Oil composition for lubricating an EGR equipped diesel engine and an EGR equipped diesel engine comprising same

1. 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.

2. The method of operating a diesel engine of claim 1 , wherein said polymeric N-dispersant booster is present in an amount of at least 1 wt. % based on the total weight of the oil composition.

3. The method of claim 1 , wherein monomer b) comprises C 10-16 methacrylate.

4. The method of claim 1 , wherein said N-dispersant monomer is at least one selected from the group consisting of dimethylaminopropylacrylamide, dimethylaminoethylacrylamide, and tert-butyl aminoethylmethacrylate.

5. The method of claim 1 , wherein said N-dispersant monomer is dimethylaminopropylacrylamide

6. The method of claim 1 , wherein said N-dispersant monomer comprise N-vinylpyrrolidinone, in amounts of up to 5 wt.%.

7. The method of claim 1 , wherein said polymeric dispersant booster has a number average molecular weight Mn of from 50,000-500,000.

8. The method of claim 1 wherein said polymeric dispersant booster has a shear stability of from 2-55 % as measure by the 30 cycle Kurt-Orbahn (Bosch diesel injector) test.

9. A diesel engine provided with an exhaust gas recirculation system comprising 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.