Engine smoke: causes and solutions

The appearance of smoke can be associated with malfunctions of various systems and working units of the engine: power system, cooling system, ignition system, injection control system, cylinder piston group, distributor mechanism and so on. According to the cause of the malfunction, smoke occurs either due to incomplete or improper combustion of fuel, or due to the ingress of coolant into the cylinders, or due to the ingress of oil, which gives the exhaust gases a characteristic color. Often a malfunction in one system, which turns out to be the source of smoke, occurs because of malfunctions and defects in another. Here is a typical example: poor operation of the cooling system leads to overheating of the engine and, accordingly, burning of piston rings. As a consequence, oil gets into the cylinders, which causes smoking. It is better to start the search for the cause with a comparison of all visible circumstances: the nature of the smoke, the observed accompanying phenomena, the possible influence of the external environment. Among experienced motorists there is an opinion that by the color of smoke from the exhaust pipe you can determine what kind of engine malfunction it is caused by.

Many people are familiar with the following situation: you start the engine after a long parking, and from the exhaust pipe – thick smoke. And even when warming up, the amount and color of smoke may decrease, and when driving and disappear altogether. But more often it happens otherwise. Smoke continues, the color of the smoke remains and clearly shows that the heart of the car ( engine )there are any problems. And the reason for this is not a long parking lot, but other reasons, and in this case, a long period of inactivity served as a push that aggravated the problems or led to their sharp manifestation.

Smoke from the exhaust pipe can be white, blue, black and any intermediate shades. Color serves as an important diagnostic sign. Engine operation with increased smoke is often accompanied by other deviations from the norm, although sometimes little noticeable on the kotryh driver pays attention only when the smoke of one or another color. Therefore, such signs should definitely be noticed and noted to more accurately assess the situation of serviceability and performance of the engine.

If you analyze the possible malfunctions, it turns out that in many situations the smoke is the same color, although it has different causes. Let’s first consider this issue in general terms, and then we will analyze each specific case in more detail and make this visual malfunction point us to more serious defects hidden from the eyes, i.e. by the color of the exhaust determine the condition of the car engine.

Table: Causes of smoke from the exhaust pipe and solutions

White or clear smoke from the exhaust pipe

White smoke from the exhaust pipe is quite normal when warming up a cold engine. But it should be taken into account that this is not smoke, but vapor. Water in a vaporous, steamy state – a natural product of fuel combustion, this is normal, and no action is required. The fact is that in a cold exhaust system, the vapor from fuel combustion partially condenses while becoming visible, with water (condensation) usually appearing on the edge of the exhaust pipe. As the system warms up, condensation decreases. The colder the environment, the denser, whiter and more visible the vapor becomes. At temperatures below -10 degrees Celsius white steam is formed on a well-warmed engine, and at a frost of -20 … -25 degrees the exhaust due to steam, acquires a dense white color with a blue tint. You can give an example of a familiar situation in winter when large cars or buses driving away from the stop, so smoky that you have to slow down for lack of visibility. The color and saturation of the vapor is also affected by the humidity of the air: the more it is, the thicker the vapor. It should be noted that water vapors after leaving the exhaust pipe dissipate quite quickly and do not smell anything.

Constant white smoke in warm weather and on a well-warmed engine, may indicate, most often with the ingress of coolant (water, tosol, antifreeze) in the cylinders (a possible place of ingress may be a leaky cylinder head gasket). In this case, the coolant moisture does not have time to evaporate completely during fuel combustion, which causes thick white smoke (high-density vapor). In this case, the shade of the exhaust depends on the composition of the coolant, the weather and the color of the ambient light. The shade of white smoke can be blue, resembling “oil” smoke, but it is still possible to distinguish if you look closely, water vapor, dissipates quickly, up to invisibility, unlike the “oil” smoke, which in the air for a long time remains a bluish mist.

Causes of white smoke from the tailpipe

First of all, it is necessary to make sure that it is steam that comes from the exhaust pipe, and not “oil” smoke. We do a simple action – warm up the engine to operating temperature, or even after a trip, briefly close the exhaust pipe opening with a white, clean sheet of paper and look, the water from the sheet will gradually evaporate and will not leave obvious greasy traces, and they will not be greasy to the touch. If there are obviously greasy, oily traces that do not disappear – the motor has another problem, not related to the leakage of coolant into the cylinders.

If there are no obvious oil marks on the sheet, search further. Fluid can get into the cylinder not only because of a damaged cylinder head gasket, but also because of cracks in the cylinder head or block. All these defects in the engine cause exhaust gases to enter the cooling system (in this case it is also possible to have a gas cap in the cooling system), which, if detected, will indicate the described problems. Look in the radiator or expansion tank: if the coolant has a distinct odor of burning (exhaust gases) and/or there is a thin film of oil on its surface, the cause of the white smoke is the ingress of exhaust gases into the cooling system. In such cases, after starting a cold engine, the pressure in the cooling system immediately increases (it is not difficult to feel it with your hand, squeezing the upper radiator pipe), and there is also an increase in the level of liquid in the expansion tank. And this liquid level is unstable, gas bubbles may appear in the expansion tank.

If the engine is stopped, the picture will change exactly the opposite. The fluid will start to go into the cylinder. Gradually it will leak through the piston rings and get into the oil, into the oil pan. On subsequent start-up, the oil and coolant will mix and form an emulsion that is light in color, regardless of oil production. The emulsion is not transparent; it gives the oil a cloudy appearance. Circulating through the lubrication system, such emulsion leaves a characteristic foam of light yellow-brown color on the head cap and oil filler plug. Such foam is formed in case of saturated emulsion, i.e. if the crack or blowout has a large area. If the crack or blowout is insignificant, foam formation is still possible, even with clear oil. If the leakage in the cylinder is significant, the liquid accumulating above the piston may prevent the crankshaft from turning at the first moment of starting. In particularly severe cases, there may be a hydrostroke in the cylinder, deformation and breakage of the connecting rod. Sometimes it is possible to detect a cylinder that leaks antifreeze by inspecting the spark plugs. The spark plug will look like a new one – the antifreeze literally washes it away. If you feed pressurized air into the cylinder through the spark plug channel (for example, through an adapter with a hose or a special leak tester), then the level of liquid in the expansion tank will begin to rise (when checking, it is necessary to turn the crankshaft to a position in which both valves are closed, put the car on the brake and turn on the gear). Further identification or repair of the malfunction is carried out with the removal of the cylinder head. It is necessary to assess the condition of the gasket, the planes of the head and the block.

It should also be borne in mind that the burnout of the cylinder head gasket is often accompanied by deformation of the head plane, especially if the defect was preceded by engine overheating. If no obvious defects are found, it is necessary to check the head for tightness under pressure. Most likely on the wall of the combustion chamber will be found a crack: more often near the seat of the exhaust valve. You should also carefully inspect the cylinder by lowering the piston to bottom dead center. A crack in the cylinder is a rare defect, but if there is one, it is not difficult to detect. The edges of the crack diverge and often end up polished off by the piston rings. It is also possible for coolant to enter the cylinder through the intake system, e.g. due to a leaky intake manifold gasket, if it also seals the manifold coolant heating ducts. In such cases, the pressure in the cooling system does not increase, there is no exhaust odor, but the oil turns into an emulsion, and the coolant level drops rapidly. These signs are usually enough to find the defect and not to confuse it with the one described above, otherwise the block head will be removed in vain. All malfunctions associated with white smoke from the exhaust pipe require more than just eliminating the direct causes. Since the defects are usually caused by engine overheating, then you should check and eliminate malfunctions in the cooling system – it is possible that the thermostat, on-off sensor, clutch or the fan itself is not working, the radiator, its plug, hoses or connections are leaking. If white smoke and accompanying defects are noticed, then it is impossible to operate the car. First, the defects quickly progress. And secondly – the work of the motor on the water-oil emulsion sharply accelerates the wear of parts and after a few hundred kilometers without major repairs, most likely, you can not do without.

Blue or blue smoke

The most probable cause of blue (“oil”) smoke is the ingress of oil into the engine cylinders. “Oil” smoke can have different color shades: from transparent blue to thick white-blue. This depends on the mode of operation of the engine, the degree of its warming up and the amount of oil entering the cylinders, as well as illumination and other factors. It is noteworthy that oil smoke, unlike vapor, does not dissipate rapidly in the air, and the above-mentioned test with paper gives greasy droplets flying out of the pipe with the exhaust gases. It is also evident that oily smoke is accompanied by increased oil consumption. Thus, at a consumption of about 0.5 l/100 km, blue smoke appears mainly in transient modes, and when reaching 1.0 l/100 km – and in modes of uniform driving. By the way, in the latter case, oil smoke becomes thick blue-white on transient modes. True, the owners of the most modern cars should remember about the possible presence of a neutralizer, which is able to clean the exhaust gases from oil even at sufficiently high costs.

Oil can enter the combustion chambers (cylinders) in two ways: from below, through the piston rings, and from above, through the gaps between the valve stems and guide sleeves. The most likely cause of blue exhaust, is the wear of parts of the cylinder piston group. At the upper compression rings there is wear not only on the outer surface in contact with the cylinder, but also on the end planes that take the pressure of gases in the cylinder. Can be worn and grooves of these rings in the pistons. Large gaps in the grooves create a pumping effect. Even if the oil rings are still good, oil still flows into the cylinders because the top rings continuously “pump” it up from the bottom.

Cylinders wear the most in the area where the top ring stops when the piston reaches top dead center, and often become oval in the middle part. Deviation of the cylinder shape from a circle impairs the sealing properties of the rings. Gaps are usually formed in the area of the locks, but it is not excluded their appearance in other places of the circumference.

There are cases when the cylinder surface is damaged when the ring and piston are in relatively good condition. This occurs, for example, with poor oil filtration, when abrasive particles get between the piston skirt and the cylinder, and scratches appear on the cylinder. The same situation is also real after a long parking period, when corrosion marks may appear on the surface of the cylinders and rings. It will take considerable time for these defects to smooth out and for the parts to work together (if they can work together at all).

The same effect often occurs when the engine rebuilder’s technique is not followed, when the surface of the rebuilt cylinder is too rough or the cylinder is irregularly shaped, or they have used poor quality pistons or piston rings that do not match the engine specifications. In such cases, normal engine operation should generally not be expected.

Wear of the cylinder piston group is often accompanied by loss of compression and increase in crankcase pressure, which are determined by appropriate devices (compressometer, leak tester, etc.). However, remember that a large amount of oil entering the cylinders seals well the gaps in the mating parts. If the gaps are not too large, the result of the compression evaluation 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 great wear of parts, then blue or blue-white smoke is clearly observed only when the engine is running in the warm-up mode, gradually decreases and even disappears altogether. The reason is simple: when warmed up, the parts expand and occupy a larger space in which they press harder against each other. If there is too much wear, the picture is the opposite: the amount of smoke on a warmed-up engine will increase because hot oil, which has a low viscosity, can more easily enter the cylinder through the worn parts.

It is always easier to identify a fault if it involves more severe forms of worn or even broken parts. Thus, significant detonation can manifest itself, causing 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 is the cause of deformation of the piston skirt, a large gap is formed between the piston and the cylinder. The deformed piston tilts, disturbing the rings. The same result can occur if the connecting rod is deformed, e.g. due to water hammering into the cylinder or after a belt break and the piston strikes a valve that has not closed.

The use of poor quality oil can cause the rings to burn or seize in the piston grooves. The use of low-quality oil can cause the rings to burn or seize in the piston grooves. And as a result of long caliber ignition, the rings can be simply welded in the grooves with complete loss of mobility.

The above defects usually do not occur in all cylinders at once. It is not difficult to find a defective cylinder by comparing the condition of the spark plugs and compression in different cylinders. Moreover, such defects are often accompanied by various kinds of noises and knocks that change with rpm, load and the degree of engine warm-up, as well as unstable engine operation due to cylinder deactivation (especially at cold start). A common group of faults that cause oil smoke and oil consumption are associated with the wear of valve stems and guide bushes, as well as wear, mechanical defects and aging (loss of elasticity) of oil caps. These defects tend to give a noticeable increase in engine smoke as the engine warms up, as liquefied hot oil flows much more easily through the gaps between worn parts. In addition, the ingress of oil into the cylinders increases at idle and when the engine is braked. At these modes in the intake manifold is a large rarefaction, and oil flows over the valve stems under the influence of pressure drop, accumulating on the walls of parts and in the exhaust system. The subsequent opening of the throttle at the first moment dramatically increases the density of the blue oil smoke.

In turbocharged engines, oil consumption accompanied by blue smoke is possible due to turbocharger malfunction, in particular worn bearings and rotor seals. A worn compressor front bearing seal gives a similar pattern to a failing oil cap (including oil soot on the plugs), but a puddle of oil collects in the compressor inlet. Failure of the turbine seal is difficult to determine, because the oil goes directly into the exhaust system and there afterburning.

In operation, blue smoke and oil consumption often appear when one of the cylinders is disconnected due to ignition malfunction or valve leaks. In the latter case, the smoke becomes white-blue, especially if the valve has a clear burnout. Such a defect is determined without difficulty – the compression in this cylinder is insignificant or absent at all, and on the candle appears abundant black soot, often in the form of growths.

Black smoke

Black smoke from the exhaust pipe indicates over-enrichment of the fuel-air mixture, and, consequently, about the malfunction of the fuel supply system. Such smoke is usually clearly visible against the light background behind the car and represents soot particles – products of incomplete combustion of fuel.

Black smoke is often accompanied by high fuel consumption, poor starting, unstable engine operation, high toxicity of exhaust gases, and often loss of power due to suboptimal composition of the fuel-air mixture. In carburetor engines, black smoke is usually caused by overflow in the float chamber due to a defect in the needle valve or due to clogging of the air jets.

In gasoline engines with electronic fuel injection, over-enrichment of the mixture appears, as a rule, with the malfunction and failure of various sensors (oxygen, air flow, etc.), as well as with leaky injectors. The latter case is dangerous with hydrostroke in the cylinder at startup with all the above-mentioned consequences. The essence is that through a faulty injector on an idle engine a lot of fuel can leak into the cylinder, and it will not allow the piston to approach the top dead center. In diesels, black smoke sometimes appears not only when the high-pressure pump malfunctions, but also when the injection advance angle is high. Common to the modes of operation of gasoline engines on over-refined mixture is increased wear and even scoring of parts of the cylinder piston group, because excess fuel washes oil from the cylinder walls and worsens lubrication. In addition, fuel enters the oil and liquefies it, worsening lubrication conditions in other mating engine parts as well. In some cases, this liquefaction is so great that the oil level in the crankcase (or, more precisely, the oil/fuel mixture) rises significantly. The diluted oil acquires a distinct gasoline odor. Obviously, the operation of the engine with such malfunctions is not only difficult, but also extremely undesirable, because it quickly leads to new, much more serious troubles.

So, black smoke tells us about the rich mixture of fuel. In turn, this pulls a failure in the power system or ignition, or in the malfunction of fuel injection control. Black smoke from the exhaust pipe is the result of improper combustion of the fuel mixture. It can be clearly seen in daylight, small particles of soot will be visible.

By the way, black smoke from the tailpipe is often accompanied by increased gasoline consumption, as well as increased concentration and toxicity of exhaust gases, the engine does not work properly – unstable, it does not start well, and often leads to deterioration of the dynamic qualities of the car. In carbureted engines, as already written above, the malfunction you can learn from this article – rich fuel mixture.

Black smoke from the exhaust pipe in injector engines often appears due to a malfunction of the oxygen sensor, air flow sensor and others. Another frequent malfunction with an enriched mixture is leaky injectors. By the way, if the injectors are not tight, hydrostroke is possible. Leaky injectors are too dangerous thing. Because, even when the engine is not started, a large amount of fuel can leak into the cylinder, and the piston will not be able to rise to the dead center.

Now let’s talk about black smoke from the exhaust of diesel engines. The cause of black smoke can be a malfunction of the high-pressure pump or an incorrect injection advance angle. All engines with enriched mixture are characterized by increased wear of the cylinder piston group. This is due to poor lubrication of the cylinder piston group, because excessive fuel washes oil off the cylinder walls. Also, oil mixed with gasoline impairs lubrication of all other engine parts. Do not delay with repair if you have detected black smoke from the exhaust pipe of the car.