Use of a comb polymer for reducing the loss in viscosity of a lubricating composition for the crankcase of an internal combustion engine, wherein the internal combustion engine is fuelled with a fuel composition which comprises a fatty acid alkyl ester, wherein the comb polymer comprises, in the main chain, at least one repeat unit which is obtained from at least one polyolefin-based macromonomer, and at least one repeat unit which is obtained from at least one low molecular weight monomer selected from the group consisting of styrene monomers having 8 to 17 carbon atoms, alkyl(meth)acrylates having 1 to 10 carbon atoms in the alcohol group, vinyl esters having from 1 to 11 carbon atoms in the acyl group, vinyl ethers having 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumurates having 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having 1 to 10 carbon atoms in the alcohol group and mixtures thereof, wherein the molar degree of branching is in the range of 0.1 to 10 mol%; wherein the comb polymer comprises a total of at least 80% by weight, based on the total weight of repeat units of the comb polymer, of the at least one repeat unit which is obtained from the at least one polyolefin-based macromonomer and the at least one repeat unit which is obtained from the at least one low molecular weight monomer; wherein the comb polymer has a weight-average molecular weight in the range of 100,000 to 500,000 g/mol; wherein the molar degree of branching, f branch, is calculated by the formula: ƒ branch = ∑ a = 1 A n a ∑ a = 1 A n a + ∑ b = 1 B n b where 'A' is the number of types of repeat units which are derived from polyolefin-based macromonomers; where 'B' is the number of types of repeat units which are derived from low molecular weight monomers selected from the group consisting of styrene monomers having from 8 to 17 carbon atoms, alkyl(meth)acrylates having from 1 to 10 carbon atoms in the alcohol group, vinyl esters having from 1 to 11 carbon atoms in the acyl group, vinyl ethers having from 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumarates having from 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having from 1 to 10 carbon atoms in the alcohol group, and mixtures of these monomers; where n a number of repeat units which are derived from polyolefin-based macromonomers of the type a in the comb polymer molecule; where 'n b ' is the number of repeat units which are derived from low molecular weight monomers selected from the group consisting of styrene monomers having from 8 to 17 carbon atoms, alkyl(meth)acrylates having from 1 to 10 carbon atoms in the alcohol group, vinyl esters having from 1 to 11 carbon atoms in the acyl group, vinyl ethers having from 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumarates having from 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having from 1 to 10 carbon atoms in the alcohol group, and mixtures of these monomers, of type b in the comb polymer molecule. where 'A' is the number of types of repeat units which are derived from polyolefin-based macromonomers; where 'B' is the number of types of repeat units which are derived from low molecular weight monomers selected from the group consisting of styrene monomers having from 8 to 17 carbon atoms, alkyl(meth)acrylates having from 1 to 10 carbon atoms in the alcohol group, vinyl esters having from 1 to 11 carbon atoms in the acyl group, vinyl ethers having from 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumarates having from 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having from 1 to 10 carbon atoms in the alcohol group, and mixtures of these monomers; where n a number of repeat units which are derived from polyolefin-based macromonomers of the type a in the comb polymer molecule; where 'n b ' is the number of repeat units which are derived from low molecular weight monomers selected from the group consisting of styrene monomers having from 8 to 17 carbon atoms, alkyl(meth)acrylates having from 1 to 10 carbon atoms in the alcohol group, vinyl esters having from 1 to 11 carbon atoms in the acyl group, vinyl ethers having from 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumarates having from 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having from 1 to 10 carbon atoms in the alcohol group, and mixtures of these monomers, of type b in the comb polymer molecule.