The National Fluid Power Association (USA) has defined the Temperature
Operating Window (TOW) for hydraulic fluids as the range of temperature
over which a fluid can operate and meet the OEM's viscosity requirements.
The majority of pump OEM's have set a minimum operating viscosity of 10 cSt
at operating temperature, and a maximum viscosity of 750 cP at cold
start-up temperature. The following calculator will allow you to
determine the TOW for any fluid viscosity grade and viscosity index.