The present invention is directed to oil-soluble lubricating oil viscosity index improver/dispersant additives comprising Mannich Base condensates of a grafted ethylene copolymer, an optionally alkyl-substituted N-hydroxyaryl compound, an aldehyde, and a monosecondary amine, whereby oil solutions, particularly oil concentrates, of said additives which are characterized by minimal viscosity change over an extended period of time. These additives comprise a copolymer of ethylene with one or more C.sub.3 to C.sub.28 alpha-olefins, preferably propylene, which have been grafted with acid moieties, e.g. maleic anhydride, preferably using a free radical initiator in a solvent such as a lubricating oil, which is then either (a) reacted with an N-hydroxyaryl amine and then condensed with an aldehyde and a monosecondary amine to form the Mannich Base viscosity index improver/dispersant material, or (b) reacted with a preformed Mannich Base condensate of an N-hydroxyaryl amine, aldehyde and the monosecondary amine. The invention also relates to process for preparing the preceding products and their use in oil compositions.