The ability of engine oil to lubricate effectively is primarily influenced by its viscosity. Viscosity is a measure of the oil's resistance to flow and deformation, which is critical in maintaining an effective lubricant film between moving parts in an engine.
When an oil has an appropriate viscosity, it can create a sufficient layer between surfaces, reducing friction and wear. If the viscosity is too low, the oil may not provide adequate protection at high temperatures or under pressure, leading to increased engine wear or failure. Conversely, if the viscosity is too high, the oil may not flow easily enough to reach all the necessary components, which can also result in insufficient lubrication.
While additives do enhance the performance of engine oil and can improve its ability to lubricate by providing additional properties (like detergents, anti-wear agents, or viscosity index improvers), they work in conjunction with the base oil's viscosity. The color of the oil and its density have less direct impact on its lubricating ability. Color can indicate the presence of contaminants or degradation, while density relates more to the oil's formulation and isn't a direct factor in lubrication performance. Thus, viscosity is the primary property that governs the lubrication capability of engine oil.