Marking and classification of motor oils by viscosity using the SAE system

The physical concept of motor oil viscosity is interpreted as the ability to resist the movement of one part of a substance relative to another. This is the friction of layers against each other within a liquid. The less mobile the liquid, the greater its viscosity. It depends: on the type of substance, impurities, additives (additives are used for this), the temperature of the liquid itself.

It is important for a motorist to consider and know:

• what lubricant is better to choose for the engine;
• how to understand the inscriptions on the label;
• what does the engine oil marking mean, what is its meaning;
• how the wrong choice of car oil will affect engine performance;
• What does SAE standard mean?

SAE oil classification

Society of Automotive Engineers (SAE) - the society of automotive engineers has created its own viscosity marking, which is used almost all over the globe and is similar to the Russian classification.

The division according to this classifier looks like this:

• all-season - universal compositions that adapt to the external temperature;
• summer - work flawlessly at readings above 0C;
• winter ones are designated as W - they guarantee a cold start at any temperature not exceeding 0C.

These oils are divided into ten classes, according to their viscosity values ​​and temperature limits. The marking of winter products consists of a letter and a number, which indicates the operating temperature. The smaller it is, the lower the number indicated on the label. The range is most often represented by 20W, 15W, 10W,5W, 0W.

Summer MMs do not have letters in their designation; only their temperature limit is indicated - from 20 to 50 (with an interval of 10 units). Accordingly, a high digital indicator indicates a high temperature at which it stores its characteristics without losing its beneficial properties.

All-season compositions are marked with a hyphen and contain the indicators of the two previous classes. The greater the difference between these numbers, the greater the operating limits.

Winter MM according to SAE have a range from 0W to 25W with an interval of 5 units. 5W can be used in the most severe frosts, and 10 W guarantees engine starting at a temperature not lower than -30 and can be used in moderate climates. If the car is equipped with a powerful starter and has a reliable battery, then using 15W at a temperature of -25 degrees is acceptable. An ideal product for any season in temperate climates. In rallies and auto racing, W20 is most often used with a temperature rating of at least -20 degrees.

Summer MMs have 5 names: SAE60, 50, 40, 30, 20. All-season ones, respectively, have the designations SAE10W-40, 15W-30, 20W-20, 5w40.

Classification of automobile oils according to the SAE system

The author's classification of motor oils according to SAE belongs to the American Association of Automotive Engineers. The system, in its first edition, was introduced in 1911. Classification according to the SAE system is based on viscosity characteristics depending on ambient temperatures, conditions under which the engine will be operated safely and optimally.

To consider what oil viscosity is, what is the detailed breakdown of indicators according to the SAE system, let’s introduce the concepts of kinematic and dynamic viscosity in motor oil.

With increasing temperature, the viscosity of any liquid begins to decrease, as the mutual attraction of molecules decreases. This process is characterized by the kinematic viscosity of any motor oil. In this regard, another value characterizing the properties of oils is introduced, the viscosity index, which shows the rate of decrease in the thickness of the engine oil per unit of time.

The second characteristic, the dynamic viscosity of engine oil, shows how much force must be applied to move a portion of a substance, relative to the area of ​​​​shear.

These two characteristics are very important! A chain of reasoning can be given when using a lubricant with an insufficient viscosity index in an engine.

1. As the temperature rises, the viscosity quickly decreases (low oil viscosity index according to SAE).
2. The lubricant covers the engine components with a very thin film.
3. Friction between parts in contact increases.
4. The result is engine failure.

Or another option:

1. Dynamic viscosity is not sufficient.
2. The starter cannot crank the engine.
3. The lubricant does not reach all components.
4. The engine starts dry.
5. Lots of friction.
6. The engine is jamming.

The index is often not printed on labels. It can only be obtained from the seller. The usual boundaries are:

• Mineral IV – 120-140;
• Synthetic IV – 140-170;
• IV semi-synthetics – 130-150.

Oil with a high Viscosity Index (VI) remains quite liquid at low subzero temperatures, and at high positive temperatures and a well-heated engine, it remains quite thick. This ensures its excellent functioning.

It is important to know the correct engine oil for a given engine. Use the optimal option recommended by the SAE system. The right choice depends on:

• motor operating power;
• ease and speed of starting a cold engine;
• Engine efficiency;
• the amount of oxide flakes formed during fuel combustion;
• fuel consumption;
• oil consumption and timing.

The classification of motor oils involves division into three groups according to the ambient temperature in which the engine starts: summer, winter and all-season. At these temperatures, the viscosity of motor oils is optimal; the table below shows their application limits.

The greater the difference between the maximum and minimum temperatures in the cold and warm seasons, the higher the viscosity index should be. Having such characteristics, the oil is considered high quality.

API classification

The API (American Petroleum Institute) classification is also popular. She takes the ratio of motor conditions and MM properties as a criterion for separating. The marking uses two symbols. The first speaks about the type of engine (C - diesel, S - gasoline), and the second (from A to H inclusive) speaks about the operating properties of the composition.

A special feature is that the load increases as the letter moves away from the beginning of the alphabet. For example, SA and CA products are good for unboosted power plants, while highly boosted, multi-valve engines and turbocharged units use SH and CD.

Manufacturers focus on both classifications. At the moment, preference is given to all-season compositions. As a rule, products suitable for both diesel and gasoline engines are used in production.

According to this classifier, MMs have four main indicators: the type of internal combustion engine and its operating mode, year of production, operating conditions and features. As a result, there is a division into 2 classes:

• Service “S” - compounds for four-stroke gasoline units;
• Commercial "C" - products for diesel installations in automobile, agricultural and construction vehicles.

The marking is a combination of two letters:

• S/C comes first;
• Operation level – A, B, C, D, E, F, G, H, J, L, M, N.

Category C	Category S
CH-4 – used on high-speed diesel engines	SH – gasoline engines of passenger cars, small trucks and vans.	SJ - repeats the properties of SH and has additional advantages - more economical fuel consumption, increased energy saving, control of deposits
CJ-4 – are used on high-speed diesel engines, have additional criteria for durability, preventing the accumulation of deposits and foaming, and antioxidant effect	SM is essentially a tougher variation of SL	SL – requires increased antioxidant, cleansing and energy-saving qualities
CI-4 - high-speed diesel engines. Compatible with particulate filtration and emission control devices, with improved properties of CJ-4	SN - introduces additional requirements for energy saving and durability. Assumes an increase in resource. Used on engines using biofuels.

Types of fluids

Consumables for gasoline and diesel engines may have different compositions, as well as approvals for use in certain vehicles. In terms of its structure, any oil, be it synthetic, semi-synthetic or mineral, has a chemically complex composition. The basis of any fluid for gasoline and diesel engines is the lubricant itself, as well as various additives necessary to ensure certain characteristics. Today there are three types of lubricants:

• Mineral lubricants have high viscosity characteristics. Essentially, mineral oils are a natural substance obtained from the refining of petroleum products. According to the parameters and main characteristics, such lubricants usually have a short service life, and due to the fact that the liquid evaporates, during operation its consumption is significantly higher than that of other lubricants. Experts recommend using such MMs in old engines whose service life is already more than fifteen years.
• Synthetic oil is a lubricant with low viscosity characteristics. Synthetics are made through the process of synthesizing chemical elements and processing them. Thus, synthetic manufacturers manage to achieve better performance characteristics and their overall values. Synthetics make it possible to more reliably protect the engine, including when operating in difficult conditions at low temperatures. The lubricant almost does not evaporate; due to its composition, it is more resistant to various types of oxidation processes. It should also be added that synthetics have a longer service life. However, compared to mineral lubricants, synthetic lubricants have lower characteristics, so more additives are added to them.
• Semi-synthetics are essentially a mixture of synthetic and mineral lubricants. Usually the ratio of synthetics and mineral water is about 30-50%! to 70-50%! The purpose of semi-synthetics is usually for use in cars with high mileage.

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Consumables for gasoline and diesel engines may have different compositions

Today, when producing vehicles, most automakers have specific requirements for consumables so that the driver clearly understands what fluid can be used in the engine. Motor oil viscosity is one of the main indicators that consumers pay attention to. As the operating temperature of the engine decreases, the viscosity of the engine oil increases, and as the temperature increases, this value decreases accordingly. This applies to both diesel and gasoline engines.

If the viscosity value is too high and the temperature of the gasoline or diesel engine is too low, the result may be that the starter will not be able to crank the crankshaft. Accordingly, it will not be possible to start the internal combustion engine.

ILSAC

Together with the API, the MM marking according to the ILSAC classifier is often used. The main distinctive features of the MM are:

• low phosphorus content;
• reduced viscosity;
• fuel economy and energy saving;
• filtration at low temperatures;
• low volatility;
• reduced level of foaming.

There are 5 main classes according to ILSAC: GF-1 – GF-5. GF-5 is designed for increased protection of piston and turbo compressors from various precipitation, characterized by interaction with sealing components and increases the service life of internal combustion engines operating on bio-class fuel containing ethanol.

GF-4 have increased fuel efficiency, longer oil service life before replacement, composition resistance to operational loads, protection of systems to reduce toxins in the exhaust. GF-3 is close in quality requirements to GF-4. Their main difference is enhanced control over the additives contained and their stability, compliance with lubricant consumption during operation.

Class GF-2 has one of the main requirements - the phosphorus content in the volume is no more than 0.1%. Also, MMs must operate at low temperatures and be resistant to foaming and temperature deposits. These criteria include OW-30, OW-40, 10W-40, 10W-30, 5W-50, 5W-40, 5W-30 and 5W-20.

GF-1 is the most loyal and has minimal requirements for MM. Among them: economical fuel consumption, reduced toxin content, economical fuel consumption and the proportion of phosphorus no more than 0.12%.

Main parameters characterizing low-temperature properties according to SAE

The crankability index determines the fluidity parameters of the oil at low temperatures. This parameter should be understood as the maximum permissible level of oil viscosity when starting an engine operating under low temperature conditions. The crankability must allow the crankshaft to turn at such a speed that the engine can start.

The pumpability index is expressed by the value of the dynamic viscosity index for the temperature regime of each specific class. This parameter should not exceed 60,000 mPa*s, but at the same time it should ensure pumping through the oil circulation system. Measured with a mini rotational viscometer MRV. In practice, it is measured at a temperature 5ºС less than the calculated one, while the engine should not suck in air from the external environment.

High temperature viscosity is characterized by the following indicators

The kinematic viscosity indicator is measured at a temperature of 100ºC. This parameter, for all-season oil, should not go beyond the established range. Since when the viscosity decreases, premature wear of rubbing surfaces, such as the bearing, crankshaft, camshaft, and crank mechanism, will occur. And if the upper limit is exceeded, it causes oil starvation and also premature wear and failure of the mechanical part of the engine.

Comparison of oils at a temperature of -35

Dynamic viscosity index HTHS

Shows how stable the viscosity characteristics of the lubricant are when operating under extreme operating conditions (high temperature mode). It is one of the main parameters characterizing the energy-saving properties of motor oils.

Depending on the type of materials, all engine oils are divided into three main types of classification:

1. Mineral-based lubricants obtained by distilling waste petroleum products or from agricultural crops. This category is characterized by rapid evaporation and low resistance to chemical processes and low resistance to various influences. The viscosity index in mineral oils is quite high. But such oils will be quickly consumed.
2. Synthetic based lubricants. For such oils, the main feature is a low degree of viscosity. The manufacturing technology is based on oil refining and subsequent chemical processing. Such oils are much less susceptible to aggressive environments, they are more stable and provide reliable protection of engine parts.
3. Semi-synthetic lubricants consist of a mixture of mineral and synthetic oils and are prominent representatives of all-season machine lubricants.

ACEA classifier

In essence, it is the European analogue of the API. Its peculiarity is mandatory testing of products for compliance with the standard. For these purposes, there is the EELQMS Corporation, which conducts testing and issues certificates of successful completion.

According to this classifier, MMs are divided into three categories:

1. A/B compositions for installations running on both diesel and gasoline;
2. C products that are distinguished by the strict requirements for environmental friendliness of exhaust gases Euro-4. They function perfectly in conjunction with catalysts and particulate filtration;
3. E - diesel internal combustion engines of heavy and freight transport.

For clarity, it is better to present the classification in the form of a table.

MM according to ACEA	Properties
A1	Lowest possible viscosity level. Economical fuel consumption at large shear and high temperatures. Use only as recommended by car manufacturers.
A2	Normal operating conditions for gasoline units with the usual replacement frequency.
A3	High performance. Act as all-season compositions with a low level of stable viscosity. Allows you to increase the frequency of replacement.
IN 1	Almost identical to A1, they are used at the insistence of internal combustion engine manufacturers due to their individual characteristics.
AT 2	Working option for diesel units with intermediate injection design. Replacement frequency is within normal limits.
AT 3	Used on diesel engines with intermediate injection and a longer replacement interval. They are characterized by low viscosity and all-season qualities.
AT 4	Used in case of factory recommendations on diesel engines with a direct injection system.
E1	They are used in naturally aspirated diesel engines or turbo engines for medium or light duty operation. The replacement interval is within normal limits.
E2	Medium and complex operation of turbo engines or naturally aspirated diesel engines. Regular replacement.
E3	Provides ideal cleanliness and a mirror-like film of the piston, reducing wear and preventing the formation of deposits. Most often used on Euro-1 and 2 engines.
E4	MM with properties exceeding the requirements of the previous class. Suitable for Euro-1 and 2 high-speed vehicles in the most difficult working conditions.

Seasonal classification of motor oils and their brief characteristics

Dependence of oil viscosity on temperature
Almost every type of lubricant has its own temperature range for use in a power plant. All of them are divided into the following large groups.

1. Winter types (examples - 5W30, 0W40 oils). This group is characterized by a relatively low degree of viscosity. Due to this quality, the materials of this group ensure normal engine starting at low temperatures. But special winter oils cannot guarantee complete engine lubrication in hot summer conditions.
2. Summer views. They are actually the complete opposite of winter lubricants. Their structure makes it possible to provide the power plant with reliable lubrication in conditions of high summer temperatures. At the same time, oils belonging to this group do not tolerate atmospheric temperatures below 0 ° C and do not guarantee normal cold starting of the engine.
3. All-season types (example - 5W40 and 10W 40 oils). Their peculiarity is that in conditions of high temperatures they behave like summer species, and in conditions of negative temperatures - like winter species.

In order to achieve the desired seasonal characteristics in all-season species, special additives are used in the production of these materials. Their task is to slow down liquefaction at summer temperatures and thickening at winter temperatures. Due to their universal qualities and ease of use (in particular, there is no need for frequent replacement of lubricants when moving from one season to another), all-season types have gained great popularity among motorists and are now actively replacing winter and summer options.

Classification by composition

The easiest and most understandable is to define a class based on MM. So they are divided into:

• synthetic;
• mineral;
• semi-synthetic.

This division characterizes not only the contents of the product, but also the viscosity, temperature resistance, and the resulting use and cost. This classification also allows us to pay due attention to the various additives used in production. They serve to improve and enhance the main characteristics of MM and have a significant impact on the cost of products.

SAE - viscosity grades of transmission oils

Viscosity grade	Max. pace. at which the viscosity does not exceed 150000 cP, 0С	Kinematic viscosity at 1000C, cST
		minimum	maximum
70W	-55	4,1	—
75W	-40	4,1	—
80W	-26	7,0	—
85W	-12	11,0	—
90	—	13,5	24,0
140	—	24,0	41,0
250	—	41,0	—

How to choose motor oil?

• In order not to throw money away, first of all, you need to rely on the recommendations of technical documents of a specific car model.
• The temperature range given by the MM manufacturer cannot be a reliable reason for purchase.
• Additives make the color of the product darker, so trying to choose a product by color is a hopeless endeavor.
• You should not mix different brands of MM.
• You cannot use oils with different bases at the same time (mineral in tandem with synthetics will ultimately produce flakes that will clog the channels).
• First of all, you need to focus not on the manufacturer, but on the compliance of the product properties with the engine requirements.

Examples of designations on motor oil labels

Lubricants for automobile engines are designated by alphanumeric indices, which fairly fully display the information necessary for the optimal selection of oils for a certain type of engine and its operating conditions. These indices have their own clear and regular structure, which can be examined using some specific examples.

Most often on the labels of modern motor oils there is a designation consisting of two numbers separated by the English letter “W” (from the word winter). Let's take the all-season product SAE 5W30 as an example. In this case, the number “5” indicates the lower temperature threshold for starting the engine. But not directly, but indirectly: this number must also be subtracted from -40 °C, and we get the value -35 °C.

Explanation of the lubricant characteristics indicated on the packaging

The second number is a little more difficult to understand. It indirectly indicates the highest temperature threshold at which the lubricant in question can be effectively operated. In fact, this is a composite parameter that indicates the minimum/maximum viscosity within the operating temperature range from 100 °C to 150 °C. Here are just a few characteristics of oil viscosity depending on the temperature limits indicated in the indices:

• 0W30 - from the lower temperature limit -40 °C to the upper limit +30 °C;
• 5W40 - from -35 °C to +40 °C;
• 10W 40 - from -30 °C to +40 °C;
• 10W50 - from -30 °C to +50 °C;
• 15W60 - from -25 °C to +60 °C.

What is oil used for?

Initially, lubricating fluids were used to remove heat from the working area and draw it into the crankcase, reduce friction of parts in the assembly, remove wear products and protect the crankshaft journals.

Subsequently, the oil was assigned the role of lubricating all elements of the gas distribution mechanism and engine cylinders. At the present stage, motor oils are an integral component of the operation of all machine mechanisms.

Let us denote the specific protective functions performed by motor oil:

• Formation of a film on parts that protects against friction and wear;
• Prevention of oxidation processes and corrosion of components;
• Cleaning important work areas from contamination - soot, dirt, carbon deposits and other products of fuel combustion;
• Removal of contaminant particles remaining during wear of components;
• Preservation of components from overheating;
• Ensuring reliable starting;
• Reduced “injury” to parts during cold starts.

Therefore, today's car enthusiast is far from indifferent to what is poured into the working units. The most important criterion for selecting a lubricant composition is the viscosity of the oil.

High temperature performance

The viscosity of engine oil over the operating temperature range of the engine has no relation to the ambient temperature. It is almost the same both at 10 degrees below zero and at 30 degrees hot. 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 of ambient temperature for a particular “summer” viscosity. A good example is a comparison of lubricating fluids with 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 in the tables at all.

This idea is wrong. In addition, the term “summer” viscosity or “summer” oil is incorrect from a professional point of view. This is explained in the video provided. The thing is that this parameter represents a regime 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 oil fluid 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/sec. The area of ​​each layer is 1 cm2. In other words, tests carried out using special devices (rotational viscometers) make it possible to simulate 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 certain values ​​are determined.

The table reflects the kinematic and dynamic viscosity technical parameters at certain temperatures (+100 and +150°C), as well as a 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 car oil turns out to be. In simple terms, the viscosity level at high temperatures provides information about the thickness of the oil film between the gaps and how strong it is. Today, the SAE specification provides for 5 levels of high-temperature viscosity indicators of oils for automobiles - 20, 30, 40, 50 and 60.

Some useful tips when selecting oil by viscosity

The main temperature-viscosity characteristics are usually included in the instructions that are included in the commercial lubricant kit. It is necessary to check these indicators with the corresponding sections in the vehicle operating instructions. If you are forced to change the brand of the substance used on a car with significant mileage, it is recommended to choose a thicker product.

For pronounced sports cars, experienced specialists recommend using lubricants with a high temperature viscosity index. However, such oil is not suitable for conventional serial power plants.

It is strictly not recommended to fill the lubrication system of a car engine with an oil mixture whose viscosity differs from the viscosity officially recommended by the car manufacturer. You should always remember that any deviations from the specified technological ratings sooner or later lead to unpleasant breakdowns.

Thus, following the international classification and the advice of experienced professionals, every motorist will be able to protect himself from unexpected malfunctions of the “heart” of any car - its engine. A correctly selected engine oil viscosity grade is the key to long-term and flawless operation of the entire power unit.