The correct selection of lubricants in summer

In summer, not only the human body will have various adverse reactions, but also the car. Today, Xiao Bian shares with you one of the things you need to pay attention to in summer car - Lubricating Oil.

The role of lubricants

The heat generated by the friction between the engine's various motion bearing surfaces is second only to the heat of the engine cylinder's combustion, while the lubricant oil takes away the heat by pressure lubrication, thus ensuring the normal operation of the friction surface. These heated lubricating oils return to the oil sump through the oil gallery for cooling. From the engine's structural point of view, the oil pan is located at the bottom of the engine, and it is exposed to the air. Generally, it is made of a material with good thermal conductivity, and the lubricant is air-cooled through it. The cooled lubricant is then sent to the lubricating surface. The viscosity of the lubricating oil is very important for protecting the engine. Only when the lubricating oil has sufficient viscosity can it be ensured that the oil film can be maintained between the engine parts at various temperatures so as to protect the normal operation of the engine.

Why does the high temperature in summer pay attention to the viscosity of the lubricant?

First, when the engine is running at high temperatures, the oxidation stability of the lubricating oil deteriorates, exacerbating its thermal decomposition, oxidation, and polymerization. At the same time, the dust in the dry air and the moisture in the moist air enter the engine oil pan through the air intake system and the crankcase vent to contaminate the lubricating oil, so the lubricating oil is easily deteriorated.

Second, the viscosity of lubricating oil changes with increasing temperature, that is, when the lubricating oil is heated, the viscosity decreases, which may cause the lubricating oil to be consumed too quickly.

Third, the engine runs at high temperatures, the thermal expansion of metal parts is large, and the normal fit gap between parts becomes smaller, and the wear becomes worse. At the same time, high-temperature running engines adhere to carbon deposits and colloidal substances on the top of the piston, the wall of the combustion chamber, the valve head, etc., which deteriorates the thermal properties of metal parts and accelerates the damage of the mechanical parts. In addition, due to the overheating of the engine, the oil becomes thinner, the oil pressure is reduced, the lubricant film is not easy to form, and the wear of the parts is also accelerated.

Reasonable choice of lubricant viscosity

Lubricants are generally classified according to their viscosity and quality. There are 6 kinds of oil in winter, 4 kinds of oil in summer, and 16 types of oil in winter and summer. Lubricant brands in summer are 20, 30, 40, and 50 respectively. The larger the number, the greater the viscosity and the higher the applicable temperature. For example: SAE15W-40, SAE5W-40. The number behind "W" indicates the index of the high temperature resistance of the lubricant. The larger the value, the better the protection performance of the lubricant at high temperature. In general, consumers in most parts of the country from April to September can choose summer lubricants of 15W-40 or 10W-40.

At the same time, for high-end cars, it is recommended to select high-quality synthetic lubricants as much as possible. Compared with common mineral oils, synthetic oils have little change in viscosity with temperature and can maintain proper viscosity at high temperatures.

Lubricant is not as good as viscosity

Although the viscosity of lubricating oil is very important, the owner should abandon the erroneous recognition that “the higher the viscosity is, the better” and select the appropriate quality level according to the actual conditions of the vehicle, the temperature, and the condition of the engine. Only in the case of a large gap between the engine parts of the car, choose a lubricant with a large viscosity.

The use of excessively viscous lubricants will have at least two disadvantages:

First of all, when the viscosity is too high above the level that affects the start of the engine, it is very likely to cause severe wear on the engine when it starts. Because the viscosity of the lubricant is too large, the flow is slow and the hydraulic pressure is high, but the amount of lubricant passing through is not large, and it cannot be added to the friction surface in time. The circulation speed of the oil also becomes slower, and its cooling and heat dissipation effects become very poor, resulting in engine overheating. Since the circulation speed of the lubricant is slow, the number of passages of the lubricant filter is also reduced, so that it is difficult to timely remove the worn metal shavings, carbon particles, and dust from the friction surface.

Another drawback of using excessively viscous lubricating oils is energy consumption. As the viscosity is too large, the friction between the friction surfaces of the parts increases, and in order to overcome the increased friction, more fuel is consumed, resulting in a huge waste of energy. It is understood that the low viscosity of lubricants has become an international trend in foreign countries. In China, although there is no mandatory requirement for energy saving of lubricants, low viscosity will be the future trend.

Summary: The high temperatures in the summer are also a matter of caution for the choice of lubricants. It is necessary to choose a lubricant with a large viscosity, but also to abandon the misconception that the higher the viscosity, the better. The choice is not good, if it is serious, it will damage the engine.

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