Yorulmaz, YavuzUslu, Hasan2015-04-072015-04-072009Journal of Science and Technology 3 (1), 2009, 127 - 1391307-3818The Viscosity-Gravity constant (VGC) can be more useful for predicting viscosities of lubricating oil blends by combining the VGC with a term to reflect the paraffinic or napthenic nature of the oils as compared to other theoretical and semi-theoretical methods found in literature. In this work, the combination of VGC and paraffin content of oil is used to predict viscosity at 100 oF (37.8 oC) and 210 oF (98.9 oC). The viscosities are among the important properties standardized by the American Society for Testing Materials (ASTM) and by the Institute of Petroleum (IP) for quality control of finished lubricating oil products. The viscosities were found to have a strong correlation with composition and VGC. Therefore, oil composition was considered a correlating parameter. The equations were derived from experimental data and no theoretically derived equations of similar nature were found in the literature for comparison purposes. For oils of the same viscosity, a low specific gravity (high API) indicates a paraffinic oil while high specific gravity (low API) indicates a napthenic oil. From the concept of viscosi-ty-gravity constant the higher VGC indicates a more napthenic oil and, conversely the lower VGC indicates a more paraffinic oil. Also a higher VGC suggets an oil will have a greater rate of viscosity change with a change in temperature.enViscosityVGCAPIParafınNaptheneArticle