difference between oil viscosity
Viscosity (a fluid's resistance to flow) is rated at 0Â° F (represented by the number preceding the W [for Winter]) and at 212Â° F (represented by the second number in the viscosity designation). So 10W-30 oil has less viscosity when cold and hot than does 20W-50. Motor oil thins as it heats and thickens as it cools.So, with the right additives to help it resist thinning too much, an oil can be rated for one viscosity when cold, another when hot.or example, oil tends to lose viscosity from shear, the sliding motion between close-fitted metal surfaces of moving parts such as bearings. So resistance to viscosity loss (shear stability) is necessary to enable the oil to maintain the lubricating film between those parts.