为什么换完机油后发动机的声音更大了？
Why does the engine sound louder after changing the oil?
1.机油过量
1. Excessive engine oil
机油加注也是有标准的，并非是越多越好，如果机油加注量过多，对曲轴旋转工作产生更大的阻力，从而影响动力输出，增加油耗。进入燃烧室的机油量大大增加，使燃烧室内积碳增多，增加了活塞运动阻力，使发动机功率下降。同时也会造成燃烧室空燃比发生变化，增加爆震的几率，噪音也会随之加大。
There is also a standard for oil filling, not the more the better. If the oil filling is too much, it will produce greater resistance to the rotation of the crankshaft, thus affecting the power output and increasing fuel consumption. The amount of oil entering the combustion chamber is greatly increased, which increases the carbon deposition in the combustion chamber, increases the piston movement resistance and reduces the engine power. At the same time, it will also cause the air-fuel ratio of the combustion chamber to change, increase the probability of detonation and increase the noise.
2.中度积碳
2. Moderate carbon deposition
老机油越用越稀，积碳越来越多。机油稀了容易窜机油，造成积碳越来越多。当换上新机油时，发动机不能适应机油粘度，可能会拉高转速，进而造成发动机噪音大。建议用高标号汽油开高转速，建议保持开2500转以上开一箱高标号油应该就有改善，当然也可以进行预防性清洗。
The old engine oil is thinner and thinner, and carbon deposits are more and more. When the engine oil is thin, it is easy to channelle the engine oil, resulting in more and more carbon deposition. When the engine is replaced with new oil, the engine cannot adapt to the oil viscosity, which may increase the speed and cause loud engine noise. It is recommended to use high-grade gasoline to drive at high speed. It is recommended to keep driving more than 2500 rpm. Opening a box of high-grade oil should be improved. Of course, preventive cleaning can also be carried out.
3.机油粘度要适合
3. The oil viscosity shall be suitable
不同等级的机油有着不同的特性，其低温启动性和高温的抗磨、附着性也有着不同的表现。机油的黏度与温度呈反比的关系，当发动机冷态时，机油黏度较高，若选用的机油较稠，便会给启动马达、电瓶等增加额外的损耗。但若机油过稀，在高温工作下则难以形成足够的保护膜而引起润滑不足，导致机件加大磨损。如果车辆手册建议5W-30，而车主要用5W-40的那发动机噪音变大，那么车主就需要注意了。建议选机油建议是车辆手册推荐的标号。
Different grades of engine oils have different characteristics, and their low-temperature start-up and high-temperature anti-wear and adhesion also have different performances. The viscosity of the engine oil is inversely proportional to the temperature. When the engine is cold, the viscosity of the engine oil is high. If the selected engine oil is thick, additional losses will be added to the starting motor and battery. However, if the engine oil is too thin, it is difficult to form sufficient protective film under high temperature operation, resulting in insufficient lubrication and increased wear of parts. If the vehicle manual recommends 5W-30 and the vehicle mainly uses 5W-40, the engine noise becomes louder, then the owner needs to pay attention. The recommended engine oil is the grade recommended in the vehicle manual.
4.机油混加
4. Oil mixing
这种情况也比较常见，由于不同品牌用的技术配方不同，可能会产生不良化学反应，改变其本身自有的特性，从而对发动机造成磨损，噪音增加。建议车友们建议不要混加机油，尽量使用同一品牌的机油。如遇特殊情况更换不同品牌机油，建议使用同标号机油。
This situation is also common. Due to different technical formulas used by different brands, adverse chemical reactions may occur and their own characteristics may be changed, resulting in engine wear and increased noise. It is recommended that motorists do not mix engine oil and try to use the same brand of engine oil. In case of special circumstances, it is recommended to replace oil of different brands with oil of the same grade.
5.遇到假机油
5. False engine oil
这种情况也是很有可能出现的，由于新手司机在给自己的爱车做保养时，加入了劣质的机油。由于“假”机油它的抗磨、清洁、润滑保护等性能都非常差，导致发动机压力过大，从而磨损加剧、噪声加大。作为消费者，对相关的防伪知识要知道一些，不能只道听途说，要懂得如何辨别机油的真伪。
This situation is also likely to occur, because novice drivers add inferior engine oil when maintaining their car. Due to the poor anti-wear, cleaning and lubrication protection of "fake" engine oil, the engine pressure is too high, resulting in increased wear and noise. As consumers, they should know some relevant anti-counterfeiting knowledge, not just hearsay, but how to distinguish the authenticity of engine oil.
6.冷车声音大正常
6. The sound of cold car is loud and normal
冷车状态机油大部分都回流到油底壳，这时候发动机内部器件缺少润滑，冷车启动的时候发动机温度还会变低，机油的润滑性能也达不到好的状态，加上发动机预热转速的原因会造成噪音偏大，但热车后噪音转速又会降下来了，这个是正常情况。如果热车后没有恢复正常，建议大家去检查一下。
When the engine is cold, most of the engine oil flows back to the oil pan. At this time, the internal components of the engine are lack of lubrication. When the engine is cold, the engine temperature will become lower, and the lubrication performance of the engine oil can not reach a good state. In addition, due to the preheating speed of the engine, the noise will be too high, but the noise speed will drop again after the hot car. This is a normal situation. If it doesn't return to normal after hot driving, I suggest you check it.
7.心理作用
7. Psychological function
这个应该是占大多数，人的听力在不同的环境是有误差的，单凭耳朵是不能判定声音变大的，建议用分贝仪测量。从油品粘度的技术角度分析，5W-20、5W-30的机油在市区行驶中噪音会稍微大些，在高速正常行驶，噪音会稍小些。5W-40、5W-50的油品在市区行驶中噪音会稍小些，上了高速正常行驶，噪音会稍大些。
This should account for the majority. People's hearing has errors in differe