Patent ID: 7651985

Claim:
A method for improving the oxidation stability of an ashless hydraulic fluid or an ashless paper machine oil, comprising: a. selecting a base oil having: i. greater than 90 wt % saturates, ii. less than 10 wt % aromatics, iii. a base oil viscosity index greater than 120, iv. less than 0.03 wt % sulfur, v. a sequential number of carbon atoms, vi. greater than 35 wt % total molecules with cycloparaffinic functionality, and vii. a ratio of molecules with monocycloparaffinic functionality to molecules with multicycloparaffinic functionality greater than 2.1; and b. replacing a portion of an original base oil in the ashless hydraulic fluid or ashless paper machine oil with the selected base oil to produce an improved ashless lubricating oil; wherein the improved ashless lubricating oil has a result in the rotary pressure vessel oxidation test by ASTM D 2272-02 at 150 degrees C. that is at least 50 minutes greater than the result in the rotary pressure oxidation test of the ashless hydraulic fluid or ashless paper machine oil.