Difference in viscosity

What you are referring to is likely the viscosity of the lubricant. The apparent viscosity represents the viscosity at low temperatures during startup, while the dynamic viscosity at low temperatures can serve as an indicator of whether the engine will be able to start smoothly under such conditions. The dynamic viscosity of lubricants at low temperatures is determined through a cold start simulation test (CCS). This test simulates the conditions under which an engine’s cylinder liner-piston assembly starts up in cold conditions, and it has a good correlation with the actual cold start process of the engine. Under the same low-temperature conditions, the lower the viscosity value measured, the easier it is to start the system, and the better the protection provided. The low-temperature dynamic viscosity of the engine oil is too high, resulting in an excessive torque when the crankshaft rotates; this prevents the engine from reaching its specified minimum speed, making it difficult to start the engine ； Or it has been started, but due to the high viscosity, it cannot provide effective lubrication, resulting in severe wear of the components. The ratio of the dynamic viscosity η of a fluid to its density ρ at the same temperature is called the kinematic viscosity. It represents the measure of the flow resistance of that fluid under the effect of gravity. In the International System of Units (SI), the unit of kinematic viscosity is m2/s. Previously, centistokes (cSt) were commonly used as the unit for kinematic viscosity; 1 cSt equals 10-6 m2/s (that is, 1 cSt = 1 mm2/s)