Lubricating oil compositions with resistance to engine deposit and varnish formation

A process of improving resistance to engine deposits of an engine oil, the process comprising incorporating an amount of one or more zinc dialkyl dithiophosphates (ZDDP compounds) and an amount of one or more viscosity modifiers, wherein an amount of phosphorus (P) in weight percent provided to the lubricating oil composition by the one or more ZDDP compounds divided by the amount of the one or more viscosity modifiers (VM) in weight percent based on a total weight of the lubricating oil composition is a P/VM quotient of more than about 0.0115, into a base oil to form the engine oil,

• the viscosity modifier is a linear polyolefin consisting of ethylene and propylene and having a shear stability index (SSI) of from about 3% to less than 30%, as measured using test method ASTM-D6278, and the engine oil composition provides a result in an Average Engine Varnish test (ASTM D8256) of 9.40 or higher, and
• wherein the one or more ZDDP compounds comprise a ZDDP compound derived from 100% secondary alcohols which are a mixture of methyl isobutyl carbinol and isopropyl alcohol and the amount of phosphorus from the one or more ZDDP compounds is about 787 ppmw to 1200 ppmw.