The choice of engine oil, like any other type of oil, depends on two main parameters - viscosity grade and operating class.
Viscosity class for engine oils is determined by the requirements of the standard SAE J300. For an engine, as well as for any other mechanism, it is necessary to use oils with an optimal viscosity, the value of which depends on the design, operating mode, age and ambient temperature.
Operating class determines the quality of engine oil. The development of engine building requires lubricants to meet new, increasingly stringent requirements. To facilitate the selection of oils of the required quality level for a gasoline or diesel engine and their operating conditions, various classification systems have been created. Within each system, motor oils are divided into series and categories based on purpose and quality level.
The following classifications are most widely used:
API– American Petroleum Institute
ILSAC– International Lubricant Standardization and Approval Committee for motor oils.
ACEA– Association of European Automobile Manufacturers (Association des Cunstructeurs Europeens d’Automobiles)
SAE - engine oil viscosity grades
Currently, the only recognized system for classifying motor oils in the world is the specification SAEJ300 . SAE - Society of Automotive Engineers (Society of Automotive Engineers). This classification indicates classes (grades) of viscosity.
The table shows two series of viscosity grades:
Winter- with the letter W (Winter). Oils that meet these categories are low viscosity and are used in winter - SAE 0W, 5W, 10W, 15W, 20W, 25W
Summer- no letters. Oils that meet these categories are high-viscosity and are used in summer - SAE 20, 30, 40, 50, 60.
According to the SAE J300 specification, oil viscosities are determined under conditions close to real. Summer oil has a high viscosity and, accordingly, a high carrying capacity, which provides reliable lubrication at operating temperatures, but it is too viscous at low temperatures, as a result of which the consumer has problems starting the engine. Low-viscosity winter oil facilitates cold start of the engine at low temperatures, but does not provide reliable lubrication in summer. That is why at the moment the most widely used all-weather oils, which are used both in winter and summer.
Such oils are designated by a combination of winter and summer series:
All season oils must meet two criteria at the same time:
Do not exceed low temperature dynamic viscosity ratings (CCS and MRV)
Satisfy the requirements for working kinematic viscosity at 100 ° C
|
Viscosity class |
Dynamic viscosity, mPa-s, |
Kinematic viscosity |
Viscosity HTHS at 150°C and shear rate 106 s-1, mPa-s, not lower |
||
|
cranking (CCS) |
pumpability |
not less |
not higher |
||
|
6200 at - 35°С |
60000 at -40°С |
||||
|
6600 at - 30°C |
60000 at -35°С |
||||
|
7000 at - 25°C |
60000 at - 30°C |
||||
|
7000 at - 20°C |
60000 at -25°C |
||||
|
9500 at - 15°С |
60000 at -20°С |
||||
|
13000 at -10°С |
60000 at -15°С |
||||
* - for viscosity grades 0W-40, 5W-40, 10W-40
** - for viscosity grades 15W-40, 20W-40, 25W-40, 40
Indicators of low temperature properties
crankability(determined on the CCS cold start simulator) - low temperature fluidity criterion. Represents the maximum allowable dynamic viscosity of the engine oil at a cold start, which ensures that the crankshaft cranks at the speed necessary for a successful start of the engine.
Pumpability(determined on an MRV mini-rotational viscometer) - measured 5°C lower to ensure that the oil pump does not suck in air. It is expressed as the value of dynamic viscosity at the temperature of a particular class. Should not exceed a value of 60,000 mPa * s, which ensures pumping through the oil system
High temperature viscosity indexes
Kinematic viscosity at a temperature of 100 ° C. For all-weather oils, this value should be in certain ranges. A decrease in viscosity leads to premature wear of rubbing surfaces - bearings of the crankshaft and camshaft, crank mechanism. An increase in viscosity leads to oil starvation and, as a result, premature wear and engine failure.
Dynamic viscosityHTHS(High Temperature High Shear) - using this test, the stability of the viscosity characteristic of the oil is measured under extreme conditions, at very high temperatures. It is one of the criteria for determining the energy-saving properties of engine oil
Before choosing engine oil, carefully read the operating instructions and manufacturer's recommendations. These recommendations are based on the design features of the engine - the degree of load on the oil, the hydrodynamic resistance of the oil system, the performance of the oil pump.
The manufacturer may allow the use of different viscosity grades of engine oil, depending on the temperature characteristic of your region. The choice of the optimal viscosity of engine oil will ensure consistently reliable operation of your engine.
Currently, there is an abundance of products on the Russian automotive chemicals market. Motor oils, their brands and characteristics are presented in such a rich assortment that they make it difficult for even experienced drivers to choose. One of the main indicators by which you need to choose the right product for your car is the viscosity of engine oil.
What does "viscosity" mean?
There are many different opinions about the viscosity of motor oils - both among professionals and amateurs. Some argue that the degree of viscosity, or fluidity, is an indicator of the thickness of the lubricant, that is, the higher the viscosity, the thicker it is. In fact, viscosity is not so easy to decipher. In order to understand this, you need to get acquainted with the SAE specification. This standard defines the temperature range in which the viscosity qualities of oils for cars correspond to the desired level. These characteristics are measured in the laboratory at certain temperatures.
SAE classification
More than 100 years ago, a community of engineers working in the automotive industry formed in the United States. Already at that time, the problem of good lubricants for cars was acute. The result of collaboration and exchange of ideas was the SAE classifier, which is used today throughout the world.
According toSAE, each automotive lubricant has characteristics such as low temperature and high temperature viscosity.
Today, many amateur motorists claim that there are engine oils that have only low temperature or only high temperature viscosity parameters. They call them, respectively, "winter" and "summer". And if the designation contains both properties of motor oils, separated by the letter W (which, according to them, the word “winter” means), then these are all-weather lubricants. In fact, such an interpretation is incorrect.
It is unlikely that anyone has seen only "summer" or only "winter" motor oil on sale. On store shelves there are all-weather motor fluids that have both viscosity indicators. Let's take a closer look at these values.
Low temperature performance
The viscosity of engine oil at low temperatures is determined by indicators such as "rotation" and "pumpability" of the oil composition. Through laboratory research, it is determined to what minimum temperature it is possible to start the engine painlessly, that is, to crank its crankshaft. A normal start of the car engine is possible only when the lubricant has not yet thickened.
In addition, the lubricant composition must reach the friction pairs in the shortest possible time. This means that at the minimum cranking temperature, the oil must still be fluid enough to move freely through the narrow channels of the system. For example, for 0W30 category oils, the low temperature viscosity level is the first digit (0). For this indicator, the lower limit of pumpability is 40 degrees below zero. At the same time, engine cranking is possible up to -35°C. Accordingly, such engine oil can work well at temperatures down to -35 ° C.
If we take another indicator - 5W20, then here the temperatures will be, respectively, -35 and -30 ° С. That is, the larger the first digit, the smaller the operating range at low temperatures. In the SAE classifier today there are 6 "winter" viscosity categories - 0W, 5W, 10W, 15W, 20W, 25W. These indicators are tied to the ambient temperature, since the temperature of a cold motor depends on it.
High temperature performance
The viscosity of the engine oil over the operating temperature range is not related to the ambient temperature. It is almost the same both at 10 degrees of frost and at 30 degrees of heat. In a car, it is kept stable by the engine cooling system. At the same time, almost every table on the Internet draws different upper limits for ambient temperature for a particular "summer" viscosity. A good example is a comparison of lubricating fluids with indicators 5w30 and 5w20. It is believed that the first of them (5W30) will work well up to an air temperature of + 35 ° C. The second indicator (5W20) is not displayed at all in the tables.
Such a representation is wrong. In addition, the term "summer" viscosity, or "summer" oil, from a professional point of view, is incorrect. This is explained in the video below. The thing is that this parameter is a mode of kinematic and dynamic viscosity, measured at temperatures of +40, +100 and +150°C. Although the operating temperature range in different areas of car engines ranges from +40 to +300 ° C, its average value is taken.
Kinematic viscosity is the fluidity (density) of an oily liquid in the temperature range from +40°C to +100°C. The thinner the lubricant, the lower this indicator, and vice versa. Dynamic viscosity is the resistance force that occurs when two layers of oil, located at a distance of 10 mm from each other, move at a speed of 1 cm / s. The area of each layer is 1 cm2. In other words, tests carried out with the help of special instruments (rotational viscometers) make it possible to simulate the real operating conditions of oils. This indicator does not depend on the density of the engine oil.
Below is a table of viscosity parameters by which one or another of their values is determined.
The table reflects the kinematic and dynamic viscosity technical parameters at certain temperatures (+100 and +150°C), as well as the shear rate gradient. This gradient is the ratio of the speed of movement of the surfaces of the rubbing pair relative to each other to the thickness of the gap between them. The higher this gradient, the more viscous the oil for cars is. In simple terms, the level of viscosity at high temperatures gives information about how thick the oil film is between the gaps and how strong it is. To date, the SAE specification provides for 5 levels of high-temperature viscosity indicators for oils for cars - 20, 30, 40, 50 and 60.
Viscosity index
In addition to the above parameters, viscosity index measurements are also made. He is often overlooked. However, this is the most important parameter.
The viscosity index determines the temperature range in which the viscosity properties remain at a level that ensures normal engine operation. The higher this index, the higher the quality of the lubricant composition.
Regardless of what the SAE value is, whether it is 0W30, 5W20 or 5W30, the oil viscosity index is not tied to it. It directly depends on the composition of the base. For example, for mineral oils it has a value of 85 to 100, for semi-synthetic oils it is 120–140, and for real synthetic compounds this figure reaches 160–180 units. This means that low-viscosity oils such as 5w20 or 5w30 can be used in turbocharged engines with a wide temperature operating range.
In order to increase the viscosity index, so-called binders are often added to the oil mixture. They expand the temperature range in which the oil will retain its basic viscosity qualities. That is, the engine will start well in frosty weather. And at high temperatures, the lubricant composition will create a stable and viscous film in the zone of contact between the surfaces of the parts.
What viscosity is better to choose?
There are many opinions about this, and most of them are erroneous. For example:
For sports models, the requirements are completely different. The main thing there is that the motor withstands the regime of extreme loads and temperatures throughout the race and does not jam from overheating. No one thinks about its long-term use. At critical temperatures, only a viscous oil is able to retain its astringent properties. The other will simply turn into a liquid. Therefore, after each competition, the engines are disassembled and carefully diagnosed. Critical details are immediately changed. Small gaps in friction pairs are out of the question.
How to determine what viscosity is best to use for your car? In the technical documentation for all cars, there are manufacturers' recommendations on what the viscosity values \u200b\u200bof engine oil should be. At the first acquaintance, bewilderment may arise - why, for example, does the manufacturer allow the use of oils with parameters 5w20, 5w30 and 5w40? What is better to fill?
- If the car is still new and has not passed 25% of the declared resource before the first overhaul, low-viscosity lubricants should be used. Like 5W20 or 5W30. By the way, it is low viscosity (5W20) that is recommended for service filling in many brands of Japanese warranty cars.
- If the mileage is between 25 and 75%, formulations with viscosities of 5W should be used. In winter, it is also recommended to use 5W30.
- If the motor is already worn out and has traveled more than 75% of its resource, for such cars it is recommended to use 15W50 in summer, and 5W is suitable in winter
The older the car engine, the more its parts wear out. Accordingly, the gaps between friction pairs increase. Low-viscosity formulations can no longer provide normal lubrication, the oil film breaks. That is why it is recommended to transfer your cars to more viscous motor oils.
Based on the foregoing, choosing the best engine oil for certain car brands is not such an easy task as it seems at first glance. In addition to viscosity indicators, many other quality parameters should be taken into account.
Automobile oil is an indispensable assistant for any motorist. It provides lubrication of mechanisms rubbing together, smoothing surfaces, as well as removing excess debris that occurs when parts interact with each other.
A lot depends on the right choice of lubricants. Firstly, the quality of the selected oils further determines the wear resistance of automotive parts. In addition, the characteristics of the purchased oil determine the ability to function under various temperature conditions. Thirdly, the use of low-quality products entails an increase in the gaps between the interacting mechanisms, which is accompanied by an increase in fuel consumption, wear of expensive parts and mechanisms, and a number of other serious problems.
Viscosity as one of the key parameters of engine oil
The choice of motor oils is determined by various parameters. But for many buyers, the key parameter is the viscosity of the lubricant. Thanks to this parameter, automotive oil lingers longer on the surface of the engine, and is correctly distributed between the rubbing parts.
Basic viscosity parameters
When analyzing the information that manufacturers declare on product labels, each buyer should distinguish between concepts such as kinematic and dynamic viscosity. They differ in density, units and methods of measurement and are used for indicators of different classes of lubricants.
Kinematic viscosity indicates such a property of the oil as its fluidity. It is determined at normal and maximum operating temperatures. Usually, modes such as forty and one hundred degrees Celsius are chosen for testing. This value is measured in centistokes.
Based on the kinematic viscosity, the viscosity index of the engine oil is calculated. If you want to choose the really best lubricant, the index should be more than 200; multigrade oils usually have it.
Dynamic viscosity characterizes the resistance force when liquids move relative to each other, regardless of density. The unit of measure is centipoise.
International standard that regulates the viscosity of oils
To date, the most popular classification of lubricants is SAE. This specification is recognized as the only international standard on the basis of which the viscosity of the oil is calculated based on the temperature regime of the medium.
Society of Automotive Engineers is an acronym for the Society of Automotive Engineers of the United States of America.
The viscosity of the engine oil according to SAE must meet the following conditions:
- pumpability - due to this property, under conditions of minimum temperatures, quick access of oil to the oil receiver is ensured;
- crankability - helps to increase starting properties, provides the necessary resistance and achievement of starting speed in cold weather;
- the most effective viscosity in hot conditions;
- kinematic viscosity - determines the viscosity class of motor oils.
The SAE specification is used when determining the viscosity level of a lubricant, the requirements for oils are taken into account when releasing new products, as well as for research and detailed study of old and new formulations.
Types of oils depending on the temperature regime
The viscosity of lubricants can vary under different conditions. It is directly dependent on the ambient temperature, on the rate of heating of the mechanisms, on the mode of operation of the engine. At low temperatures, the viscosity should not be too high to ensure the vehicle starts in cold weather. In high temperature conditions, on the contrary, the lubricant helps to ensure proper pressure and creates a protective layer between the surfaces that are in contact.
In terms of viscosity, lubricants are divided into winter, summer and all-weather. All-weather products are more convenient. It is more energy efficient, and these oils do not need to be changed as often as materials for a particular season.
Operating temperature ranges for different SAE oils
The table clearly shows at what temperatures different types of lubricants can be used.
The table of viscosity of engine oils by temperature is presented below.
The engine oil viscosity table has numeric and alphanumeric designations, thanks to which the seasonality of the oil and the ambient temperature are determined.
winter oils
As an example, consider the viscosity of 5w30 engine oil. The decoding of the viscosity of engine oil for winter oils is as follows.
For winter oils, an international designation with the letter “w” has been created. When calculating, 40 must be subtracted from the figure in front of it, as a result, we obtain the temperature regime at which lubricant can be used. To find out the cranking temperature of the engine, you need to subtract 35.
Above is a table of engine oil viscosity by temperature. Winter oils are in its upper part.
Winter lubricants are suitable for use under the following temperature conditions:
- 0W - recommended for use in frosts down to -35-30 o C;
- 5W - recommended for use in frosts down to -30-25 o C;
- 10W - recommended for use in frosts down to -25-20 o C;
- 15W - oil is recommended for use in frosts down to -20-15 o C;
- 20W - oil is recommended for use in frosts down to -15-10 o C.
As already mentioned, the viscosity of winter oils must also meet the requirements for crankability, pumpability (should not exceed sixty thousand centipoise) and have the necessary kinetic viscosity.
The table of viscosity of engine oils for cold conditions is presented below.
Summer types of lubricants
Summer production is designated, according to the standard, only with numbers (for example, SAE 30) and means an average parameter indicating the viscosity of the material in working conditions at elevated temperatures.
The motor oil viscosity table for the summer season is as follows.
Multigrade oils
All-weather lubricants are applicable under various thermal conditions. Depending on the season, the viscosity can change and provide proper lubrication of the car's mechanisms. Thus, oils for all seasons meet the criteria for the highest cranking viscosity in cold weather, and the lowest in hot weather.
They are presented at the bottom of the viscosity-by-temperature table and consist of a combination of summer and winter oils.
The decoding is as follows: let's say the viscosity of engine oil is 5W-30: the viscosity grade "5W" allows the use of oil in the cold season, shows how easy it is to start the engine at low temperatures; "30" - indicates the summer class, using this indicator you can calculate the possibility of working at high temperatures.
The choice of engine oil by its viscosity
How to determine the viscosity of engine oil? This may be suggested by the manufacturer's recommendations. The structural features of the engine, its load on lubricants, the level of resistance, the degree of wear of the oil pump, the degree of possible heating of the oil under different operating modes in all places of the motor are taken into account.
When choosing the viscosity of the material for the winter season, you need to take into account the average temperatures of the region of residence. Choosing the right oil will help your car cope with cold starts, which cause additional friction and wear on parts. The engine oil viscosity table will help you navigate the large selection. Manufacturers recommend using SAE 0W among winter oils.
When choosing summer oil, you need to take into account the fact that parts can overheat especially in the hot season, airflow may be insufficient, so the oil must be viscous.
Conclusion
Manufacturers offer a fairly large selection of lubricants. The main characteristic of which is their viscosity. And it, in turn, directly depends on the temperature regime.
Even in very moderate climatic conditions, the temperature difference between the engine and its parts can reach two hundred degrees. The international SAE standard offers a choice of oils for different seasons. Universal oil - all-weather. But as the experience of motorists shows, with too much difference in temperature conditions, great frosts and too hot summers, all-weather lubricants are far from the best.
When choosing a viscosity grade of a lubricant for a personal car, it is necessary to be guided by the following criteria:
- structural features of the car and motor;
- the degree of corrosion of parts, the level of deterioration of the engine;
- basic modes of operation of the motor;
- temperature in different seasons across the region.
Due to such a parameter as viscosity, automobile oil can linger on the surface of the engine longer, be properly distributed between rubbing parts, preventing drying out.
Viscosity is the most important characteristic of engine oil. Below we will describe how motor oils are classified in accordance with GOST and international standards.
Russian GOST 17479.1 divides oils depending on the kinematic viscosity at different temperatures into the following viscosity classes: summer oils
- 8*, 10, 12, 14, 16, 20, 24 winter oils
- Zz, 4z, 5z, 6z, 6, 8* all season oils
- are indicated by a fractional index (for example, 5z / 12, 6z / 14, etc.)
For all grades, kinematic viscosity limits are normalized at 100°С, and for winter and all-weather grades, kinematic viscosity is additionally normalized at –18°С** (Table 1).
| Viscosity class according to GOST 17479.1 | Kinematic viscosity, mm2/s, at + 100°C | Viscosity kinematic, mm2/s, at temperature – 18°С | |
|---|---|---|---|
| at least | no more | no more | |
| Zz | 3,8 | – | 1250 |
| 4h | 4,1 | – | 2600 |
| 5z | 5,6 | – | 6000 |
| 6z | 5,6 | – | 10 400 |
| 6 | 5,6 | 7,0 | – |
| 8 | 7,0 | 9,3 | – |
| 10 | 9,3 | 11,5 | – |
| 12 | 11,5 | 12,5 | – |
| 14 | 12,5 | 14,5 | – |
| 16 | 14,5 | 16,3 | – |
| 20 | 16,3 | 21,9 | – |
| 24 | 21,9 | 26,1 | – |
| 33/8 | 7,0 | 9,5 | 1250 |
| 4z/6 | 5,6 | 7,0 | 2600 |
| 4z/8 | 7,0 | 9,3 | 2600 |
| 4g/10 | 9,3 | 11,5 | 2600 |
| 5g/10 | 9,3 | 11,5 | 6000 |
| 5z/12 | 11,5 | 12,5 | 6000 |
| 5z/14 | 12,5 | 14,5 | 6000 |
| 6z/10 | 9,3 | 11,5 | 10 400 |
| 6z/12 | 11,5 | 12,5 | 10 400 |
| 6z/14 | 12,5 | 14,5 | 10 400 |
| 6z/16 | 14,5 | 16,3 | 10 400 |
For all-weather oils, the figure in the numerator characterizes the winter class, and in the denominator - summer; the letter "z" indicates that the oil is thickened, i.e. contains a thickening (viscosity) additive. Thus, all-weather oil of viscosity class 5z/12 in terms of kinematic viscosity at 100°C corresponds to summer oil of class 12, and at –18°C - to winter oil of class 5z.
Class 8 oil is often used both in summer and in winter.
According to GOST 51634-2000, instead of kinematic viscosity at minus 18, it is allowed to normalize the apparent (dynamic) viscosity at low temperatures.
In most developed countries of the world, the viscosity classification of motor oils established by the SAE (American Society of Automotive Engineers) in the SAE J-300 DEC 99 standard and put into effect since August 2001 (Table 2) is generally accepted.
This classification contains 11 classes: 6 winter
- 0w, 5w, 10w, 15w, 20w, 25w (w-winter, winter) 5 summer
- 20, 30, 40, 50, 60.
All-weather oils have a double hyphen designation, with the winter (with index w) class being the first, and the summer class being the second, for example SAE 5w-40, SAE 10w-30, etc. Winter oils characterize two maximum values of dynamic (as opposed to kinematic for GOST) viscosity and a lower limit of kinematic viscosity at 100°C. Summer oils characterize the limits of kinematic viscosity at 100°C, as well as the minimum value of dynamic high-temperature (at 150°C) viscosity at a shear rate gradient of 10E6s-1.
In both viscosity classifications (GOST, SAE), the smaller the number in the numerator with the index “z” (GOST) or before the letter “w” (SAE), the lower the viscosity of the oil at low temperatures and, accordingly, the easier the cold start of the engine. The larger the number in the denominator (GOST) or after the hyphen (SAE), the greater the viscosity of the oil at high temperatures and the more reliable engine lubrication in the summer heat.
Table 3 shows an approximate correspondence between the viscosity grades of motor oils according to GOST 17479.1-85 and the viscosity grades according to SAE J-300.
| Viscosity class | Low temperature (dynamic) viscosity | High temperature viscosity | High temperature viscosity | High temperature viscosity | |
|---|---|---|---|---|---|
| turning | pumpability | kinematic at 100°С | kinematic at 100°С | dynamic at 150°С and shear rate 10E6 s-1 | |
| according to ASTM D 5293 (CCS viscometer, cold start simulation), mPa s | according to ASTM D 4684 (MRV viscometer) kinematic at 100°С, mPa s | (by ASTM D 445 method), mm2/s | according to ASTM D 4683 or CEC L-36-A-90, on a tapered bearing simulator, mPa s | ||
| maximum viscosity, at temperature | min | max | min | ||
| 0w | 6200 at -35°С | 60,000 at -40°C | 3,8 | - | - |
| 5w | 6600 at -30°С | 60,000 at -35°С | 3,8 | - | - |
| 10w | 7000 at -25°С | 60,000 at -30°C | 4,1 | - | - |
| 15w | 7000 at -20°С | 60,000 at -25°C | 5,6 | - | - |
| 20w | 9500 at -15°C | 60,000 at -20°C | 5,6 | - | - |
| 25w | 13,000 at -10°C | 60,000 at -15°C | 9,3 | - | - |
| 20 | - | - | 5,6 | 9,3 | 2,6 |
| 30 | - | - | 9,3 | 12,5 | 2,9 |
| 40 | - | - | 12,5 | 16,3 | 2,9* |
| 40 | - | - | 12,5 | 16,3 | 3,7** |
| 50 | - | - | 16,3 | 21,9 | 3,7 |
| 60 | - | - | 21,9 | 26,1 | 3,7 |
* For SAE grades 0w-40, 5w-40, 10w-40.
** For SAE 40, 15w-40, 20w-40, 25w-40 grades.
Approximate ratio of viscosity grades of motor oils according to GOST 17479.1-85 to viscosity grades according to SAE J-300
| Viscosity grade according to SAE J-300 | Viscosity class according to GOST 17479.1-85 | Viscosity grade no SAE J-300 | |
|---|---|---|---|
| Zz | 5w | 24 | 60 |
| 4h | 10w | 33/8 | 5w-20 |
| 5z | 15w | 4z/6 | 10w-20 |
| 6z | 20w | 4z/8 | |
| 6 | 20 | 4g/10 | 10w-30 |
| 8 | 5g/10 | 15w-30 | |
| 10 | 30 | 5z/12 | |
| 12 | 5z/14 | 15w-40 | |
| 14 | 40 | 6z/12 | 20w-30 |
| 16 | 6z/14 | 20w-40 | |
| 20 | 50 | 6z/16 |
The choice of engine oil is a serious task for every motorist. And the main parameter by which the selection should be carried out is the viscosity of the oil. The viscosity of the oil characterizes the degree of density of the motor fluid and its ability to maintain its properties during temperature changes.
Let's try to figure out in what units viscosity should be measured, what functions it performs and why it plays a huge role in the operation of the entire propulsion system.
The operation of an internal combustion engine involves the continuous interaction of its structural elements. Imagine for a second that the motor is running dry. What will happen to him? First, the force of friction will increase the temperature inside the device. Secondly, deformation and wear of parts will occur. And, finally, all this will lead to a complete stop of the internal combustion engine and the impossibility of its further use. Properly selected engine oil performs the following functions:
- protects the motor from overheating
- prevents rapid wear of mechanisms,
- prevents the formation of corrosion,
- removes carbon deposits, soot and fuel combustion products outside the engine system,
- helps to increase the resource of the power unit.
Thus, the normal functioning of the motor department without a lubricant is impossible.
Important! It is only necessary to fill in the vehicle engine with oil whose viscosity meets the requirements of automakers. In this case, the efficiency will be maximum, and the wear of the working units will be minimal. It is not worth trusting the opinions of sales consultants, friends and car service specialists if they disagree with the instructions for the car. After all, only the manufacturer can know for sure what it is worth refueling the engine.
Oil viscosity index
The concept of viscosity of oils refers to the ability of a liquid to be viscous. It is determined using the viscosity index. The viscosity index of an oil is a value that shows the degree of viscosity of an oily fluid with temperature changes. Lubricants with a high degree of viscosity have the following properties:
- when starting the engine cold, the protective film has a strong fluidity, which ensures quick and even distribution of lubricant over the entire working surface;
- engine heating causes an increase in film viscosity. This property allows you to keep the protective film on the surfaces of moving parts.
Those. oils with a high viscosity index easily adapt to thermal overload, while a low viscosity index of an engine oil indicates less ability. Such substances have a more liquid state and form a thin protective film on the parts. Under conditions of negative temperatures, a motor fluid with a low viscosity index will make it difficult to start the power unit, and in high temperature conditions it will not be able to prevent a large friction force.
The calculation of the viscosity index is carried out in accordance with GOST 25371-82. You can calculate it using online services on the Internet.
Kinematic and dynamic viscosity
The degree of ductility of the motor material is determined by two indicators - kinematic and dynamic viscosities.
Engine oil
The kinematic viscosity of an oil is an indicator that reflects its fluidity at normal (+40 degrees Celsius) and high (+100 degrees Celsius) temperatures. The technique for measuring this value is based on the use of a capillary viscometer. The instrument measures the time required for the oil to flow out at given temperatures. The kinematic viscosity is measured in mm 2 /s.
The dynamic viscosity of the oil is also calculated empirically. It shows the resistance force of an oily liquid that occurs during the movement of two layers of oil, separated from each other at a distance of 1 centimeter and moving at a speed of 1 cm / s. The units of this value are Pascal seconds.
The determination of the viscosity of the oil must take place under different temperature conditions, because the liquid is not stable and changes its properties at low and high temperatures.
The table of viscosity of engine oils by temperature is presented below.
Deciphering the designation of engine oil
As noted earlier, viscosity is the main parameter of a protective fluid that characterizes its ability to ensure vehicle performance in various climatic conditions.
According to the international SAE classification system, motor lubricants can be of three types: winter, summer and all-weather.
Oil intended for winter use is marked with a number and the letter W, for example, 5W, 10W, 15W. The first symbol of the marking indicates the range of negative operating temperatures. The letter W - from the English word "Winter" - winter - informs the buyer about the possibility of using the lubricant in harsh low-temperature conditions. It has a greater fluidity than the summer counterpart in order to provide easy starting at low temperatures. The liquid film instantly envelops cold elements and makes them easier to scroll.
The limit of negative temperatures at which the oil remains operational is as follows: for 0W - (-40) degrees Celsius, for 5W - (-35) degrees, for 10W - (-25) degrees, for 15W - (-35) degrees.
Summer liquid has a high viscosity, which allows the film to “hold” on the working elements more firmly. At too high temperatures, such oil spreads evenly over the working surface of the parts and protects them from heavy wear. Such oil is indicated by numbers, for example, 20,30,40, etc. This figure characterizes the high-temperature limit in which the liquid retains its properties.
Important! What do the numbers mean? The figures for the summer parameter in no way indicate the maximum temperature at which the vehicle can operate. They are conditional and have nothing to do with the degree scale.
Oil with a viscosity of 30 functions normally at ambient temperatures up to +30 degrees Celsius, 40 - up to +45 degrees, 50 - up to +50 degrees.
Recognizing universal oil is simple: its marking includes two numbers and the letter W between them, for example, 5w30. Its use implies any climatic conditions, whether it be harsh winters or hot summers. In both cases, the oil will adapt to changes and keep the entire engine system working.
By the way, the climatic range of universal oil is determined simply. For example, for 5W30 it varies from minus 35 to +30 degrees Celsius.
All-weather oils are easy to use, so they are more common on the shelves of car dealerships than summer and winter options.
In order to have a better idea of what viscosity of engine oil is appropriate in your area, below is a table showing the operating temperature range for each type of lubricant.
Average oil performance ranges
Having figured out what the numbers in the viscosity of the oil mean, let's move on to the next standard. The classification of engine oil by viscosity also affects the API standard. Depending on the type of engine, the API designation begins with the letter S or C. S means gasoline engines, C - diesel. The second letter of the classification indicates the quality class of the engine oil. And the further this letter is from the beginning of the alphabet, the better the quality of the protective liquid.
For gasoline propulsion systems, the following designations exist:
- SC - year before 1964
- SD - year of manufacture from 1964 to 1968.
- SE - year of manufacture from 1969 to 1972.
- SF - year of manufacture from 1973 to 1988.
- SG - year of manufacture from 1989 to 1994.
- SH - year of manufacture from 1995 to 1996.
- SJ - year of issue from 1997 to 2000.
- SL - year of manufacture from 2001 to 2003.
- SM - year of manufacture after 2004.
- SN - cars equipped with a modern exhaust gas aftertreatment system.
For diesel:
- CB - the year of issue before 1961.
- CC - year of manufacture before 1983.
- CD - year before 1990
- CE - year of manufacture up to 1990, (turbocharged engine).
- CF - year of manufacture since 1990, (turbocharged engine).
- CG-4 - year of manufacture since 1994, (turbocharged engine).
- CH-4 - year of manufacture since 1998
- CI-4 - modern cars (turbo engine).
- CI-4 plus - a much higher class.
What's good for one engine is bad for another
Engine oil
Many car owners are sure that it is worth choosing more viscous oils, because they are the key to long-term engine operation. This is a serious misconception. Yes, specialists pour oil with a high degree of viscosity under the hoods of racing cars to achieve the maximum resource of the power unit. But ordinary passenger cars are equipped with a different system, which will simply choke if the protective film is too thick.
About what viscosity of oil it is permissible to use in the engine of a particular machine, it is described in any instruction manual.
Indeed, before the launch of mass sales of models, automakers conducted a large number of tests, taking into account the possible driving modes and operation of the technical tool in various climatic conditions. By analyzing the behavior of the motor and its ability to maintain stable operation in certain conditions, the engineers set the acceptable parameters for motor lubrication. Deviation from them can cause a decrease in the power of the propulsion system, its overheating, an increase in fuel consumption, and much more.
Engine oil in the engine
Why is the viscosity class so important in the operation of mechanisms? Imagine for a moment the engine from the inside: there is a gap between the cylinders and the piston, the size of which should allow for the possible expansion of parts from high-temperature drops. But for maximum efficiency, this gap should have a minimum value, preventing exhaust gases generated during the combustion of the fuel mixture from entering the engine system. In order for the piston body not to heat up from contact with the cylinders, motor lubricant is used.
The viscosity level of the oil must ensure the performance of each element of the propulsion system. Manufacturers of power units must achieve the optimal ratio of the minimum clearance between the rubbing parts and the oil film, preventing premature wear of the elements and increasing the engine's working life. Agree, it is safer to trust official representatives of a car brand, knowing how this knowledge was obtained, than to trust "experienced" motorists who rely on intuition.
What happens when the engine is started?
If your “iron friend” stood all night in the cold, then in the morning the viscosity of the oil poured into it will be several times higher than the calculated working value. Accordingly, the thickness of the protective film will exceed the gaps between the elements. At the time of starting a cold engine, its power drops and the temperature inside it rises. Thus, the motor warms up.
Important! During warm-up, you can not give him an increased load. Too thick a lubricant composition will impede the movement of the main mechanisms and lead to a reduction in the life of the vehicle.
Engine oil viscosity at operating temperatures
After the engine has warmed up, the cooling system is activated. One engine cycle looks like this:
- Pressing the gas pedal increases the engine speed and increases the load on it, as a result of which the friction force of the parts increases (since too astringent liquid has not yet had time to get into the inter-part gaps),
- oil temperature rises
- the degree of its viscosity decreases (fluidity increases),
- the thickness of the oil layer decreases (leaks into the inter-part gaps),
- friction force is reduced
- the temperature of the oil film is reduced (partially by the cooling system).
This principle works in any propulsion system.
The viscosity of motor oils at a temperature of - 20 degrees
The dependence of oil viscosity on operating temperature is obvious. Just as it is obvious that the high level of motor protection should not be reduced during the entire period of operation. The slightest deviation from the norm can lead to the disappearance of the motor film, which in turn will negatively affect the “defenseless” part.
Each internal combustion engine, although it has a similar design, has a unique set of consumer properties: power, efficiency, environmental friendliness and torque. These differences are explained by the difference in engine clearances and operating temperatures.
In order to select the oil for the vehicle as accurately as possible, international classifications of motor fluids have been developed.
The classification provided by the SAE standard informs car owners about the average operating temperature range. API, ACEA, etc. classifications give a clearer idea of \u200b\u200bthe possibility of using a lubricant in certain vehicles.
Consequences of filling oil with increased viscosity
There are times when car owners do not know how to determine the required viscosity of engine oil for their car, and fill in the one recommended by the sellers. What happens if the ductility is higher than required?
If in a well-heated engine oil with high viscosity “splashes”, then there is no danger for the engine (at normal speeds). In this case, the temperature inside the unit will simply increase, which will lead to a decrease in the viscosity of the lubricant. Those. the situation will return to normal. But! Regular repetition of this scheme will significantly reduce motor resources.
If you suddenly “give gas”, causing an increase in speed, the degree of viscosity of the liquid will not correspond to the temperature. This will cause the maximum allowable temperature in the engine compartment to be exceeded. Overheating will cause an increase in friction force and a decrease in wear resistance of parts. By the way, the oil itself will also lose its properties in a fairly short period of time.
You will not be able to instantly find out that the viscosity of the oil did not fit the vehicle.
The first "symptoms" will appear only after 100-150 thousand kilometers. And the main indicator will be an increase in the gaps between the parts. However, even experienced specialists will not be able to definitely connect the high viscosity and the rapid decrease in the motor resource. It is for this reason that official auto repair shops often neglect the requirements of vehicle manufacturers. In addition, it is beneficial for them to repair the power units of cars that have already expired warranty service. That is why the choice of oil viscosity is a difficult task for every motorist.
Too low viscosity: is it dangerous?
Engine oil
Low viscosity can kill gasoline and diesel engines. This fact is explained by the fact that at elevated operating temperatures and loads on the motor, the fluidity of the enveloping film increases, as a result of which the already liquid protection simply “exposes” the details. Result: increase in friction force, increase in fuel consumption, deformation of mechanisms. Long-term operation of a car filled with a low-viscosity liquid is impossible - it will jam almost immediately.
Some modern engine models involve the use of so-called "energy-saving" oils with a reduced viscosity. But they can only be used if there are special approvals from car manufacturers: ACEA A1, B1 and ACEA A5, B5.
Oil Thickness Stabilizers
Due to constant temperature overloads, the viscosity of the oil gradually begins to decrease. And special stabilizers can help restore it. They can be used in engines of any type, the wear of which has reached an average or high level.
Stabilizers allow:
Stabilizers
- increase the viscosity of the protective film,
- reduce the amount of carbon deposits and deposits on the engine cylinders,
- reduce the emission of harmful substances into the atmosphere,
- restore the protective oil layer,
- to achieve "noiselessness" in the operation of the engine,
- prevent oxidation processes inside the motor housing.
The use of stabilizers allows not only to increase the period between "oil" changes, but also to restore the lost useful properties of the protective layer.
Varieties of special lubricants used in production
Spindle type lubricant has low viscosity properties. The use of such protection is rational on motors with a low load and operating at high speeds. Most often, such a lubricant is used in textile production.
Turbine lubricant. Its main feature is to protect all working mechanisms from oxidation and premature wear. The optimum viscosity of turbine oil allows it to be used in turbocharger drives, gas, steam and hydraulic turbines.
VMGZ or all-season hydraulic thickened oil. Such a liquid is ideal for equipment used in Siberia, the Far North and the Far East. This oil is intended for internal combustion engines equipped with hydraulic drives. VMGZ is not divided into summer and winter oils, because its use implies only a low-temperature climate.
The raw materials for hydraulic oil are low-viscosity components containing a mineral base. In order for the oil to reach the desired consistency, special additives are added to it.
The viscosity of the hydraulic oil is shown in the table below.
OilRight is another lubricant used for the conservation and processing of mechanisms. It has a waterproof graphite base and retains its properties in the temperature range from minus 20 degrees Celsius to plus 70 degrees Celsius.
conclusions
An unequivocal answer to the question: “what is the best viscosity of engine oil?” no and cannot be. The thing is that the required degree of ductility for each mechanism - whether it be a loom or a racing car engine - has its own, and it is impossible to determine it “at random”. The required parameters of lubricating fluids are calculated by manufacturers empirically, therefore, when choosing a fluid for your vehicle, first of all, follow the instructions of the developer. And after that, you can refer to the engine oil viscosity table by temperature.
