What is the easiest and most practical way to distinguish whether the oil is good or bad?
It's frozen!
Get a little new oil in a sealed glass bottle and put it in the freezer compartment of the refrigerator, adjusting the temperature to minus 21°C (if the temperature outside is lower than this, leave it outdoors). After waiting for 24 hours, and then observing its traits and mobility, it is a ghost that can be seen at once. If you want to see more thoroughly and more bluntly, you can find a few more brands of oil for comparison, and you can even deliberately find a few fake oils to see the difference between real oil and fake oil after freezing.
After the oil is frozen, we mainly look at its two characteristics: turbidity and fluidity.
Let's start with turbidity.
Normal engine oil is a mixture of a variety of substances, but also absorbs a certain amount of water. After freezing, these substances will crystallize and suspend in the oil, forming an emulsion, which we look like the oil has become turbid. We take out the frozen oil and check its turbidity to roughly judge the advantages and disadvantages of the oil.
In general, the higher the turbidity of the oil after freezing, the worse the quality of the oil; the lower the turbidity, the better the quality of the oil. Some fake oils, after freezing, are even completely cloudy and opaque, and even have particles or flocculents precipitated, such oils can never be used. The big brand of real engine oil, regardless of its viscosity, is clear and transparent after freezing, and there is little difference from the normal temperature state, the turbidity is low, there is no precipitation precipitation, and no bubble formation.
Let's look at the fluidity of the oil after freezing.
Now the oil is a compound oil, such as 0W-20, 5W-30, 10W-40, etc., can meet the needs of the car in a variety of temperature conditions at the same time, of which 0W, 5W, 10W refers to the low temperature viscosity of the oil. We can roughly understand that 0W means that the minimum usable temperature of oil is below -35 °C, 5W means that the minimum usable temperature of oil is below -30 °C, 10W means that the minimum usable temperature of oil is below -25 °C, and so on. Of course, this recognition is not absolute, the actual situation is more complicated than this, some high-quality 5W oil, at -35 ° C, still has good fluidity.
In addition, there is also a parameter to measure the low temperature performance of the oil is the pour point, that is, the temperature at which the oil completely loses its fluidity. In general, the pour point of the oil is 5 to 8 °C lower than the minimum available temperature, such as the incant point of 0W oil below -42 °C, the incantation point of 5W oil below -37 °C, the incest point of 10W oil below -28 °C, and so on.
We took out the frozen oil and placed it upside down to see how fast the oil flowed. The faster the speed, the better the fluidity of the oil. The most important feature of high-quality engine oil is "low temperature is not sticky, high temperature is not thin". Maintaining good fluidity at low temperatures allows the oil to reach the lubrication surface in the shortest possible time when the engine is started, reducing engine wear as much as possible. Therefore, we can roughly think that the better the oil with low temperature fluidity, the better the quality; the lower the pour point, the better the quality.
In terms of low temperature fluidity, the fully synthetic oil is the best, its viscosity temperature characteristics are good, and it can still maintain good fluidity at very low temperatures; while the viscosity temperature characteristics of mineral oil are poor, and the fluidity is relatively poor at low temperatures. After some fake oils are frozen, they are not only highly turbid, but also have poor fluidity, and even completely solidify, and we can also use this method to roughly distinguish between real and fake oils.
On the Network, there are many ways to distinguish the advantages and disadvantages of the oil, such as instrument detection method, smell, viscosity measurement, look at packaging, etc., these methods are either too complex, or too subjective, or require a lot of experience, personally think it is not very practical. And this method of freezing, everyone can do, the identification method is simple, does not require additional costs, is more practical. Although this method can only test the low temperature performance of the oil, in general, the oil with good low temperature performance is not bad at high temperature.