Patent ID: 7560420

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) 80 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) about 10 wt.% of at least one substituted styrene substituted with a substituent selected from the group consisting of halo-, amino-, alkoxy-, carboxy-, hydroxy-, sulfonyl- and C 1-12 hydrocarbyl, e) 4 to 7 wt.% of an N- dispersant monomer of at least one of N-vinylpyrrolidone and a dialkylaminoalkyl (meth)acrylate, wherein a)-e) add up to 100 wt.-%; and (ii) an oil of lubricating viscosity.