If the hydraulic system is required to operate in freezing temperatures in winter and tropical conditions in summer, then it will likely need multigrade oil to maintain viscosity within permissible limits across a wide operating temperature range. Typical Minimum Viscosity Values for Hydraulic Components Typical minimum permissible and optimum viscosity values for different types of hydraulic components are shown below. Permissible and optimum viscosity range for the system’s components Maximum expected operating temperature, which is influenced by maximum ambient temperature

Starting viscosity at minimum ambient temperature To choose the right fluid viscosity grade for your particular system, you will need to consider: How to Choose the Right Hydraulic Oil Viscosity or Grade If you choose a viscosity grade incorrectly, your hydraulic components will degrade faster than they should. It doesn’t matter how good the other properties of the oil are if the viscosity grade is not matched to the operating temperature range of the hydraulic system where it will be used. Picking the right viscosity grade (sometimes referred to simply as the 'hydraulic fluid grade') is the single most important factor when selecting a hydraulic oil or fluid. While it is not possible to make one definitive recommendation that covers all types of hydraulic equipment in all applications, there are a few key questions to ask yourself when selecting a hydraulic fluid. Which oil or fluid you choose depends on your equipment and how you plan to use it. Most hydraulic systems can operate using many different fluids, including multigrade engine oil, automatic transmission fluid and more conventional antiwear (AW) hydraulic oil.

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