A diesel fuel composition comprising a first additive (i) comprising a quaternary ammonium salt and a second additive (ii) comprising a Mannich reaction product; wherein the quaternary ammonium salt additive (i) is formed by the reaction of a compound of formula (A): R O O R1 10 (A) and a compound formed by the reaction of a hydrocarbyl-substituted acylating agent and an amine of formula (B1) or (B2): 15 N X R3 R2 NHR4 N X R3 R2 [O(CH2)m]nOH (B1) (B2) wherein R is an optionally substituted alkyl, alkenyl, aryl or alkylaryl group; R1 is a C1 to C22 alkyl, aryl or alkylaryl group; wherein R2 and R3 are the same or different alkyl, alkenyl or aryl groups having from 1 to 22 carbon atoms; X is a bond or alkylene group having from 1 to 20 20 carbon atoms; n is from 0 to 20; m is from 1 to 5; and R4 is hydrogen or a C1 to C22 alkyl group; and wherein the Mannich reaction product additive (ii) is the product of a Mannich reaction between: (d) an aldehyde; (e) an amine; and25 (f) a substituted phenol; wherein the phenol is substituted with at least one branched hydrocarbyl group having a molecular weight of between 200 and 3000.

This invention relates to a lubricating oil composition comprising or resulting from the admixing of: a) 50 to 99 mass % of one or more base oils; b) 0.1 to 15 mass % of one or more functionalized olefin copolymer having an Mn of from 10,000 to 35,000 g/mol; c) 0.1 to 20 mass % of one or more detergents wherein the detergent comprises at least one calcium detergent having a TBN of more than 100 mg KOH/g; at least one calcium detergent having a TBN of 100 mg KOH/g or less; and at least one magnesium detergent, where the difference in the TBN's for the Ca detergents is at least 100 mg KOH/g; d) 0.01 to 40 mass % of one or more dispersants wherein the dispersants comprise at least one borated dispersant and at least one non borated dispersant; e) 0.01 to 20 of mass % sulfurized fatty acid ester; f) 0.01 to 5 mass % of one or more amine or phenol based antioxidants; and g) 0.001 to 15 mass % of molybdenum containing compound, where the lubricating oil composition has: 1) a sulfated ash content of 0.9 mass % or less; 2) a Mack T-11 final soot %@15 cSt of 6.7% or more; 3) a total base number of 5 to 30 mg KOH/g; 4) HTCBT of copper level increase of 20 ppm or less; 5) T-13 IR peak EOT of 40 abs/cm or less; and 6) Cam wear outlet of 45 m or less.