| abstract |
A method for improving deposit control and cleanliness performance in an engine lubricated with a lubricating oil by using as the lubricating oil a formulated oil. The formulated oil comprises a lubricating oil base stock as a major component, and a mixture of (i) at least one dispersant, and (ii) at least one viscosity modifier, as minor components. The at least one dispersant and the at least one viscosity modifier are present in an amount sufficient to have a critical dispersant thickening ratio of greater than 0.33. The critical dispersant thickening ratio is determined in accordance with the formula: n n n n n n n n Σ n n n [ n n G n n n n ] n n n * n n n dV n n n / n n n n d n n n [ n n G n n n n ] n n n n n n n Σ n n n [ n n B n m n n ] n n n * n n n dV n n n / n n n n d n n n [ n n B n m n n ] n n n n n n n n wherein [G n ] is the weight percent of each of n dispersants in the formulated oil, [B m ] is the weight percent of each of m viscosity modifiers in the formulated oil, dV/d[G n ] is the kinematic viscosity (Kv 100 ) increase of the lubricating oil per the weight percent of each of n dispersants in the formulated oil, and dV/d[B m ] is the kinematic viscosity (Kv 100 ) increase of the lubricating oil per the weight percent of each of m viscosity modifiers in the formulated oil. |