Is a Higher or Lower Oil Viscosity Index Better?

[DeJace]

Neither too low nor too high oil viscosity is ideal; the correct choice should be based on the maintenance manual and your actual situation. The viscosity of the oil should be selected according to the engine's own condition and the ambient temperature. If the internal parts of the engine have small gaps, a lower viscosity (thinner) oil is needed; conversely, larger gaps require a higher viscosity (thicker) oil. Additional information: 1. Although many car owners hope to have both "lower high-temperature low-shear kinematic viscosity" and "higher high-temperature high-shear kinematic viscosity," it is difficult to find oil models with very high high-temperature high-shear viscosity among low kinematic viscosity oils. For American and Japanese cars, which are moving toward greater precision under the general trend of energy conservation and environmental protection, 5W30 is often considered the ideal oil viscosity for engine warm-up. For these engines, the difference between 2.8cP and 3.5cP oil film thickness is generally negligible. 2. Besides the impact of these three viscosities on oil performance, another indicator has a killer-level influence on the oil's service life: the total base number (TBN). TBN represents the total number of alkaline elements in the oil and is an important indirect indicator of the content of cleaning and dispersing additives. Since gasoline combustion in the cylinder produces a small amount of sulfides that remain on the cylinder wall surface, and sulfides themselves are weakly acidic, manufacturers add "weakly alkaline cleaning dispersants" to the oil formulation to enhance the oil's cleaning effect. TBN is used to indicate the remaining content of cleaning dispersants in the oil, an important indicator often used to measure how much mileage is left in the oil's service life. At the same time, the rate of decline in TBN can also be used to assess combustion quality. Those oils that need to be replaced every 5,000 kilometers generally refer to high-viscosity mineral oils. From this, it is evident how significant the advantages of full synthetic oils are!