The lubricating oil of the present invention has a viscosity suitable for use in a diesel engine and includes at least one functionalized olefin polymer, and at least one zinc dialkyl dithiophosphate (ZDDP). The ZDDP is made from a mixture of primary alcohols or a mixture of primary and secondary alcohols, wherein the lubricant has a high boundary film value greater than or equal to 15, and preferably greater than 60, as measured by using a High Frequency Reciprocating Rig (HFRR).