| abstract |
A base oil for hydraulic oil suitably used for hydraulic systems having filters of which micropore diameter is 50 μm or less is disclosed. The disclosure also provides a hydraulic oil composition using the above base oil, especially a hydraulic oil composition suitably used for such as tractors, transmissions, and common systems thereof having the hydraulic systems. The base oil has mineral oil, and the mineral oil is defined by kinematic viscosity at 100° C.: 1.5˜6 mm 2 /s, pour-point: −10° C. or less, viscosity index: 100 or more, % C P : 70 or more, % C A : 2 or less, and aniline point: 106° C. or more, and the mineral base oil is treated by catalytic dewaxing process and/or contains tertiary carbon atoms at a ratio of 7.4% or more to the total carbon atoms. |