Viscosity of motor oils: designation, decoding

Viscosity is one of the most important parametersoil, which must be poured into the engine. It's not for nothing that the viscosity of the engine oil is indicated on the tank itself. The change in viscosity as a function of temperature determines the limits of the temperature limits for the application of this fuel. At low temperatures, the viscosity of the oil should not be very high, so that the engine can start "cold" (from the starter), and the pump can pump it through the system. And at high temperatures, the viscosity of this lubricant should not be low to provide the required pressure in the system and create a lubricating film between the parts in the engine that rub against each other.

dynamic viscosity of engine oil

Oil Categories

Depending on how this fuel changes with temperature, there are different categories:

  1. Winter. These oils have a low viscosity, so whencold temperature on the street the engine with them easily starts. However, at high temperatures, such oils are not able to ensure normal operation of the engine. The viscosity of this type of engine oil will be very low at high temperatures, so it can not create a reliable oil film between the engine parts.
  2. Summer. At a low temperature outside (in winter, for example), these oils will not provide a cold start, but work well at high temperature due to high viscosity.
  3. All-season. These are universal lubricants thatAt low temperatures they have the viscosity of winter oils, while at high temperatures they have a viscosity of summer oils. These lubricants are the most popular, because they do not need to be changed every season, and they are very effective as energy-saving.

Viscosity of motor oils is important, but notthe only operational parameter. It is also worth considering antiwear, anti-corrosion, detergent and antioxidant properties. Despite this, it is the characteristics of engine oils in viscosity are the most important. It is for them that drivers classify fuels and lubricants. And various additives and additives only increase the cost of the product.

viscosity of motor oils

Which oil is suitable for your car?

The basis for choosing a particular brand iscar manufacturer's request. The instructions must indicate the viscosity of the engine oil. As examples, the instructions also provide specific brands and links to lubricant manufacturers' websites.

In the event that the car is old, and findofficial instructions on the type and brand of used oil can not, you can independently choose a brand of oil for the transmission and engine. At any point of sale or at the service station will be able to give qualified advice.

Viscosity of SAE engine oil

engine oil viscosity 5w40

SAE (Society of Automobile Engineers) isan international standard that regulates the viscosity of oils. Many drivers assume that this is a manufacturer or brand of lubricant, but it is not. The SAE specification can not say anything about the quality of the oil or its purpose for a specific engine type.

The SAE standard estimates the following lubricant parameters:

  1. Kinematic viscosity. This parameter characterizes the conformity of the product to a particular class of viscosity. This is the main indicator for all fuel options, and it should not be confused with the dynamic viscosity of the engine oil, which determines the strength of the resistance of the two oil layers.
  2. Pumping capacity. Determines the speed at which oil flows to friction pairs when the engine is started on a cold one. Also, there is a probability of failure of the motor due to rotation of the liners during start-up.
  3. Viscosity at high temperatures. Reflects the present viscosity at high temperatures. The parameter also characterizes the anti-wear properties.

In fact, SAE are the characteristics of lubricationmaterials on the viscosity. Today there are 5 summer classes and 6 winter classes. In the designation of viscosity of motor oils of winter type, there is necessarily an English letter W, which means Winter. And the higher the viscosity, the higher the number indicated in the specification.

interpretation of engine oil viscosity

Explanation of engine oil viscosity

First, we define winter and summer classes. The winter classes include oils:

  • 0W;
  • 5W;
  • 10W;
  • 15W;
  • 20W;
  • 25W.

Summer Lubricants:

  • 20;
  • thirty;
  • 40;
  • 50;
  • 60.

To make things easier for you, let's give a simplean example of a lubricant characteristic. Let's try to understand what the viscosity of engine oil SAE 10W-40 means. Note that the product with this characteristic is most often used in Russia.

So, 10W in the notation gives us to understand that thisoil is winter. On how correctly you can determine this parameter, will depend on the ability to easily start the engine in the cold without negative consequences for it.

The designation 40 in our example refers to the summerclass product. Consequently, this oil is universal. This parameter determines how well the oil is operating in the high temperature mode of the motor.

which means the viscosity of the engine oil

The presence in the name of the designations of both classesspeaks about all-weather fuel. The same can be said about the viscosity of the engine oil 5W40. This is a multigrade oil that can work both at high and very low temperatures.

How to determine the viscosity of motor oil for your car?

The best thing when choosing engine oilfollow the manufacturer's advice. Judging by these recommendations, your car will be insured against problems with starting the engine in the winter. This will eliminate the negative effects on the engine associated with oil starvation. If oils of inappropriate viscosity are used, increased wear of the motor and even jamming after start-up is possible. It should be remembered that after starting the motor the pump needs some time to pump the oil through the system. Only then it will go to the rubbing details. And if the viscosity is too high, the pump will take much longer. All this time the motor will be in the mode of oil "starvation", because of which the rubbing parts will quickly become worthless. The best winter oil is one that is able to maintain its fluidity even in frosts. The best in this case are greases of "0W" class.

Scale of viscosity of oils depending on temperature

If you do not have any recommendations or instructionsthere is no anyway, then you can either ask for advice in the SRT (the simplest and concise option), or try to determine this parameter yourself.

First of all, it is worth finding information on the average values ​​of winter temperatures in your region, where you plan to drive a car. Depending on this, you need to select oil.

This is how the viscosity scale of motor oils looks:

viscosity of motor oils

About the choice of summer oil

When choosing fuel for the summer operation of the carit is worth considering that most of the well-known European concerns recommend using lubricants of the "40" class. This is due to the fact that in the summer and even spring or autumn time the thermal tension of the engines is high. High temperatures, shear rates in different engine zones, as well as huge specific pressures - all this is typical of modern motors. Under these conditions, the oil should retain its properties and keep the necessary oil film, and also cool the friction pairs. This task becomes difficult when the motor is operated in extreme heat or in a traffic jam where there is no natural active cooling of the motor by the flow of counter air.

All-season oils have the properties of summer andwinter varieties of lubricants. For these, double SAE designations are provided. For example, in the designation of the viscosity of motor oil 5W30 there are at once two designations. Here the winter viscosity and temperature properties are reflected in the left part, and the summer ones in the right.

how to determine the viscosity of engine oil

Viscosity-temperature properties

This is one of the key characteristics of the oil. It is these properties that determine the temperature range in which this fuel will ensure the normal start of the engine without its warming up, as well as efficient oil pumping through the lubricating system, cooling of friction parts at the greatest loads and temperature.

Even if the caris operated in a country with a temperate climate, the temperature range from cold start in winter to maximum warm-up may be 180-190 degrees. Viscosity of mineral oil in the temperature range from -30 to +150 degrees can vary thousands of times. Summer oils, which have a high viscosity at high temperatures, will ensure a normal start of the motor at an ambient temperature of 0 degrees. Winter fuel, which will ensure cold start of the engine at negative temperatures, will have insufficient viscosity when heated.

Therefore, seasonal oils need to be changed 2 times a year. And their work does not play any role at all. Even if the car was standing in the garage all winter with winter oil, it must be replaced at the onset of heat. Because of this, the operation of the engines becomes quite expensive.

This problem is partly solved by specialpolymeric additives. Therefore, in universal fuels of type 10W40 there will always be additives. Without them, oil can not be universal and equally good to work in winter and summer.


Now you know the interpretation of the viscosity of the motoroil and you can pick up the right fuel. But if there is any doubt regarding the choice of the correct viscosity, it is better to consult a specialist. Incorrectly selected fuel and lubricants can seriously damage the engine.

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