When choosing engine oil, motorists are guided by different indicators. For a gasoline unit, the index on the package indicates S, for a diesel engine - C. They also focus on other indicators. For example, a synthetic, semi-synthetic or mineral base is selected; oil of different viscosity depending on the warm or cold season. But often choose all-season lubricants that have appeared in recent years. In this case, they are guided by the viscosity index recommended by the manufacturer.
There is another important indicator - this is the density of engine oil. It will be discussed in the article.
Basic properties of oils
Among the main characteristics related to lubricating fluids, the following indicators are distinguished:
- Engine oil density and specific gravity. The first term refers to the volume of the mass. Density is measured in kilograms per cubic meter. Here, it is worth noting the specific gravity, which means the ratio of the mass of a substance to the mass of water. Both properties are temperature dependent.
- Viscosity is the value through which fluidity is expressed. It also depends on 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 solidification. The first means an increase in temperature at which vapors are released that flash when an open flame is offered. The second indicator is the low temperature at which the oil has not completely lost fluidity. This can be demonstrated by tilting the tube.
- The acid and alkaline numbers indicate the amount of product needed to neutralize, due to the fact that acid and alkaline products accumulate in the lubricating fluid during operation.
Density
The density of motor oil is a very important indicator expressing the ratio of mass to volume. It is associated with compressibility and viscosity. The parameter significantly affects the power supplied by the hydraulic transmission, and expresses the energy reserve during circulation. At high density, it is possible to reduce the size of the hydraulic transmission without changing the power. With increasing pressure, the density also begins to increase.
If the density of the engine oil changes at 20 degrees, we can talk about malfunctions in the engine. 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 having almost 1000 kg / m3, on the contrary, will increase it. This will take place 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 the crankcase ventilation or engine cooling system.
The relationship of density and viscosity
There is no classification for engine oil density. But there is another, called SAE. It determines the lubricant by the viscosity parameter. Winter oils are identified by the presence of the letter W. They are divided from 5W to 25W. For example, oil with the designation 5W is able to work at winter temperatures up to thirty degrees below zero. And the designation 10W means the ability to work up to minus twenty degrees. But engine oil, which has an indicator of 20W, will work properly only in very small frosts. It is not recommended to refuel it if the weather risks being too cold.
The designation of summer oils usually ranges from 10 to 60. At high temperatures, the lubricating fluid should have low viscosity properties.
The density of some all-season
Despite the fact that the density of used engine oil does not depend on the viscosity index, some patterns can be identified by marking. In addition, the manufacturer indicates this indicator in the technical specifications.
For example, it is known that 0.87-0.9 is the characteristic density of 15W40 engine oil at fifteen degrees. The indicator of 0.857 kg will often be with a winter mark of 10W. And about 0.85 will be the density of 5W40 engine oil.
Summer rate at twenty will be equal to 0.861 kg / l, and at fifty - 0.875 kg / l.
Recently, the most widely used lubricating fluids, which have the ability to work equally well in the summer and in winter, the so-called all-season oils. Their use greatly simplified the life of motorists who no longer need to be afraid that they will forget to change their fluid when the hot season or, conversely, the cold season sets in.
Hydrometer
To measure density, use a device called a hydrometer. This is such a float made of glass, with ballast at the bottom, a thermometer in the middle and a thin tube with a scale at the top.
The device is placed in oil for a period of three to five minutes and the readings are taken on a scale. The density of motor oil (kg / l) is indicated at a temperature of two hundred degrees. If the measurements were carried out at a different temperature, the result is adjusted according to the corresponding table in GOST.
Density measurement
To determine the properties of the lubricating fluid, its relative density is used, calculated on the basis of the ratio of the density of the oil to the density of water at a temperature of forty degrees (with equal volumes).
The density measurement is carried out as follows.
- An oil product is poured into a glass flask at a temperature of twenty degrees.
- Carefully lower the hydrometer so that it does not touch the walls of the vessel.
- After a few minutes, holding the device at eye level, make a measurement, while taking a 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 gasoline - from 910 to 930 kg / m3.
This parameter helps to compare the properties of different lubricating fluids. However, it alone cannot be used to judge the quality of the oil as a whole. For this, color, transparency of the product and other indicators are taken into account.