Patent ID: 8012919

Claim:
A method of operating a diesel engine provided with an exhaust gas recirculation system comprising lubricating said engine with a lubricating oil composition comprising: a lubricating oil composition comprising: (i) a polymeric dispersant booster comprising monomer units of: a) 0 to 40 wt. % of one or more ethylenically unsaturated ester compounds of formula (I) wherein R is equal to H or CH 3 , R 1 represents a linear or branched alkyl group with 1 to 5 carbon atoms, R 2 and R 3 independently represent H or a group of the formula —COOR′, wherein R′ is H or an alkyl group with 1 to 5 carbon atoms, b) 10 to 98 wt. % of one or more ethylenically unsaturated ester compounds of formula (II) wherein R is equal to H or CH 3 , R 4 represents a linear or branched alkyl group with 6 to 15 carbon atoms, R 5 and R 6 independently represent H or a group of the formula —COOR″, wherein R″ is H or an alkyl group with 6 to 15 carbon atoms, c) 0 to 30 wt. % of one or more ethylenically unsaturated ester compounds of formula (III) wherein R is equal to H or CH 3 , R 7 represents a linear or branched alkyl group with 16 to 30 carbon atoms, R 8 and R 9 independently represent H or a group of the formula —COOR′″, wherein R′″ is H or an alkyl group with 16 to 30 carbon atoms, d) 0 to 30 wt. % of vinyl monomers, e) 7 to 25 wt. % of at least two N-dispersant monomers comprising: i) N-vinylpyrrolidinone, in amounts of up to 5 wt. %; and ii) at least one N-dispersant monomer one selected from the group consisting of dimethylaminopropylacrylamide, dimethylaminoethylacrylamide and tert-butyl aminoethylmethacrylate. wherein a)-e) add up to 100 wt.-%; and (ii) an oil of lubricating viscosity.