Engine oil knowledge that car owners should master

Help you understand the oil drum
SAE is the United StatescarThe English abbreviation of the Society of Engineers, SAE grade represents the viscosity grade of oil. SAE30 and SAE40 are single-grade oils, and SAE10W-30 and SAE15W-40 are multi-grade oils. Among them, the smaller the number in front of "W", the lower the low-temperature viscosity, and the better the protection ability of the engine during cold start; the number after "W" is the index of high temperature resistance of engine oil.
API is the English abbreviation of American Petroleum Institute, and API grade represents the classification of engine oil quality. It uses simple codes to describe the working capacity of the engine oil. API engine oil is divided into two categories: "S" series represents gasoline engine oil; "C" series represents diesel engine oil; when the letters "S" and "C" are present at the same time, it means that this engine oil is gasoline and diesel general purpose oil. . If "S" comes first, it is mainly used for gasoline engines. On the contrary, it is mainly used in diesel engines.
From "SA" to "SJ", each increment of a letter makes the performance of the oil better than the previous one, and there will be more additives used to protect the engine in the oil. The lower the letter, the higher the quality level. Most of the oil levels in international brands are above the SF level.

　　Oil brand recognition
Generally, engine oils are classified by viscosity classification and quality classification. The SAE (American Society of Automotive Engineers) classification and API (American Petroleum Institute) classification, which are widely used internationally, are the typical representatives of the two classification methods.

According to the SAE method, there are 6 kinds of oils for winter, 4 kinds of oils for summer, and 16 kinds of general-purpose oils for winter and summer. The oil grades for winter are: 0W, 5W, 10W, 15W, 20W, 25W. The symbol W represents winter. The smaller the number before W, the lower the low-temperature viscosity, the better the low-temperature fluidity, and the lower the applicable minimum temperature; Summer oil grades are: 20, 30, 40, 50. The larger the number, the higher the viscosity and the higher the applicable maximum temperature; the winter and summer general oil grades are: 5W/20, 5W/30, 5W/40, 5W/50, 10W/20, 10W/30, 10W/40, 10W/50, 15W/20, 15W/30, 15W/40, 15W/50, 20W/20, 20W/30, 20W/40, 20W/ 50. The smaller the number representing the winter part, the larger the number representing the summer part, the higher the viscosity and the larger the applicable temperature range.

According to the API quality classification method, engine oil is divided into gasoline engine oil series (namely S series) and diesel engine oil system (namely C series). The oil products of each series are arranged in alphabetical order and divided into several grades.

For engine oil imported from abroad and Hong Kong and other places, the mark on the package consists of two parts: SAE viscosity classification level and API quality classification level. It usually starts with SAE, followed by the viscosity code; while the engine oil grades classified by API quality generally omit API, and directly mark the quality grade code. For example: the label is SAEl0WSD, which means the viscosity classification is SAEl0W, and the quality star grade is API SD winter gasoline engine oil; the label is SAE30SD, which means the viscosity classification is SAE30. Summer gasoline engine oil with quality grade APISD; the label is SAEl0W-30SD (or SAEl0W/30SD), indicating that the viscosity classification is both SAEl0W and SAE30 winter and summer general gasoline engine oil, and its quality grade is API SD grade.

　　Characteristics and differences of engine oil

At present, the quality classification system of the American Petroleum Institute (APT) is the most widely used engine oil classification system. It uses simple codes to describe engine oil based on the working ability of the oil. Among them, the "S" category is used in gasoline engines, from "SA" to "SH". With each letter incremented, the performance of the engine oil will be much better than the previous one, and there will be more additives used to protect the engine in the engine oil.

Among the characteristics of engine oil, the most important point is its viscosity. For those oils that have low viscosity at low temperatures and high viscosity at high temperatures, which can ensure that the engine can be lubricated normally at any temperature, we define them as multi-grade oils. At present, the engine oils on the market are divided into mineral oil and synthetic oil, and the highest grade oil is synthetic oil.

Generally, high-end cars choose synthetic engine oil. Synthetic oil has a higher viscosity index than ordinary mineral oil, and the viscosity change caused by temperature change is small, so it can still maintain a proper viscosity under high temperature and severe cold conditions, and provide suitable protection. In addition, synthetic oil has a low tendency to produce acid and sludge due to oxidation. Under various severe operating conditions, it can provide proper lubrication and effective protection to the engine, thus having a longer service life.

The selection and use of oil can be based on the following aspects.

　Distinguish by quality

Engine oil can be divided into mineral oil and synthetic oil because of the difference of its base oil (vegetable oil is not counted because of its scarce production). The biggest difference between the two is: synthetic oil uses a wider temperature, longer service life, and higher cost; the same oil film requirements, synthetic oil can be achieved with a lower viscosity, while mineral oil needs to be used compared to synthetic oil. Only thicker viscosity can meet this requirement. In the same working environment, synthetic oil has a much longer service life than mineral oil, so the cost is higher, but after comparing the number of oil changes, it is not much higher than mineral oil. (This article does not involve semi-synthetic motor oil)

Distinguish by viscosity

　　Viscosity refers to the internal friction of fluid (including gas and liquid) when it flows, that is, flow resistance.generallylubricating oilBoth will provide the viscosity at 40 degrees Fahrenheit and 100 degrees Fahrenheit, 40 degrees is relative to the condition of the cold car, and 100 degrees is the condition of high-speed operation or traffic jam. If the viscosity is too strong, the resulting resistance will be relatively increased, so the following unfavorable factors will be produced: 1. It will affect the start of the engine when the car is cold. This will be more obvious at low temperatures. For example, in winter to enjoy the snow in the snow-capped mountains, 20W/50 is not as good as 5W/40 is easy to start; 2. Increased fuel consumption. High oil resistance is also high, which will cause higher frictional resistance to the operation of the engine's internal parts, which will increase fuel consumption; 3. Increase engine wear when starting the engine When it is not started for a period of time, the oil originally attached to the upper part will flow back to the oil pan, and the upper part lacks enough oil to protect the engine under starting conditions. If the oil viscosity is thick, the flow will be slow, so the chance of wear will increase; Fourth, if the oil viscosity is too thick, the internal resistance will be greater, and the resistance will be converted into heat, which will increase the temperature of the machine during operation.

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