Viscosity is responsible for creating a protecting film so that heat, generated in the engine does not cause friction that damages key parts such as bearings and cylinders. But when engine oils are exposed to temperature extremes, their viscosity varies as a result. This change in viscosity is detrimental to the overall performance of the oil, as a constant viscosity is ideal.
DSM's Viscosity Index Improvers (VIIs) reduce this change in viscosity as a function of temperature, allowing the oil to continue to protect the engine at high temperature, while maintaining a low enough viscosity at low temperatures to allow the engine to start and the oil to pump.
