Abstract: The paper reveals a phenomenon that the pour point of mixed base oil is below the pour point of each component of the mixture. The phenomenon is obvious when naphthenic base oil is mixed with paraffinic base oil. Pour point and other physicochemical properties of mixtures with different naphthenic base oil and paraffinic base oil ratios and component were all analyzed. A hypothesis for the phenomenon was proposed based on the carbon structures of base oils and mechanism of pour point depressant, combined with the analysis of oil properties. The obvious degree of the phenomenon depends on the types, the pour point difference and the viscosity (100 ℃) difference of the two components. Tests show that the influence of three factors on the low temperature performance is in turn. The greater the solidification mode difference, the closer the pour point and viscosity (100 ℃) of two components, the more obvious of the phenomenon is. KN4010 is naphthenic base oil and HVIP8 is paraffinic base oil. The pour points of the two component are both -24 ℃, their viscosities of 100 ℃ are close, the pour point of the mixed oil of two component can be -42 ℃.

Key words: pour point, pour point depressant , naphthenic base oil, paraffinic base oil