Who says you have to use oil with a higher viscosity in the summer?

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Abstract: Summer has arrived, and for car owners, it is also an important season for vehicle maintenance. The weather is hot, and there is a saying that oil with a higher viscosity should be used in summer. Is this statement correct? Summer has arrived, and for car owners, it is also an important season for vehicle maintenance. The weather is hot, and there is a saying that oil with a higher viscosity should be used in summer. Is this statement correct? This claim was reasonable in the past, but it is incorrect now. Why? This problem arises because oil technology has advanced, but the knowledge regarding its use has not been updated in a timely manner. Engine oil is a type of lubricant; as the temperature rises, the viscosity of lubricants decreases, causing the oil to become thinner. As the temperature drops, the viscosity of the lubricating oil increases; the oil becomes thicker and its fluidity decreases. Just like cooking oil, when the temperature drops to a certain level, its flow can even come to a halt. This can result in poor flow of oil when starting the engine in cold weather, leading to engine damage. The phenomenon in which the viscosity of lubricating oil changes with temperature is called the viscosity-temperature behavior of lubricating oil, and it is expressed by the viscosity index. In the past, since refining technology was not as advanced as it is today, the performance of engine oils was not as mature as it is now. Lubricants used in the past contained many impurities such as paraffin, which made it easier for the oil to stop flowing at low temperatures. With the advancement of refining technology, engine oils are refined to a much higher standard than before, allowing them to be used at lower temperatures. Furthermore, the widespread use of synthetic engine oils (PAO) has also significantly improved the performance of these oils. PAO can tolerate a wide range of temperature changes, remains fluid at temperatures close to -40°C, and also possesses good high-temperature stability. In the past, oil viscosity grades were single-level, such as SAE10W, SAE30, etc. In winter, due to the lower temperatures, oil with a lower viscosity is used to ensure better fluidity. In summer, there is no issue with cold starting, so an oil with a higher viscosity can be used. The use of oils with different viscosities depending on the driving conditions and season is mainly due to past oil technologies. With the advancement of engine oil technology, multi-grade oils have emerged, such as SAE0W-40 and SAE5W-30; these differ from single-grade oils in that multi-grade oils are indicated by two numbers, while single-grade oils are indicated by just one number. Multi-grade oils take into account the issue of cold starts in winter, and their low-temperature performance has been tested. When choosing engine oil, users should select the oil’s low-temperature grade based on the lowest winter temperatures in their area. Most engine oils these days are multi-grade oils. To help users choose the appropriate viscosity for their needs, oil manufacturers specify viscosity grades (the internationally standard for viscosity grades of engine oils is the SAE viscosity scale), which facilitates our selection process. For multi-grade oils, W stands for winter; the number to the left of W indicates the low-temperature performance, with lower numbers meaning that the oil can be used at lower temperatures. For example, SAE5W-30 can be used at lower temperatures than SAE10W-30. The number on the right side of W represents the viscosity of the engine oil at the operating temperature of the engine; it is generally measured at 100°C, which is considered to be the temperature at which the engine operates, and thus the viscosity required when the engine is running. For a given piece of equipment, the viscosity required during operation is determined by the equipment manufacturer through scientific calculations, and users should not change it arbitrarily. In other words, the number on the right side of W is determined based on the operating temperature of the engine, not the ambient temperature in summer. Although temperatures are high in summer, it is important to distinguish between the ambient temperature and the operating temperature of the engine; they should not be conflated. So, what is the correct way to choose oil? Check your car’s user manual, which contains instructions on how to choose the right oil. Users should select engine oil according to the manufacturer’s requirements. For users in the northern regions, determine the low-temperature grade of the oil based on the local minimum temperature, which is the numerical value to the left of the W. Ensure that the minimum operating temperature allowed for the engine oil is lower than the lowest winter temperatures in your area. As for the number on the right side of W, it represents the viscosity grade required when the engine is in operation, and it should be selected in accordance with the regulations.