“Black oil means good cleaning effect”, is it true?

On the Internet, I often see some car owners say that when they change the oil, they find that the old oil is particularly black, and they are worried about whether there is a problem. Then someone said, “the oil is black, which means that the cleaning ability of the oil is good, and the impurities are dissolved. If the oil is not black, it’s not normal. The dirty things are left in the engine. ”

is it true that the old engine oil is black? I don’t think so. Although oil has a cleaning effect, we still need to consider an important issue, that is: is there really so much dirt in the engine? It’s like washing your face. After washing your face, the water may be too clean, or you may not be dirty. But the muddy face after washing can definitely prove that the face is too dirty.

oil discoloration and oil blackening are two states. Generally speaking, after adding new oil to the engine, it will gradually change color and become darker and darker. And then it starts to turn black. Generally speaking, oil discoloration is mainly related to the following situations:

during the working process of the engine, the fuel can not be completely burned all the time, and some combustion products are always produced. Most of these substances are discharged with the exhaust gas, but a small part will adhere to the cylinder wall and be dissolved by the oil lubricated the cylinder wall. There is also a part of the combustion products with the cylinder blowby into the crankcase, in the crankcase dissolved in oil.

it is impossible for the air filter to completely filter out the dust in the air. Some dust with small diameter can easily break through the obstruction of the air filter. Most of these dust particles enter the cylinder with air and carbonize at the high temperature of combustion. Some of them are discharged with exhaust gas, and the other part is attached to the cylinder wall and dissolved by oil.

engine oil itself is composed of base oil and many additives. When the engine is working, the temperature of many lubricating surfaces is very high. The engine oil continuously experiences high temperature and high pressure. After a long time of use, some components in the oil will be oxidized, resulting in color deepening.

generally speaking, the color of the oil discharged during the specified maintenance period is much heavier than that of the new oil, but it is not completely black. It’s just that it looks very dark after being put in the oil pan due to the reflection. If you dip a tissue in old oil, you can see that the color is not black. In most cases, the oil discharged during regular oil change is almost the color shown in the above figure, which can transmit light, but the color is obviously increased. But it’s not really a dark group.

needless to say, there are a lot of fake oil now. If the substandard fake oil is added, the oil will not only turn black quickly, but also cause a lot of sludge in the engine.

the picture above shows that my new car ran a thousand kilometers of oil. It was the first maintenance date, but the mileage was not reached. However, the manufacturer requested that the first one come first, and the 4S store urged me every day, so I went to do the first service. As a result, the changed oil looked distressed.

many manufacturers require an oil change of 5000 km, but many car owners think it is too wasteful, so they will deliberately extend the oil change interval. This will generally not cause any engine problems. After all, the maintenance mileage of the manufacturer must be relatively conservative, leaving some room for it. In addition, our family car usually rarely uses high power output, so the lubrication is not so harsh. So there’s no obvious effect. However, it is easy to cause the oil to turn black. As the service time increases, more combustion products will be dissolved in the oil, and the oil will continue to oxidize, resulting in the blackening of the old oil.

this principle is very simple. When the engine is working, the oil will continuously dissolve some impurities. The less the oil is, the greater the concentration of impurities dissolved in the oil is, and the more likely it is to turn black. Just like washing clothes, the more water, the lower the turbidity. On the contrary, the less water, the more turbid the water after washing.

now, with the emission upgrading, the national sixth gasoline will be fully promoted. The cleanliness requirements of national sixth gasoline are higher, and the heavy components are further reduced. This is conducive to promote the full combustion of gasoline and reduce the formation of combustion particles. However, some substandard gasoline can not meet this condition, which may lead to insufficient combustion under some working conditions, increase the emission of particulate matter, and cause the engine oil to turn black faster.

for a gasoline engine, under normal circumstances, the ECU injects as much oil as it enters, so as to ensure that the oil entering the cylinder can be completely burned. The engine ECU uses various sensors to judge the air intake, control the fuel injection and control the ignition. If the signal of these sensors is abnormal or the engine related parts are abnormal, it may lead to abnormal air-fuel ratio. At this time, it is easy to lead to deterioration of engine combustion conditions, produce a large number of particles, and cause the oil to turn black.

if the air filter is too dirty, deformed or not installed in place, the filtering effect may become worse. At this time, the dust particles in the air inlet will increase, which will cause the oil to turn black quickly. I have a deep understanding of this point. When changing the air filter, because the design position of the air filter cover was very awkward, a gap was left after the air filter was installed. After driving for several thousand kilometers, the oil released when changing the engine oil was almost the same as that of the oil. It was black and thick. At that time, I thought there was something wrong with the engine. As a result, a lot of dust was found at the bottom of the air filter box when removing the air filter. After inspection, it was found that the cover of the air filter was not stuck in place.

basically, these are the reasons why engine oil turns black. Here I want to tell you: don’t just think that black oil is strong cleaning ability, you should know that the normal maintenance of the engine may not have so much dirt, so that the oil is so black.

so when you find that the old oil has become particularly black, you should consider whether the oil has been used too long? Is there too little oil? Is there something wrong with the gasoline? Is the quality of oil filter element poor? Should the air filter be replaced? Or there is a problem with the oil used? Then make improvements to these problems, such as selecting a better oil filter element, changing the air filter frequently, filling oil at regular gas stations, and regularly checking the oil quantity. If it is insufficient, timely replenish and change the oil according to the specified time interval. If the oil is still particularly black after targeted improvement, it is necessary to consider whether there are other problems with the engine.