A reservoir for power steering fluid includes an upright housing that forms an upper interior space for storage of a reserve fluid supply, and a lower interior space containing a fluid filter.* Fluid connectors are provided** for causing fluid to flow in a circumferential swirling pattern as it moves through the filter, such that the flowing fluid has a relatively long residence time in the lower portion of the reservoir for achievement of an effective cooling action. The fluid filter is connected in a return line from the power steering unit to the associated pump, so that filtered liquid is supplied to the pump. The fluid filter is preferably a flat disk-like filter unit located in a horizontal plane between the inlet fluid connector and the outlet fluid connector. *The upper interior space and lower interior space containing a fluid filter are separated by a frusto conical partition. Residence of the fluid above the frusto conical partition allows air entrained in the fluid to escape. **below the frusto conical partition.