I'm learning more about hydraulics and diesel engines.
The R and O is anti-Rust and anti-Oxidation.
HOLY SH^%. Two bald eagles just flew by outside my window, about 20' from the house. I'm only about 300' from a creek that empties into the Puget Sound about 0.5 miles from here.
Back to the regularly scheduled programming...
There is a balancing point between the viscosity being thin/ thick enough to be effective...
"Although many manufactures of hydraulic fluid provide various grades of detergents and oxidation stability in the fluids they produce, the single factor that should weight the heaviest in determining the best choice of fluid to use is viscosity, otherwise known as the fluid's weight. Viscosity is also most often expressed as the fluids ISO number or grade.
Common ISO grades for use with hydraulic systems include 32, 46 and 68. Sometimes, 10, or 10 weight is mentioned as well. I would like to point out that for basic operation of any hydraulic system without concern to long-term effects of the systems life, 10W-40 automotive engine may be used, providing it does not contain degertant additives, and these additives used in engine oil can cause corrosion and cavitation. This occurs because the detergents can cause water that has condensed into the system to emulsify, preventing it from being seperated from the oil.
It is recommended however, that a proper hydraulic fluid be used, and chosen based on its ISO grade. These fluids do not contain harmful additives that can cause damage to components, and are designed to work within a specific temperature range. "
Higher viscosity hydraulic fluid tend to reduce the system's operating temperature by increasing the volumetric efficiency of the pump. If the viscosity is too high, however, will cause poor mechanical effieciency by increased friction during startup, and may lead to cavitation. Finding the right ISO grade that balances the benefits of volumetric effeciency against the drawbacks of mechanical efficiency is the key to a good long term oil choice. Ultimatly the manufacturer of the equipment knows this value and is always best to consult the manufacturer to try to obtain the answer.
Manufacturer knows best.