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:

1. 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),
2. oil temperature rises
3. the degree of its viscosity decreases (fluidity increases),
4. the thickness of the oil layer decreases (leaks into the inter-part gaps),
5. friction force is reduced
6. 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.

Engine oil classes

• winter "W"
• summer
• all season

crankability

Pumpability

Kinematic viscosity

Dynamic Viscosity HTHS

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Specification of engine oils according to SAE (in terms of viscosity)

SAE (Society of Automotive Engineers - Society of Automotive Engineers). The SAE J300 specification is the international standard for classifying motor oils.

Oil viscosity is the most important characteristic of engine oil, which determines the ability of the oil to ensure stable engine operation, both in cold weather (cold start) and in hot weather (at maximum load).

The temperature indicators of engine oil basically contain two main values: kinematic viscosity (the ease of oil flow at a given temperature under the influence of gravity) and dynamic viscosity (shows the dependence of the change in oil viscosity on the speed of movement of lubricated parts relative to each other). The higher the speed, the lower the viscosity, the lower the speed, the higher the viscosity.

Engine oil classes

• winter "W"– Winter-Winter (SAE 0W, 5W, 10W, 15W, 20W, 25W). These motor oils are characterized by low viscosity, provide safe cold start at temperatures below zero, but do not provide good enough lubrication of parts in summer.
• summer(SAE 20, 30, 40, 50, 60). Oils of this class are characterized by high viscosity.
• all season(SAE 0W-20, 0W-30, 0W-40, 0W-50, 0W-60, 5W-20, 5W-30, 5W-40, 5W-50, 5W-60, 10W-20, 10W-30, 10W-40, 10W-50, 10W-60, 15W-30, 15W-40, 15W-50, 15W-60, 20W-30, 20W-40, 20W-50, 20W-60). Combines the characteristics of both summer and winter motor oils.

Viscosity properties at specified low temperatures

crankability determined using a cold start simulator (cold cranking from the starter) CCS (Cold Cranking Simulator). An indicator of the dynamic viscosity of the oil and the temperature at which the oil has sufficient fluidity to ensure safe starting of the engine.

Pumpability determined by referring to the readings of the mini-rotational viscometer MRV (Mini-Rotary Viscometer) - 5Co below. The ability to pump oil by a pump in the engine through the lubrication system, eliminating the possibility of dry friction of parts.

Viscosity properties at specified high temperatures

Kinematic viscosity at a temperature of 100 degrees Celsius. Shows the minimum and maximum values ​​​​of engine oil viscosity when the engine is warm.

Dynamic Viscosity HTHS(High Temperature High Shear) at 150 degrees Celsius, and a shear rate of 106 s-1. Determines the energy saving properties of engine oil. A measure of the stability of viscosity characteristics at extreme temperatures.

An important indicator of lubricating properties is the viscosity of the oil. It is determined by the chemical composition and structure of the compounds in the lubricant. In fact, the extent to which the liquid lubricates the surfaces of the rubbing parts of the power unit depends on this characteristic. Its properties are influenced by external factors such as temperature, load and shear rate. That is why, next to the specific value, the test conditions are indicated.

What is the kinematic and dynamic viscosity of the oil?

In order to understand the difference, let's look at their characteristics.
The kinematic viscosity of an engine oil, which is measured in mm2 / s (cST), indicates its fluidity at normal and high temperatures. To measure this indicator, a glass viscometer is used. Note the time during which the lubricant flows down the capillary at a given temperature. In this case, a low shear rate is used and the kinematic viscosity of the oil is measured at 100°C.

Dynamic viscosity is measured with a rotational viscometer that simulates conditions that are as close to real as possible.

The methods that determine the viscosity of an engine oil are pre-established in the SAE J300 APR97 specification. Following this particular certification, all lubricating fluids are divided into 3 types:
- summer;
- winter;
- all season.

If only numbers are used in the name, for example, SAE 30, SAE 50, etc., then these fluids refer to summer motor lubricants. If the number and letter W are used, for example, SAE 5W SAE 10W - winter lubricants. When 2 of these types are used in the class designation, such a liquid is called all-weather.

Let's take a look below at what SAE oil viscosities mean.
The SAE classification (Association of Automotive Engineers) separates all oils according to their ability to remain in a liquid state (flow), and lubricate well all parts of the power unit at different temperatures.

The above are temperature readings, depending on the value that determines the viscosity of the engine oil. The table shows at what temperature the fluidity of a particular fluid will not lose its lubricating properties.

Why is the viscosity of the oil important when changing the lubricant and what do the numbers mean?

A simple example to illustrate. As you know, the low viscosity of engine oil contributes to their normal operation in winter (SAE 0W, 5W). If the fluidity is low, accordingly, the oil film covering the parts of the power unit will be thin. The manufacturer in the technical manual indicates the permissible values, as well as tolerances for each type of engine. If you fill in a high fluidity grease, the motor will work with a load at an elevated temperature. This drastically reduces its motor resource.

And now vice versa. You are pouring liquid with fluidity below the indicated level. In this case, breaks in the lubricating film occur during operation, and the motor may jam. Oil viscosity as a function of temperature. No need to think that filling the engine with "super grease", which is used on sports cars, your car will start to "fly". It is necessary to fill in the fluid recommended by the manufacturer.
Another misconception is that some motorists do not distinguish the type of lubricants from their fluidity. So, for example, the viscosity of synthetic oils can be the same as mineral or semi-synthetic. In this case, they differ in composition, not physical properties.

What oil viscosity to choose for your car engine.

First of all, you need to look at the technical manual. The manufacturer indicates in the manual which oil viscosity is best suited for the engine in order to ensure its long-term operation. If it is not possible to see the recommended oil viscosity, then it is important to determine a few points:

• at what minimum and maximum temperatures your car will be operated;
• whether a load will be used (trailer, additional load or off-road driving);
• What is the condition of the engine (new or used).

Following these indicators, you must choose the viscosity of the car oil that will ideally lubricate the parts of the power unit.

A few words about other types of lubricants

transmission fluids

Transmission fluids meet SAE J306 classification. The viscosity of the gear oil depends on the operating temperature. As well as motor, transmission fluids are conventionally divided into:

• winter (SAE 70W, 75W, 80W, 85W);
• summer (SAE 80, 85, 90, 140, 250);
• combined (for example, SAE 75W-85).

To understand what kind of lubricant to use in the box of your car, you need to look at the recommendations and approvals of the gearbox manufacturer.

Hydraulic Lubricants

In addition to their primary function of transmitting pressure, hydraulic fluids also lubricate hydraulic pump parts. Based on this, they are divided into classes. The viscosity of hydraulic oil is low, medium and high. Below is a table showing the possible classes of hydraulic lubricating fluids.

The vast majority of car owners who are engaged in the independent selection of lubricants for their car, at least have a general idea of ​​​​such a concept as SAE classification.

The engine oil viscosity table, provided by the SAE J300 standard, subdivides all lubricants for engines and transmissions of automobiles, depending on the degree of fluidity at a certain temperature. Moreover, this division also determines the temperature framework for the use of a particular oil.

Today we will take a closer look at what the classification of lubricants is according to the table from the SAE J300 standard, and also analyze what meaning the values ​​​​indicated in it carry.

What is a viscosity table

For ordinary motorists who are not engaged in a detailed study of the parameters of engine oils, the SAE oil viscosity table means the temperature range at which it is allowed to be filled into the power unit.

In a general sense, this is a correct statement. However, upon closer examination, it becomes clear that the data in the table do not quite correspond to the generally accepted opinion.

First, let's look at what the SAE oil viscosity table includes. It has a separation in two planes: vertical and horizontal.

The classic version of the table is divided by a horizontal line into winter and summer lubricants (in the upper part of the table there are winter lubricants, in the lower part - summer and all-season lubricants). Vertically, there is a division into restrictions when using lubricants at temperatures above and below zero (the line itself passes through the 0 ° C mark).

On the Internet, and some printed sources, two different versions of this table are often found. For example, for an oil with a viscosity of 5W-30 in one of the versions of the graphic design of the SAE J300 standard, it is able to operate at temperatures from -35 to +35 ° C.

Other sources limit the scope of 5W-30 oil to the range from -30 to +40 ° C.

Why is this happening?

A completely logical conclusion suggests itself: there is an error in one of the sources. But if you delve into the study of the topic, you can come to an unexpected conclusion: both tables are correct, let's figure it out.

Detailed consideration of the parameters indicated in the table

The fact is that when the tables were designed and the algorithm for creating the dependence of oil viscosity on temperature was considered, the automotive technologies available at that time were taken into account.

That is, at the end of the 20th century, all engines were built using approximately the same technology. The temperature, contact load, pressure created by the oil pump, the scheme and design of the lines were approximately at the same technological level.

It was under the technology of that time that the first tables were created linking the viscosity of the oil and the temperature at which it can be operated. Although in fact the SAE standard in its pure form is not tied to the ambient temperature, but only stipulates the viscosity of the oil at a certain temperature.

The meaning of letters and numbers on the canister

The SAE classification includes two values: the number and the letter "W" - the winter viscosity coefficient, the number following the letter "W" - the summer one. And each of these indicators is complex, that is, it includes not one parameter, but several.

The winter coefficient (with the letter "W") includes the following parameters:

• viscosity when pumping lubricant along the lines with an oil pump;
• viscosity when cranking the crankshaft (for modern engines, this indicator is taken into account in the main and connecting rod journals, as well as in the camshaft journals).

What the numbers on the canister say - video

The summer coefficient (going with a hyphen after the letter "W") includes two main parameters, one secondary, and one derivative calculated from the previous parameters:

• kinematic viscosity at 100 °C (that is, at the average operating temperature in a heated internal combustion engine);
• dynamic viscosity at 150 °C (determined to represent the viscosity of the oil in the ring/cylinder friction pair, one of the key components in engine operation);
• kinematic viscosity at a temperature of 40 ° C (shows how the oil will behave at the time of the summer start-up of the engine, and is also used to study the rate of spontaneous flow of the oil film into the sump under the influence of time);
• viscosity index - indicates the property of the lubricant to remain stable when the operating temperature changes.

Often, several values ​​​​are provided for the winter temperature limit. For example, for 5W-30 oil taken as an example, the permissible ambient temperature with guaranteed pumping of lubricant through the system should not be lower than -35 ° C. And for guaranteed cranking of the crankshaft by a starter - not lower than -30 ° C.

SAE class	Viscosity low temperature		Viscosity high temperature
	cranking	Pumpability	Viscosity, mm2/s at t=100°С		Min viscosity HTHS, mPa*s at t=150°С and speed shift 10**6 s**-1
	Max viscosity, mPa*s, at temperature, °C		Min	max
0W	6200 at -35 °C	60000 at -40 °C	3,8	-	-
5W	6600 at -30 °С	60000 at -35 °С	3,8	-	-
10W	7000 at -25 °C	60000 at -30 °С	4,1	-	-
15W	7000 at -20 °С	60000 at -25 °C	5,6	-	-
20W	9500 at -15 °C	60000 at -20 °С	5,6	-	-
25W	13000 at -10 °C	60000 at -15 °С	9,2	-	-
20	-	-	5,6		2,6
30	-	-	9,3		2,9
40	-	-	12,5		3.5 (0W-40; 5W-40; 10W-40)
40	-	-	12,5		3.7 (15W-40; 20W-40; 25W-40)
50	-	-	16,3		3,7
60	-	-	21,9		3,7

This is where conflicting readings arise in the oil viscosity tables posted on different resources. The second significant reason for the different values ​​​​in the viscosity tables is the change in engine production technology and the requirements for viscosity parameters. But more on that below.

Methods of determination and the attached physical meaning

Today, for automotive oils, several methods have been developed for determining all viscosity indicators provided for by the standard. All measurements are carried out on special devices - viscometers.

Depending on the investigated quantity, viscometers of various designs can be used. Let's consider several methods for determining viscosity and the practical meaning that lies in these values.

Viscosity when cranking

Lubrication in the necks of the crankshaft and camshaft, as well as in the swivel joint of the piston and connecting rod, thickens strongly with decreasing temperature. Thick oil has a large internal resistance to displacement of the layers relative to each other.

When you try to start the engine in winter, the starter noticeably strains. Grease resists crankshaft rotation and cannot form a so-called oil wedge in the main journals.

A rotary viscometer type CCS is used to simulate cranking conditions. The viscosity value obtained by measuring it for each parameter from the SAE table is limited and in practice means how much the oil is capable of providing cold cranking of the crankshaft at a particular ambient temperature.

Pumping viscosity

Measured in a rotational viscometer type MRV. The oil pump is able to start pumping lubricant into the system up to a certain thickening threshold. After this threshold, effective pumping of the lubricant and its pushing through the channels is difficult or completely paralyzed.

Here, the generally accepted maximum viscosity value is 60,000 mPa s. With this indicator, free pumping of lubricant through the system and its delivery through the channels to all rubbing nodes is guaranteed.

Kinematic viscosity

At a temperature of 100 °C, it determines the properties of the oil in many units, since this temperature is relevant for most friction pairs during stable engine operation.

For example, at 100 °C it affects the formation of an oil wedge, the lubricating and protective properties in friction pairs of the connecting rod pin / bearing, crankshaft journal / bearing, camshaft / beds and covers, etc.

Automated capillary viscometer and kinematic viscosity viscometer AKV-202

It is this parameter of kinematic viscosity at 100 °C that receives the most attention. Today, it is measured mainly by automated viscometers of various designs and using various techniques.

Kinematic viscosity at 40 °C. Determines the thickness of the oil at 40 °C (i.e. approximately at the time of summer start-up) and its ability to reliably protect engine parts. It is measured in the same way as the previous paragraph.

Dynamic viscosity at 150 °C

The main purpose of this parameter is to understand how the oil behaves in a ring/cylinder friction pair. In this node, under normal conditions, with a fully serviceable engine, approximately this temperature is maintained. It is measured on capillary viscometers of various designs.

That is, from the foregoing, it becomes obvious that the parameters in the SAE oil viscosity table are complex, and there is no unambiguous interpretation (including regarding the temperature limits of use). The boundaries indicated in the tables are conditional and depend on many factors.

Viscosity index

An important parameter that indicates the working qualities of the oil and determines its performance properties is the viscosity index. To determine this parameter, an oil viscosity index table and a formula are used.

Applied Formula for Viscosity Index

Shows with what dynamics the oil will thicken or thin as the temperature changes. The higher this coefficient, the less susceptible the considered lubricant to thermal changes.

That is, in simple words: the oil is more stable in all temperature ranges. It is believed that the higher this index, the better and better the lubricant.

All values ​​presented in the table for calculating the viscosity index are obtained empirically. Without going into technical details, we can say this: there were two reference oils, the viscosity of which was determined under special conditions at 40 and 100 ° C.

Based on these data, coefficients were obtained that in themselves do not carry a semantic load, but are used only to calculate the viscosity index of the oil under study.

Conclusion

In conclusion, we can say that the SAE oil viscosity table and its linkage to permissible operating temperatures currently play a very conditional role.

It would be a relatively correct step to use the data taken from it to select oil for cars at least 10 years old. For new cars, this table is better not to use.

Today, for example, 0W-20 and even 0W-16 oil is poured into new Japanese cars. Based on the table, the use of these lubricants is permissible in the summer only up to +25 ° C (according to other sources that have undergone local correction - up to +35 ° C).

That is, logically, it turns out that Japanese-made cars can hardly drive in Japan itself, where in summer the temperature can reach +40 ° C. This, of course, is not true.

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Now the relevance of the application of this table is declining. It can only be used for European cars over 10 years old. The choice of oil for a car should be based on the manufacturer's recommendations.

After all, only he knows exactly what gaps in the interfaces of the engine parts are selected, what design and power the oil pump is installed, and what capacity the oil lines are created.

Oil viscosity (fluidity) is a parameter that affects the ability of the engine mixture to maintain the specified properties at different temperatures. For the operation of the motor, this indicator plays a very important role, the lubrication of the drive parts and its protection from wear depend on it.

When choosing car oil, keep in mind that liquids are characterized by two parameters:

1. Kinematic viscosity, which refers to the fluidity of a mixture under the action of gravity, indicates how easily the fluid will flow in various parts of the engine and lubrication system, measured in mm 2 / s.

2. Dynamic viscosity - a parameter showing changes in the strength of the oil film under load: with an increase in the speed of movement of the lubricated elements relative to each other, the viscosity decreases, measured in Pa * s.

Engineers have developed a classification of SAE motor mixtures. According to this system, all motor oils are divided into three classes depending on the viscosity index (changes in oil properties at different temperatures). See table 1 for the characteristics of motor oils according to SAE.

Table 1. SAE specification.

What does the viscosity of oils mean, you can find out by watching the video:

Oils for different seasons

The first class is winter liquids, their marking consists of a number and the letter w next to it, for example, 5w, 20w. The number indicates an indicator of sub-zero temperature, at which the liquid does not crystallize, performs its functions, the letter w means winter (from the English winter).

These motor oils are characterized by a kinematic viscosity index at a temperature of 100 0 C and two low-temperature dynamic viscosity values:

• turning, means the temperature at which the liquid does not thicken, will ensure the start of the drive without warming up;
• pumping - an index indicating the temperature regime at which the mixture will normally flow through the lubrication system and ensure the formation of a protective film on the elements of the power unit.

The second class is summer blends. Their marking consists of the abbreviation SAE and a number next to it, for example, SAE 20, 40, 50. The number in the marking means an indicator of positive temperature at which the mixture will have sufficient density to form a film on the motor elements to protect it from wear. The larger the number in the designation, the higher the viscosity index of the oil. Visually, the difference in this parameter is shown in Figure 1, it shows flasks with different motor oils used in the summer and balls with the same weight, simultaneously thrown into the flasks. The picture shows that the thicker the liquid, the slower the ball will be at the bottom of the container.

Figure 1. Oils with different fluidity.

The third class is all-weather mixtures. Their marking consists of the designation of the previous two classes, for example, 10w - 30. 10w means a negative temperature indicator at which the mixture will start the power unit without warming up and pump fluid through the lubrication system. The number 30 means a positive temperature indicator at which the car oil will be dense enough to protect the engine from overheating. You can determine the maximum negative temperature if you subtract the number 35 from the number in the marking, for example, for 10w - 30 this mathematical action will look like this: 35-10 \u003d 20 (which means that 20 is a negative temperature equal to -20 0 С).

The temperature range at which the mixtures will not lose their protective and antiwear properties are shown in Table 2.

Table 2. Limit of operating temperatures for motor fluids.

All-weather fluids have a wider temperature range than winter or summer grades. This difference is explained by the base of automobile oil, liquids with a synthetic base have molecules of the same size in their structure, therefore, when exposed to temperature, their viscosity practically does not change. Mineral mixtures do not have uniformity in the structure of molecules; at high temperatures, they liquefy faster. There are many factors to consider when choosing the right fluid.

The choice of car oil

It is necessary to select the machine mixture taking into account its structure. If you choose an oil that is too viscous, then it will not be able to form a protective film on the drive elements, it will not fill the gaps in the friction units. Plus, a very dense liquid will create an additional load on the motor - this will reduce its resource. A too liquid mixture will not fill the gaps in the friction units properly, and the protective film formed by it will break under load.

You can determine the desired viscosity of automotive oil for your car based on the recommendations of the car dealer (this parameter is indicated in the car's service book). If the motor has passed half of its resource, then it is recommended to fill in a thicker mixture, this is due to an increase in the gaps in the friction units of the motor. It is also necessary to pay attention to the temperature outside the machine, the higher it is, the thicker the oil is needed. The dependence of the fluidity of motor fluid on temperature is shown in Table 2 and is shown in Figure 2.

Figure 2. Operating temperature range for engine mixtures.

You can determine the most suitable oil, taking into account the mileage of the car, the technical characteristics of the motor, the operating temperature range, and the recommendations of the car manufacturer.

If you are looking for a car oil for a modern engine, consider energy-saving fluids. They have a very low viscosity, reduce fuel consumption, but not all types of engines can be poured.

Choose the optimal viscosity parameter at which the mixture will withstand the load in extreme engine operating conditions, protect the power unit from overheating and does not crystallize at sub-zero temperatures outside the car in your area.