depends on the vis of oil higher less volitile also how hot oil gets and how long and airation of oil all will effect evap loss how much that would be is unkown since all the above peramiters maybe diferent on any given gear box. I think it is minimal and any low oil conditions should be caught at normal or routine oil level/testing/service intervals. bruce
Agree entirely with Bruce, potential for loss due to volatility in Hydraulic and turbine is virtually nil.(if blended sensibly) Engine oils also likely to be no different as part of the spec. is a test for volatility(Noak) Possible loss in some poorly designed turbulent systems due to oil mist through breather and should be obvious to see.