Method of reducing the energy consumption of a hydraulic system, comprising applying a hydraulic fluid in a plastic injection molding process, characterized in that the hydraulic fluid composition comprises (i) a polyalkyl(meth)acrylate viscosity index improver consisting of monomer units of a) 10 to 25 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 6 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, and b) 75 to 90 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 7 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, wherein the weight average molecular weight (M w ) of the polyalkyl(meth)acrylate viscosity index improver (i) is 40,000 to 70,000 g/mol, and (ii) a base oil selected from API group I, II, III or IV base oils or mixture thereof, wherein the formulated hydraulic fluid has a fresh oil viscosity index of at least 160, a viscosity at 40°C of 15 mm 2 /s to 51 mm 2 /s, a density at 15°C of 800 kg/m 3 to 860 kg/m 3 . (i) a polyalkyl(meth)acrylate viscosity index improver consisting of monomer units of a) 10 to 25 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 6 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, and b) 75 to 90 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 7 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, wherein the weight average molecular weight (M w ) of the polyalkyl(meth)acrylate viscosity index improver (i) is 40,000 to 70,000 g/mol, and a) 10 to 25 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 6 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, and wherein R is equal to H or CH 3 , R 1 represents a linear or branched alkyl group with 1 to 6 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, and b) 75 to 90 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 7 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, wherein the weight average molecular weight (M w ) of the polyalkyl(meth)acrylate viscosity index improver (i) is 40,000 to 70,000 g/mol, and wherein R is equal to H or CH 3 , R 4 represents a linear or branched alkyl group with 7 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, wherein the weight average molecular weight (M w ) of the polyalkyl(meth)acrylate viscosity index improver (i) is 40,000 to 70,000 g/mol, and (ii) a base oil selected from API group I, II, III or IV base oils or mixture thereof, wherein the formulated hydraulic fluid has a fresh oil viscosity index of at least 160, a viscosity at 40°C of 15 mm 2 /s to 51 mm 2 /s, a density at 15°C of 800 kg/m 3 to 860 kg/m 3 . <EOS>