| 摘要 |
The invention includes a tractor hydraulic fluid composition containing a major amount of a base oil mixture. The base oil mixture includes a first mineral oil having a kinematic viscosity at 100.degree.C of at least about 4.0 centistokes a nd a second mineral oil having a kinematic viscosity at 100.degree.C of at least abou t 7.0 centistokes. The tractor hydraulic fluid composition also contains a first polymethacrylate viscosity index improver and a second polymethacrylate viscosity index improver having a lower shear stability index than the first polymethacrylate viscosity index improver. The tractor hydraulic fluid composition has an unsheared kinematic viscosity at 100.degree.C of at least abo ut 9.1 centistokes, a sheared kinematic viscosity at 100.degree.C of at least about 7.1 centistokes, and an unsheared kinematic viscosity at -40.degree.C of not mor e than about 20,000 centipoise.
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