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A lubricating oil composition comprising a major amount of an oil of lubricating viscosity and an additive system comprising (A) from about 0.1 to about 5% by weight of a detergent composition comprising at least two metal overbased compositions wherein said detergent composition consists essentiall

A lubricating oil composition comprising a major amount of an oil of lubricating viscosity and an additive system comprising (A) from about 0.1 to about 5% by weight of a detergent composition comprising at least two metal overbased compositions wherein said detergent composition consists essentially of (A-1) at least one alkali metal overbased detergent and (A-2) at least one calcium overbased detergent, wherein the ratio of total base number on a per 100 TBN and diluent-free basis contributed by the alkali metal detergent to the total base number contributed by the calcium detergent ranges from about 99.5-20 to about 0.5-80; (B) from about 1 to about 10% by weight of a succinimide dispersant; and (C) from about 0.1 to about 5 % by weight of a metal dihydrocarbyl dithiophosphate of the formula (I) wherein R1and R2are each, independently, hydrocarbyl groups containing from 3 to 13 carbon atoms, M is a metal and n is an integer equal to the valence of M. Also disclosed are methods for cleaning the combustion chamber of internal combustion engines, a method for reducing fuel consumption of internal combustion engines and a method for reducing NOxemissions of internal combustion engines.

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1. A lubricating oil composition comprising a major amount of an oil of lubricating viscosity and an additive system comprising (A) from about 0.1 about 5% by weight of a detergent composition comprising at least two metal overbased compositions wherein said detergent composition consists essentiall

1. A lubricating oil composition comprising a major amount of an oil of lubricating viscosity and an additive system comprising (A) from about 0.1 about 5% by weight of a detergent composition comprising at least two metal overbased compositions wherein said detergent composition consists essentially of(A-1) at least one alkali metal overbased sulfonate detergent having a metal ratio of at least about 10:1, and(A-2) at least one calcium overbased sulfonate detergent having a metal ratio of at least about 10:1, wherein the ratio of total base number on a per 100 TBN and diluent-free basis contributed by the alkali metal salfonate detergent to the total base number contributed by the calcium sulfonate detergent ranges from about (99.5-20) to about (0.5-80):(B) from about 1 to about 10% by weight of a succinimide dispersant; and(C) from about 0.1 to about 5% by weight of a metal dihydrocarbyl dithiophosphate of the formulawherein R 1and R2are each, independently, hydrocarbyl groups containing from 3 to 13 carbon atoms. M is a metal and n is an integer equal to the valence of M.2. The composition of claim 1 wherein the alkali metal comprises sodium.3. The composition of claim 1 wherein the hydrocarbyl substituted succinic acylating agent is reacted with an amine comprising a monoamine or a polyamine wherein the dispersant has a total base number of at least 40 on an oil-free basis.4. The composition of claim 1 wherein the dispersant is derived from a chlorine containing polyolefin wherein the polyolefin has {overscore (M)}nranging from about 300 to about 10,000 and has a total of tetra-and tri-substituted unsaturated end groups in an amount of up to about 90 mole percent based on the moles of said polyolefin reacted with chlorine wherein said chlorine is used on a molar basis up to about an amount equal to the moles of tetra-and tri-substituted end groups and reacting the mixture under time and temperature parameters selected to effect reaction of the polyolefin end groups and chlorine to produce a polyolefin reaction product having labile chlorine substituents.5. The composition of claim 4 wherein the dispersant is derived from an acylating agent prepared by forming a mixture of the labile chlorine containing polyolefin reacted with an α-ß-unsaturated compound, said compound comprising α-ß-unsaturated acids, anhydrides, derivatives or mixtures thereof and reacting the mixture under time and temperature parameters selected to effect reaction of the polyolefin with the α-ß-unsaturated compound to produce a polyolefin substituted reaction product having low chlorine content.6. The composition of claim 1 wherein one of the hydrocarbyl groups of (C) is an isopropyl group and the other hydrocarbyl group is 4-methyl-2-pentyl or a primary hydrocarbyl group.7. The composition of claim 1 wherein within (C) the metal is a Group II metal, aluminum, tin, iron, cobalt, lead, molybdenum, manganese, nickel or copper.8. A method of cleaning a combustion chamber of an internal combustion engine comprising the step of lubricating said engine with a lubricating oil composition of claim 1.9. A method of reducing the fuel consumption of an internal combustion engine comprising the step of lubricating said engine with a lubricating oil composition of claim 1.10. A method of reducing nitrogen oxides emissions of an internal combustion engine comprising the step of lubricating said engine with a lubricating oil composition of claim 1.