ABSTRACT
The viscosity behavior of base stocks at temperatures between the cloud point, when crystals first begin to appear, and the much higher temperature at which volatility or decomposition commences is of central interest to lubricant formulators and users. Like that of most liquids, the kinematic viscosity of lube-range hydrocarbons decreases with increasing temperature. The
degree
of this decrease is important because in the majority of applications, particularly automotive, minimal change is most desirable. For example, the viscosities of naphthenic and paraffinic base stocks have very different behaviors with temperature change. These stocks, with the same viscosity of 4.0 cSt at 100
°
C, can have viscosities of 25.3 (naphthenic) and 16.8 (paraffinic) cSt at 40
°
C. Paraffinic base stocks have less viscosity variation than naphthenic stocks and therefore are preferred for many applications, particularly in the automotive area. This temperature susceptibility of viscosity depends on the base stock composition and is determined by the feedstock, the manufacturing process, and process operating conditions, and is a critical process target in manufacturing most lube base stocks.
