/ Density of engine oil. How and for what it is necessary to determine the density of motor oil?

Density of engine oil. How and for what it is necessary to determine the density of motor oil?

When choosing engine oil motoristsare guided by different indicators. For the gasoline unit on the package the index S is indicated, for the diesel engine - C. They are also oriented to other indicators. For example, a synthetic, semi-synthetic or mineral base is chosen; oil of different viscosities depending on the warm or cold season. But often choose the appeared in recent years, all-season lubricating fluids. At the same time, they are guided by the viscosity index, which is recommended by the manufacturer.

There is another important indicator - the density of motor oil. About it and will be discussed in the article.

Basic properties of oils

Density of engine oil

Among the main characteristics relating to lubricating fluids, the following indicators are distinguished:

  • Density of engine oil and specific gravity. The first term refers to the ratio to the volume of the mass. Density is measured in kilograms per cubic meter. Here it is worth noting the specific weight, meaning the ratio of the mass of matter to the mass of water. Both properties depend on temperature.
  • Viscosity is the value through which is expressedfluidity. It also depends on the temperature. Viscosity is measured in several units: in Stokes, centistokes and square meters or millimeters per second according to the SI measurement system.
  • Flash point and freeze point. The first means such an increase in temperature, at which vapors flare up when an open fire is presented. The second indicator is a low temperature, at which the oil has not completely lost its fluidity. This can be demonstrated by tilting the tube.
  • The acidic and alkaline number indicates the amount of product needed to neutralize, due to the fact that acidic and alkaline products accumulate in the lubricating fluid during operation.


The density of the engine oil is very importantan index expressing the ratio of mass to volume. It is related to the compressibility and viscosity. The parameter significantly affects the power supplied during hydrotransmission, and expresses the energy reserve during circulation. At high density, it is possible to reduce the dimensions of the hydrotransmission without changing the power. With increasing pressure, density also begins to increase.

If the density of the engine oil changes at 20degrees, we can talk about malfunctions in the motor. Given the comparison of the density of gasoline and diesel fuel with the density of oil, it turns out that the latter indicator will be higher. Thus, the ingress of fuel into the lubricating fluid will reduce the density value. At the same time, water, which has almost 1000 kg / m3, on the contrary, will increase it. This will be the case because it has a greater value than the density of engine oil kg / m3 (it has only 880). Taking into account these features, it is possible to calculate, for example, malfunctions in crankcase ventilation or engine cooling system.

Relationship between density and viscosity

Classification of motor densityoil, does not exist. But there is another, called SAE. It determines the lubricating fluid according to the viscosity parameter. Winter oils are identified by the presence of the letter W. They are subdivided from 5W to 25W. For example, an oil with the designation 5W is able to work at winter temperatures to thirty degrees below zero. A designation 10W means the ability to work up to minus twenty degrees. But the engine oil, which has a 20W, will work properly only at very low temperatures. It is not recommended to refuel if the weather is at risk of being too cold.

engine oil waste

The designation of summer oils usually ranges from 10 to 60. At high temperatures, the lubricating fluid must have low viscosity properties.

Density of some all-weather

Despite the fact that the density of engine oilspent does not depend on the viscosity index, it is possible to identify certain regularities by marking. In addition, the manufacturer indicates this figure in the technical specifications.

For example, it is known that 0,87-0,9 ischaracteristic density of engine oil 15W40 at fifteen degrees. The index of 0.857 kg will often be at the winter mark of 10W. And about 0.85 will be the density of engine oil 5W40.

engine oil density 15W40

The summer figure at twenty will be equal to 0,861 kg / l, and at fifty - 0,875 kg / l.

Recently, the most widespreaddistribution receive lubricating fluids having the ability to work equally well in the summer and winter, the so-called all-season oils. Their use has greatly simplified the life of car enthusiasts, who now do not need to be afraid that they will forget to change the fluid when the hot season comes on or, conversely, cold.


To measure the density, a device called a hydrometer is used. This is a float made of glass, with ballast below, a thermometer in the middle and a thin tube with a scale at the top.

The instrument is placed in oil for a period of three to fiveminutes and take the reading on the scale. The density of motor oil (kg / l) is indicated at a temperature of two hundred degrees. If the measurements were taken at a different temperature, the result is adjusted according to the corresponding table in GOST.

Measurement of density

To determine the properties of the lubricating fluid, its relative density, calculated from the ratio of the oil density to the density of water at a temperature of forty degrees (with equal volumes), is used.

Density of motor diesel oil

The density is measured as follows.

  1. The oil is poured into the glass flask at a temperature of twenty degrees.
  2. Carefully lower the hydrometer so that it does not touch the walls of the vessel.
  3. After a few minutes, while holding the device at eye level, make a measurement, while taking the temperature reading. Density is determined by a special table.

For example, it is known that the density of motor diesel oil varies from 890 to 920 kg / m3, and of automobile gasoline - from 910 to 930 kg / m3.

Density of engine oil at 20 degrees

This parameter helps you compare the properties of differentlubricating fluids. However, one can not judge it on the quality of the oil as a whole. For this, color, product transparency and other indicators are taken into account.

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