Switching to low viscosity oil may really save fuel.
First of all, we should know that the "20" and "30" in the oil labels 5W-20 and 5W-30 refer to the viscosity of the oil.
Viscosity is to judge the fluidity of a flowable substance. The greater the viscosity, the worse the fluidity; The smaller the viscosity, the better the fluidity. Just like honey and water, honey has a high viscosity and is more difficult to pour out in a bottle than water.
The engine is lubricated by engine oil, and the engine oil needs enough viscosity to achieve lubrication and protection. The high viscosity of engine oil will increase the resistance of the oil pump and increase the energy loss when the engine starts.
It's like mixing water and honey with a stick. It's easy to stir water, but it's a little hard to stir honey.
Many big brands are pursuing low viscosity engine oil, because in terms of engine technology, manufacturers are also constantly pursuing smaller engines. The smaller the engine, the finer the parts.
In the past, domestic cars mainly used 5W-40 engine oil. With the increasing demand for the fuel consumption limit of passenger cars and the call for various energy-saving measures, many automobile manufacturers began to use 5W-30 engine oil as one of the measures to reduce the fuel consumption of the whole vehicle.
In Jin Hailing, Xiang Hui, Jin Xianyang and others' paper "Influence of Low Viscosity Engine Oil on Energy Saving of Engine/Vehicle", it is mentioned that low viscosity engine oil can reduce the friction loss of engine. The lower the temperature, the more obvious the effect of low viscosity engine oil on reducing the friction loss of engine, and it can also improve the fuel economy of vehicle.
In addition, low viscosity engine oil can obviously reduce carbon dioxide emissions, which is one of the reasons for advocating low viscosity engine oil.
Low viscosity oil will increase engine losses,
The lubricating effect of oil depends on the oil film it forms. If the oil film thickness is not enough, there is no way to separate the metal surfaces of the parts, so there is no? The lubrication effect is improved.
The lower the viscosity of engine oil, the thinner the oil film, which is easy to break when flowing between parts, resulting in dry friction between engine parts.
For example, maintenance workers often work with gloves on. If the gloves are too thin, they will be easily cut at work.
The recommended engine oil model written in the automobile factory manual is the lowest viscosity grade.
For example, it is recommended to use 5W-30 engine oil, but at this time, if you switch to 5W-20 engine oil, dry friction may occur when the engine is working, which will not only save fuel, but also increase energy loss and even damage the engine.
Low viscosity engine oil will increase evaporation loss.
The viscosity of the oil will change with the temperature. With the increase of temperature, the viscosity of oil will become lower. Chocolate, for example, is solid at room temperature and will melt into liquid when heated.
The lubrication system of an engine consists of many parts, and the working temperatures of different parts are different. Moreover, the overall temperature of the engine is different under different working conditions.
Feng Bo's "Research on Testing Method of Engine Oil's Low Temperature Performance" mentioned that the temperature of different components can reach between 400℃ and 600℃, and the engine starting temperature may sometimes be as low as 40℃.
Therefore, when the oil works inside the engine, the viscosity will change. In Sun Zhiqiang's research on the lubrication risk of ultra-low viscosity engine oil, it is mentioned that when the kinematic viscosity of engine oil decreases gradually, the evaporation loss of engine oil will also increase gradually.
This will affect the combustion chamber of the engine, resulting in incomplete fuel combustion. Therefore, the use of low viscosity engine oil will increase the evaporation of engine oil, which is not necessarily more fuel-efficient.
The sealability of low viscosity engine oil will be reduced.
When the engine is working, the main lubricating part of the engine oil is the bearing, which is always running. In order to keep the lubricating oil film intact and the bearings cool, the lubricating oil must be replenished constantly, so the oil actually flows continuously inside the engine.
It is mentioned in "Research on Direct Resource Utilization and Modified Graded Utilization of Waste Engine Oil" that engine oil also has the function of sealing and leakage prevention.
Because there are certain gaps between engine parts, such as between cylinder and piston, between valve and valve seat, between piston ring and ring groove, engine oil can form sealing rings in these gaps, reducing gas leakage and preventing external pollutants from entering.
In Sun Zhiqiang's research on the lubrication risk of ultra-low viscosity engine oil, it is also mentioned that when the kinematic viscosity of engine oil decreases gradually, the sealing performance of engine oil will decrease, and fuel and exhaust gas may enter the crankcase, polluting and diluting the engine oil.
Low viscosity engine oil is difficult to develop and expensive.
The development of low viscosity engine oil has high technical content and high development cost, and there are still many problems to be overcome. At present, the low viscosity engine oils on the market are mainly 5W-20 and 5W-30, and the lower viscosity engine oils are more expensive. Economically speaking, low viscosity engine oil can save fuel, but whether it saves money needs to be considered.
If a friend wants to change the oil with lower viscosity, first look at the instruction manual of his car, which indicates the recommended oil model.
If the oil grade being used is higher than the recommended grade, it can be changed to a lower grade.
If the amount of oil being used is consistent with the recommended amount, it is not recommended to change it to a lower amount. If you want to improve the working condition of the engine, you can try to change a better quality oil.