VII come in various shapes, sizes, and quality levels, with larger molecules generally being better thickeners but more prone to breaking, affecting shear stability. Thickening Efficiency (TE) measures the increase in kinematic viscosity at 100°C after adding a specific amount of polymer. Higher TE indicates more effective thickening, influenced by polymer chemistry and molecular weight.
Mineral-based multigrade oils require more VII to meet viscosity requirements, but these additives wear out over time, reducing the oil’s viscosity and necessitating more frequent changes. In contrast, synthetic oils have higher native viscosity indices, needing less or no VII, which helps maintain viscosity longer and reduces the need for frequent changes.