This usually causes higher wear. Oxidation measures gums, varnishes and oxidation products. High oxidation from oil used too hot or too long can leave sludge and varnish deposits and thicken the oil. Total base number generally indicates the acid-neutralizing capacity still in the lubricant. Total solids include ash, carbon, lead salts from gasoline engines, and oil oxidation.
Viscosity is a measure of an oil's resistance to flow.
Oil may thin due to shear in multi-viscosity oils or by dilution with fuel. Oil may thicken from oxidation when run too long or too hot. Oil also may thicken from contamination by antifreeze, sugar and other materials . Thrust washers, bearings and pistons are made of this metal. High readings can be from piston skirt scuffing, excessive ring groove wear, broken thrust washers, etc.