An improved additive package including at least a polymeric amine antioxidants and a borated extreme pressure/antiwear agent for a polyol ester lubricant suitable for use in high temperature applications is provided. The lubricant fluid includes a base stock that is the reaction product of a polyol and monocarboxylic acid mixture including a major proportion of 3,5,5-trimethylhexanoic acid (iso-C9 acid). The additive package may be added in up to about 20 percent by weight of the lubricant to provide a viscosity of the lubricant at 40° C. of at least about 140 cSt and at 100° C. of no less than about 15.0 cSt. Greases are formed by adding a thickener to a high viscosity lubricating fluid.