When going to maintain and release the old engine oil, the maintenance master will often say that the engine oil is very dark and indeed dirty. Let the owner feel that this oil change is more worthwhile, and the oil is so dirty. However, does the fact that the oil turns black is a sign that it is time to change? The answer is no, the freshly changed engine oil runs hundreds of kilometers, but it actually looks black. This is because the black color is more obvious and there is no color difference, like two drops of ink in a glass of water, the whole glass of water is black, but there is not much ink. Therefore, it is not possible to determine whether the oil should be changed based on color alone.
Why does engine oil turn black? This is actually a function of the engine oil, which has an additive called a detergent and dispersant. It absorbs all the dirt and disperses it into the oil to prevent deposits from forming in the oil ducts for a long time, clogging the oil passages and causing the oil pressure to be insufficient. A common dirty thing is carbon deposits from combustion. There is often a lot of carbon deposits on the top of the combustion chamber pistons, but there is no carbon deposit on the cylinder wall, even in an old car, the cylinder wall is very bright and smooth when the cylinder is opened. This is because when the piston is running upwards, the piston rings coat the cylinder walls with a layer of oil, and when the piston runs downwards, this layer of oil is scraped clean by the piston rings.
If there is a small amount of carbon deposits on the cylinder wall, it will be carried to the oil to disperse and dissolve. The main reason why we see the oil is black is because of the dissolved carbon deposits. It doesn't take much carbon to deposit, just a small amount of carbon will make the oil take on a black color, just like dripping ink into water, just one or two drops can make the whole glass of water black. In addition, some iron filings and the resulting cement from the wear and tear of the engine will be dispersed into the oil, and they will also appear black. If the oil is dirty, it will turn black, and if it is dirty, it will also be black, and the degree of blackness is difficult to see with the naked eye, so it cannot be said that the oil should be replaced if it is black. Although the oil has become black, it is only a change in color, and its performance does not necessarily decrease. The lubrication conditions required for engine operation can still be achieved, so the oil blackening can only be used as a simple reference.
The life of the engine oil is affected by the engine running time, the speed of the engine and the load. The longer the engine runs and the more load it bears, the more severe its life decays. Because we can't record the running time and various operating conditions, it is reasonable to refer to the number of kilometers for oil change. According to the manufacturer's suggestion, it is required to replace as many kilometers as possible. If your car conditions are different from most people's, for example, this car travels a lot and spends most of its time on the highway. Indicating that the car is in good working condition, the oil change interval should be extended, assuming that the manufacturer recommends 5000 kilometers to change the oil, this working condition should be 8000 kilometers and then replaced. If you often drive in traffic jams, the vehicle has been driving at a low speed, accelerating and decelerating repeatedly, or driving yourself fiercely and often driving violently. In both cases, the oil change interval should be shortened, or it should be replaced immediately after 5,000 kilometers without delay.
Nowadays, many cars have an oil life display, which is more accurate, it is calculated comprehensively according to various factors such as engine running time, kilometers driven, operating conditions, etc., which is relatively reliable. Generally, when the oil life is less than 20%, it can be considered to be replaced, and it must be replaced when it is less than 10%. In addition, an experienced repairman can also be determined by manually checking the oil. Pull out the dipstick to see if the color is already very dark, and then smell the smell to determine whether there is a sour smell, if there is a sour smell, it means that the oil has deteriorated and must be replaced immediately. Finally, drop a drop into your hand, use the method of hand twisting, feel whether there are a lot of impurities, and use these methods to determine whether the oil should be changed.
Some people also say whether it is necessary to clean the oil duct before changing the oil, so whether it will be replaced more thoroughly. Generally, there is no need to clean, the oil itself has a cleaning and dispersant, for the vehicle that changes the oil on time, there is no sludge and impurities in the oil passage, all of them are in the oil, and no additional cleaning is required. Unless you often postpone the oil change, or this time it has exceeded many kilometers, the original 5000 should have changed the oil, but the result is 10000 kilometers before the change, you can clean it first. Other vehicles with normal oil changes do not need to be cleaned, and there is no effect after washing.