Viscosity of motor oils: designation, interpretation

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:42

Viscosity is one of the most important parameters of the oil that needs to be poured into the engine. It is not for nothing that the viscosity of engine oil is indicated on the container itself. The change in viscosity depending on temperature determines the boundaries of the temperature limits for the use of this fuel and lubricants. 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 in order to maintain the required pressure in the system and create a lubricating film between the parts in the engine that rub against each other.

Categories of oils

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

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

Viscosity of motor oils is an important, but not the only operational parameter. It is also worth considering anti-wear, anti-corrosion, detergent and antioxidant properties. Despite this, it is the viscosity characteristics of motor oils that are the most important. It is for them that drivers classify fuel and lubricants. And various additives and additives only increase the cost of the product.

Which oil is right for your car?

The basis for choosing a particular brand is the requirement of the car manufacturer. The instructions must indicate what viscosity the engine oil should have. As examples, the instructions also provide specific brands and links to websites of lubricant manufacturers.

In the event that the car is old, and you can’t find official instructions for the type and brand of oil used, you can do it yourselfchoose the brand of oil for the transmission and engine. At any point of sale or at the service station they will be able to give qualified advice.

SAE Engine Oil Viscosity

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

The SAE standard evaluates the following lubricant parameters:

1. Kinematic viscosity. This parameter characterizes the compliance of the product with one or another viscosity class. This is the main indicator for all fuels and should not be confused with the dynamic viscosity of engine oil, which determines the drag force of two oil layers.
2. Pumpability. Determines the speed at which oil enters the friction pairs when starting the engine on a cold one. There is also a possibility of motor failure due to the rotation of the liners during start-up.
3. Viscosity at high temperatures. Reflects true viscosity in high temperature service. The parameter also characterizes anti-wear properties.

In fact, SAE is the viscosity rating of lubricants. Today there are 5 summer classes and 6 winter ones. In the designation of the viscosity of winter-type motor oils, the English letter W is always present, which means Winter (Winter). And what will be morehigh viscosity, the higher the number indicated in the specification.

Deciphering engine oil viscosity

First, let's define winter and summer classes. Winter classes include oils:

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

Summer lubricants:

• 20;
• 30;
• 40;
• 50;
• 60.

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

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

The designation 40 in our example indicates the summer class of the product. Therefore, this oil is universal. This parameter determines how well the oil performs at high engine temperatures.

The presence in the name of the designations of both classes indicates the all-season fuel and lubricants. The same can be said about the viscosity of 5W40 engine oil. It is a multigrade oil that can operate in both high and very low temperatures.

How to determine the viscosity of engine oil for yourcar?

It is best to follow the manufacturer's recommendations when choosing engine oil. Judging by these recommendations, your car will be insured against problems with starting the engine in winter. This will eliminate the negative consequences for the engine associated with oil starvation. If you use oils of the wrong viscosity, then increased engine wear and even jamming after starting is possible. It should be remembered that after starting the motor, the pump needs some time to pump oil through the system. Only then will it go to the rubbing parts. And if the viscosity is too high, then the pump will take much longer. All this time, the motor will be in oil “starvation” mode, due to which the rubbing parts will quickly become unusable. The best winter oil is one that is able to maintain its fluidity even in cold weather. The best in this case are “0W” class lubricants.

Viscosity scale of oils depending on temperature

If you have no recommendations or there is no instruction at all, then you can either seek advice from the service station (the simplest and most concise option), or try to determine this parameter yourself.

First of all, you should find information about the average winter temperatures in your area where you plan to drive. Depending on this, you need to select oil.

This is how the engine oil viscosity scale looks like:

About choosing summer oil

When choosing fuel and lubricants for summer operation of a car, it is worthkeep in mind that most well-known European concerns recommend the use of class “40” lubricants. This is due to the fact that in summer and even in spring or autumn, the thermal stress of the engines is high. High temperatures, shear rates in different areas of the motor, as well as huge specific pressures - all this is characteristic of modern motors. Under these conditions, the oil must retain its properties and keep the necessary oil film, as well as cool friction pairs. This task becomes difficult when operating the motor in extreme heat or being in a traffic jam, where there is no natural active cooling of the motor by the flow of oncoming air.

All-weather oils have the properties of summer and winter varieties of lubricants. They have dual SAE designations. For example, in the designation of the viscosity of 5W30 engine oil, there are two designations at once. Here, winter viscosity and temperature properties are reflected on the left side, and summer properties on the right.

Viscosity-temperature properties

This is one of the key characteristics of the oil. It is on these properties that the temperature range depends, in which this fuel and lubricants will ensure a normal start of the engine without warming it up, as well as efficient pumping of oil through the lubrication system, cooling of rubbing parts at the highest loads and temperatures.

Even if the car is operated in a country with a temperate climate, the temperature range from cold start in winter to maximum warm-up can be 180-190 degrees. Viscositymineral oil in the temperature range from -30 to +150 degrees can vary thousands of times. Summer oils, which have sufficient viscosity at high temperatures, will ensure normal engine start at an ambient temperature of 0 degrees. Winter fuels and lubricants, which will ensure a cold start of the engine at low temperatures, will have insufficient viscosity when heated.

Therefore, seasonal oils need to be changed 2 times a year. Moreover, their operating time does not play any role at all. Even if the car has been in the garage all winter with winter oil, it must be replaced when warmer weather sets in. Because of this, the operation of engines becomes quite expensive.

This problem is partly solved thanks to special polymer additives. Therefore, in universal fuels and lubricants such as 10W40 there will always be additives. Without them, the oil cannot be universal and work equally well in winter and summer.

Conclusion

Now you know the decoding of the viscosity of engine oil and you can choose the right fuel and lubricants for yourself. But if there is any doubt about the choice of the correct viscosity, then it is better to contact a specialist. Incorrectly selected fuels and lubricants can seriously damage the engine.