The present invention concerns a functional fluid comprising A) 1 to 99% by weight based on the total weight of the functional fluid of alkyl(meth)acrylate polymers obtainable by polymerizing a mixture of olefinically unsaturated monomers and B) 1 to 99% by weight based on the total weight of the functional fluid of an oxygen containing compound selected from to group of organophosphorus compounds, carboxylic acid esters and/or polyether polyols.