Does anyone now if using engine oil in hydraulic systems ie Sandvik units would allow the system to maintain higher water levels before rejection. We have been told that up to 2000ppm is within limits. This i find very hard to believe but would love some hard evidance.

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.