaporate. After heating the exhaust system of a diesel or gasoline engine, water and condensed steam usually disappear. The exception is the winter period. The lower the temperature outside, the longer and more intense the vaporization occurs. The reason is that the exhaust system heats up noticeably slower in cold weather.

Diesel does not burn completely

Also, white exhaust during warming up of the diesel engine occurs due to untimely self-ignition of the working mixture in the cylinder. The whitish-gray color of the exhaust indicates the presence of gases that should have pushed the piston in the cylinder, but ended up in the exhaust.

Note that this phenomenon is characteristic of both a serviceable diesel engine during the warm-up process in winter and a faulty diesel engine. In the first case, diesel fuel enters the cylinder and evaporates, but complete combustion of the mixture does not occur, taking into account the fixed angle of fuel supply. This is caused by insufficient temperature inside the cylinder for timely ignition, which immediately goes away with the heating of the internal combustion engine and is not a malfunction.

The appearance of white exhaust with a grayish tint on a fully warmed-up diesel engine indicates deviations from the norm. The reason is the same delay in self-ignition of the fuel in the combustion chamber as a result of an impaired fuel supply angle, but this occurs after the engine has reached operating temperature.

If the diesel smokes white, this indicates that the diesel injectors are supplying and spraying diesel fuel normally. Flash delay leads to a decrease in the temperature in the cylinder, the speed and uniformity of combustion of the mixture decreases, regardless of the efficiency of fuel atomization by the nozzle. In this case, the white color of the diesel engine exhaust indicates:

• problems with glow plugs;
• compression drop in cylinders;
• wear of injection pump plunger pairs;
• increased injection pressure of injectors;

We also recommend reading the article about the design of the diesel engine power system. From this article you will learn about the design features, components and operating features of the fuel system of a diesel internal combustion engine.

With such malfunctions, the diesel engine begins to experience difficulty starting “cold” and/or “hot”; the diesel engine may stall and operate unstably at idle and under load. The power unit loses power, acceleration dynamics decrease, fuel consumption increases noticeably, and the internal combustion engine’s response to pressing the gas pedal becomes less clear.

Coolant in cylinders

The presence of very thick white smoke in the exhaust of a heated diesel engine can be caused by coolant entering the engine cylinders from the cooling system of the power unit. The color of the exhaust may change, since the presence of antifreeze or antifreeze in the combustion chamber causes the diesel engine to smoke white, grayish or white-blue smoke. This depends on the components that make up the coolant in the cooling system. The density of the smoke is also affected by the outside air temperature (at negative temperatures, the exhaust becomes thicker).

The main cause of diesel smoke in this case is the water contained in the coolant. It actively evaporates from contact with heated components. The result is copious amounts of fog from the exhaust pipe. This malfunction is especially dangerous for a diesel engine compared to a gasoline car. The sulfur content in diesel fuel is increased, the temperature in the cylinder is high, and the ingress of water from the coolant leads to the active formation of sulfur oxide. The presence of sulfur dioxide has a detrimental effect on the service life of the diesel engine and associated systems.

Coolant will enter the cylinders as a result of the fact that the cylinder block (BC) gasket may be punctured, deformed, or burnt out. Another common cause is a crack in the cylinder head (cylinder head) or in the cylinder block itself. Liquid can also enter the internal combustion engine cylinder through the intake system. This is caused by a leaky intake manifold gasket, if this is structurally possible on a particular engine.

Additionally, liquid penetration into the cylinders can be diagnosed by monitoring the condition of the cooling system, checking the coolant level, as well as by the presence of exhaust gases (gas plugs) in the engine cooling system. To do this, simply unscrew the radiator cap or expansion tank. The smell of exhaust gases and/or an oil film on the surface of the coolant will indicate the diagnosis. When liquid enters the cylinders, the level will naturally decrease. If you start a cold engine without tightening the expansion tank cap, then the pressure in the cooling system will increase, the coolant level in the expansion tank will rise, but will be unstable. Gas bubbles will also appear in the tank, and coolant may spray out of the filler neck of the tank.

If the engine is turned off, fluid from the cooling system will begin to enter the cylinder, pass through the piston rings and end up in the engine oil. This is how antifreeze gets into the engine oil pan. Gradually the oil will mix with the coolant. The result will be the appearance of an emulsion. The engine oil itself becomes visually lighter and loses its luster upon contact with the liquid. The beneficial properties of the oil are lost. Penetration of the emulsion into the lubrication system will cause the appearance of a characteristic light brownish-yellow foam. This foam will be deposited on the valve cover and oil filler plug.

Small microcracks mean that there may be no signs of gases and oil entering the cooling system. The amount of coolant in the engine oil in case of such damage is not large, the oil may look clean, the process of foaming under the valve cover plug is present, but it is not intense.

More serious damage leads to active accumulation of coolant in the space above the piston, which makes it difficult to start the internal combustion engine (heavy rotation of the crankshaft by the starter). Excessive coolant leaks into the cylinder can lead to water hammer, bent connecting rods and major repairs.

It should be added that such problems are often associated with previous overheating of the diesel engine. In parallel with eliminating the main problem, the cooling system may also require a thorough inspection. It is necessary to ensure the functionality of the thermostat, radiator, radiator and expansion tank caps, cooling fan, serviceability of the fan switch sensor, integrity of the pipes and reliability of connections.

The dangers of incomplete combustion of diesel fuel

Partial combustion of diesel fuel results in a smoke-white color. An untimely flash of air-fuel mixtures in the cylinders leads to the release of whitish-gray gas, which did not have time to fully push the piston and ended up in the exhaust pipe.

In working diesel engines, this happens when starting the engine in winter. The temperature in the cylinders is not sufficient for self-ignition, the diesel fuel evaporates and the mixture does not burn completely. This is not a defect, since the smoke completely disappears as the engine heats up.

A serious deviation from the norm is characterized by the appearance of a white-gray exhaust when the engine is warm. Here, self-ignition is observed with a delay due to untimely supply of diesel fuel by the injectors, but the engine temperature at the same time has a sufficient operating value.

If the injectors supply and spray fuel without delay, but white-gray smoke is still released, the air-fuel mixture does not burn completely due to a decrease in temperature in the cylinders due to poor quality glow plugs, a decrease in pressure levels, and defects in fuel pump parts.

These malfunctions lead to the following problems:

• difficulties that arise when starting the power unit, both cold and warm;
• the appearance of a tripping effect in a diesel engine;
• engine instability at idle and under load;
• drop in power unit power;
• deterioration of acceleration dynamics;
• increased fuel consumption;
• decreased engine response to the gas pedal.

Blue or gray smoke

The most likely cause of blue (“oil”) smoke is oil getting into the engine cylinders. “Oil” smoke can have different color shades: from transparent blue to thick white-blue. This depends on the operating mode of the engine, the degree of its warming up and the amount of oil entering the cylinders, as well as lighting and other factors. It is noteworthy that oil smoke, unlike steam, does not dissipate quickly into the air, and the paper test mentioned above produces greasy droplets flying out of the pipe along with the exhaust gases. It is also obvious that oil smoke is accompanied by increased oil consumption. Thus, at a consumption of about 0.5 l/100 km, bluish smoke appears mainly in transition modes, and when it reaches 1.0 l/100 km, also in uniform motion modes. By the way, in the latter case, during transient conditions, oil smoke becomes thick blue-white. True, owners of the most modern cars need to remember about the possible presence of a neutralizer that can clean the exhaust gases from oil even at fairly high costs.

Oil can enter the combustion chambers (cylinders) in two ways: from below, through the piston rings, from above, through the gaps between the valve stems and guide bushings. The most likely reason for the appearance of blue exhaust is wear of the cylinder-piston parts. The upper compression rings experience wear not only on the outer surface in contact with the cylinder, but also on the end planes that perceive the gas pressure in the cylinder. The grooves of these rings in the pistons may also be worn out. Large gaps in the grooves create a pumping effect. Even if the oil scraper rings are still normal, oil still enters the cylinders, since the upper rings continuously “pump” it from the bottom up.

Cylinders wear out the most in the stopping zone of the upper ring when the piston reaches top dead center, and in the middle part they often take on an oval shape. Deviation of the cylinder shape from the circle impairs the sealing properties of the rings. Gaps usually form in the area of ​​the locks, but it is possible that they may appear in other places around the circle.

There are cases when, although the ring and piston are in relatively good condition, the cylinder surface is damaged. This happens, for example, when oil filtration is poor, when abrasive particles get between the piston and cylinder skirts, resulting in scratches on the cylinder. A similar situation is real after a long period of parking, when traces of corrosion may appear on the surface of the cylinders and rings. It will take considerable time to smooth out these defects and to mutually break in the parts (if they can break in at all).

The same effect often occurs when engine repair techniques are violated, when the surface of the rebuilt cylinder is too rough or the cylinder is of the wrong shape, or they used poor quality pistons or piston rings that do not meet the engine specifications. In such cases, normal engine operation should not generally be expected.

Wear of the cylinder-piston group is often accompanied by a loss of compression and an increase in pressure in the crankcase, which is determined by the corresponding devices (compressometer, leak tester, etc.). However, remember that a large amount of oil entering the cylinders well seals the gaps in the mating parts. If the gaps are not too large, then the result of the compression assessment can be quite normal, sometimes even closer to the upper limit. It is this circumstance that confuses the search for specific causes of oily blue smoke.

When there is no significant wear of parts, then blue or blue-white smoke is clearly observed only when the engine is running in warm-up mode, gradually decreases and even disappears altogether. The reason is simple: when heated, the parts expand and occupy more space, in which they are pressed harder against each other. If there is excessive wear, the picture is the opposite: the amount of smoke on a warm engine will increase, since it is easier for hot oil, which has a low viscosity, to enter the cylinder through worn parts.

It is always easier to identify a fault if it is associated with more severe forms of wear or even broken parts. Thus, significant detonation can occur, which leads to damage to the bridges between the rings on the pistons, at least damage to the rings themselves is most likely. Severe overheating of the engine causes deformation of the piston skirt, creating a large gap between the piston and the cylinder. A deformed piston warps, disrupting the operation of the rings. The same result is possible when the connecting rod is deformed, for example, due to water hammer when water gets into the cylinder or after a belt breaks and the piston hits an open valve.

Using low-quality oil can lead to ring burnout or sticking in the piston grooves. The use of low-quality oil can cause the rings to burn and stick in the piston grooves. And due to prolonged glow ignition, the rings can simply be rolled into the grooves with a complete loss of mobility.

The above defects usually do not occur in all cylinders at once. It is not difficult to find a faulty cylinder by comparing the condition of the spark and compression plugs in different cylinders. Moreover, such defects are often accompanied by various kinds of noise and knocking, which change with speed, load and degree of engine warm-up, as well as unstable engine operation due to cylinder shutdown (especially during a cold start). A common group of problems that cause oil smoke and oil consumption are associated with wear of valve stems and guides, as well as wear, mechanical defects and aging (loss of elasticity) of valve stem seals. These defects, as a rule, give a noticeable increase in engine smoke as it warms up, since the diluted hot oil passes much more easily through the gaps between worn parts. In addition, oil penetration into the cylinders increases at idle and during engine braking. In these modes, a large vacuum occurs in the intake manifold, and oil flows along the valve stems under the influence of a pressure difference, accumulating on the walls of parts and in the exhaust system. Subsequent opening of the throttle valve at the first moment sharply increases the density of the blue oil smoke.

For turbocharged engines, oil consumption accompanied by blue smoke is possible due to a malfunction of the turbocharger, in particular wear of the bearings and rotor seals. Wear of the front bearing seal of the compressor gives a picture similar to the failure of the valve stem seals (including oil deposits on the spark plugs), but at the same time a puddle of oil collects in the compressor inlet pipe. A turbine seal failure is difficult to determine because the oil goes directly into the exhaust system and burns out there.

In operation, blue smoke and oil consumption often appear when one of the cylinders is turned off due to an ignition fault or when the valves are leaking. In the latter case, the smoke becomes white-blue, especially if the valve has an obvious burnout. Such a defect is easily determined - the compression in this cylinder is insignificant or completely absent, and abundant black soot appears on the spark plug, often in the form of growths.

What is the effect of coolant entering the diesel combustion chambers?

When liquid from the cooling system enters the combustion chamber of a heated diesel engine, an exhaust saturated with thick white smoke appears from the pipe. The color of the smoke may change from white to gray as the antifreeze burns. The components that make up the coolant affect the color of the exhaust gases. The density of the smoke depends on the ambient temperature; in cold weather, the exhaust has a thicker consistency.

The water in the antifreeze actively evaporates, hitting the hot parts, and comes out of the pipe in the form of abundant fog.

The diesel engine especially suffers from this malfunction: diesel fuel becomes more saturated with sulfur, which leads to the formation of a colorless gas with a suffocating odor - sulfur oxide. When operating under such conditions, the service life of a diesel engine sharply decreases due to the rapid failure of its elements.

Consequences for the engine

Diesel is too complex and does not have a safety margin, so any malfunctions must be corrected immediately.

A decrease in power and an increase in fuel consumption can be considered only indirect symptoms of a malfunction that do not have critical consequences. What happened later would be much worse.

The thermal regime of the motor and the lubrication conditions for the most critical parts are disrupted; rapid wear leads to catastrophic breakdowns.

The cost of repairing a thoroughly damaged engine cannot be compared with the imaginary benefits of operating it with the above faults.

How to find the cause of engine overheating

If the engine is constantly heating up and white smoke is coming out of the muffler pipe, you should first check:

• oil in the engine crankcase, it should be a normal dark color. White or too light color of motor oil indicates that antifreeze or antifreeze got into it, and an emulsion formed when mixed;
• heating of the radiator pipes, when the upper hoses of the cooling system are hot and the lower hoses are cold, the thermostat is most likely faulty and the coolant flows in a small circle;
• presence of coolant in the radiator; if there is little of it, you should immediately turn off the engine, wait until it cools down a little, then add antifreeze to the cooling system.

Also, the cooling system can “air up”, but as long as the cylinder head gasket is sealed, almost no white smoke comes out of the muffler pipe. When the gasket overheats, it breaks through quite quickly, so you can’t drive with an elevated temperature in the cooling system; you need to look for the cause and eliminate the defect.

How to check the thermostat

Very often, the cause of engine overheating is a faulty thermostat. The valve does not open and does not allow the coolant to flow in a large circle, as a result of which the engine gets very hot. Checking the thermostat is easy, but to do this it must be removed from the engine. We check as follows:

• take a small metal dish;
• pour water into it;
• place a thermostat in the container;
• put the pan on the fire, you can place an electric boiler in the water;
• heat the water.

Trouble-shooting

Eliminating this problem largely depends on the type of motor.

1. Diesel car.

In the case of diesel engines, the problem may go away after the engine warms up. If this does not happen, then the cause of the problem may be water getting into the fuel.

The solution in such a situation is to replace it.

If a malfunction of the engine is detected, for example, damage to the cylinder head, it is necessary to replace the failed part.

Please note that it is impossible to repair cracked heads (even cast iron ones).

This is especially true if the crack is located between the valve seats.

Be sure to check the cooling system for leaks.

2. For carburetor (for example, VAZ-2101) and injection (for example, VAZ-2109) cars, the actions should be as follows:

• If you have diagnosed the appearance of steam from the exhaust pipe, then wait until the engine warms up. Perhaps this is ordinary steam, which, after reaching the optimal temperature, will become invisible;
• Remove the cylinder head and inspect the gasket, as well as nearby surfaces. If there is a defect in the gasket, then the product must be replaced;
• If the gasket is intact, then check the block head for leaks. As a rule, the appearance of microcracks is characteristic of areas near the valve seats;
• check the integrity of the cooling system - radiator, tank and connecting pipes;
• inspect the cylinders for cracks. If any are found, the part must be replaced.

The actions described above are usually typical for diesel cars.