Patent ID: 8759267

Claim:
A method for improving the fuel economy of large low and medium speed engines that reach surface speeds of at least about 100 mm/s and are lubricated by an engine oil by reducing the traction coefficient of the engine oil used to lubricate the engine by employing as the engine oil a lubricating oil comprised of a base oil comprising a bimodal blend of two different base oils, the first base oil being one or more oils selected from the group consisting of Group I, Group II and Group III base oils, said first base oil having a kinematic viscosity at 100° C. of from 2 to 4.2 mm 2 /s and a second base oil selected from one or more oils selected from Group IV base oils having a kinematic viscosity at 100° C. of 150 to 1200 mm 2 /s, the difference in kinematic viscosity between the first and second base oils being at least 140 mm 2 /s, the combination of the first and second base oils having a kinematic viscosity at 100° C. of 13 to 25 mm 2 /s or less wherein the improvement in fuel economy is evidenced by the traction coefficient of the engine oil employing the bimodal blend being lower than the traction coefficient of engine oils which are not bimodal or which are not bimodal to the same degree as recited or which are based on mixtures of two or more Group I base oils or mixtures of two or more Group II base oils or mixtures of Group I and Group II base oils.