Base fluids

A hydraulic fluid comprising a base fluid and one or more functional additives, characterized in that the hydraulic fluid comprises, based on total hydraulic fluid, from 10% by weight to 95% by weight of a base fluid comprising an esterification product, having an acid number below 10 and a hydroxyl number below 15, obtained by esterification of:

• (a) a polymerized unsaturated C.sub.12 -C.sub.24 fatty acid selected from the group consisting of dimer acid, trimer acid, hydrogenated dimer acid, hydrogenated trimer acid, and mixtures thereof;
• and
• (b) a monohydric alkoxylated alcohol selected from the group consisting of:
• (1) straight or branched chain, saturated monohydric alcohols having from 1 to 24 carbon atoms, which are alkoxylated with from 6 to 12 moles of a C.sub.2 -C.sub.5 alkylene oxide, and
• (2) alkoxy poly(alkylene) glycols in which one of the two terminal hydroxyl groups is etherified with a C.sub.1 -C.sub.4 aliphatic monohydric alcohol and which is alkoxylated with from 6 to 12 moles of a C.sub.2 -C.sub.5 alkylene oxide, and optionally,
• (c) a straight or branched chain, saturated monohydric alcohol having from 1 to 24 carbon atoms,
• until the acid number of the ester is below 10 and the hydroxyl number is below 15.