Why do cars use synthetic oil? Does the engine need to be cleaned before changing to full synthetic oil?

Automobile motor oil is a kind of oil used for engine lubrication. There are full synthetic motor oil, semi-synthetic motor oil and mineral oil. It is generally recommended to use full synthetic motor oil. Why is that?

Why do cars use synthetic motor oil?

The main reason is that synthetic motor oil has better lubrication and protection properties. Compared with mineral oil, synthetic motor oil has a more stable molecular structure, strong antioxidant ability, better low-temperature fluidity, good oil viscosity stability, is less affected by temperature, has better cleanliness, and stronger high-temperature shear resistance, making it the best choice for engine maintenance.

Moreover, turbocharged engines are now used in large quantities, and ordinary mineral oil cannot meet the lubrication needs of turbocharged engines. Because during the operation of a turbocharged engine, the internal friction and combustion temperature of the engine are higher than those of a naturally aspirated engine, and the turbocharger itself also requires higher lubrication, so turbocharged engines can only be maintained using synthetic motor oil.

Does the engine need to be cleaned before changing to full synthetic oil?

No matter what brand or type of engine oil you change, you can replace it directly without cleaning.

The biggest difference between semi-synthetic motor oil and fully synthetic motor oil lies in the base oil and additives, and the selling prices are also different.

Although the formulas of different brands and types of engine oil are different, they are all compatible with each other. And even if you clean it, it will not work because there will always be some engine oil left inside the engine. You can drain the previous engine oil first.

What does SM mean on synthetic motor oil?

Engine oils are classified according to SAE and API standards. The API-classified engine oils are represented by S and another letter. The S series represents gasoline engine oils, and M represents the grade. The grades are arranged in alphabetical order, and the higher the grade, the better. For example, SN grade is better than SM grade.

API SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, SN, in this order, the quality of engine oil gets better and better.

SM grade oils have better oxidation resistance and deposit control, better anti-wear protection and better low temperature fluidity.