Water levels in Hyd systems using eng oil?

Engine oil has is better to keep the moisture dissolved compared to hydraulic oil. I would agree with the statement that up to 2000 ppm (0,2%) is acceptable in engine oil.

(Also I think you will not manage to keep water level as low as you can with hydraulic oil).

But wont the water still cause problems at such high levels. I would have thought that the fluid film strength of the oil is still compromised wether it be engine oil or hydraulic oil.

I dont think those levels of water in engine oil used in hydraulic systems will cause any problems. If I am wrong, there is thousands of machines with potential problems around the world. I think most of ie. earth moving machines accept the use of engine oil in hydraulic systems.

I have not seen any facts about oil functionality (film strength, lubrication properties) in this scenario. I belive you need free water droplets in the oil to reach cavitation, microbacterial growth, corrosion and other "normal" problems.

I have tryed to remove moisture from this kind of oil, and was not able to reach bellow 0,1% with vakuum purification.

The main problem of using engine oils in hydraulic applicatins is the additive package , especially the calcium compound. When the hydraulic system is an open system, your filter will be blocked soon. If not I forsee no problem if the the watercontent is lower than the saturation point of the oil.You have to take into account that a measurement of the watercontent is influenced by these detergents.