I would not use it to replace the average hyd oil. Some old eastern Europe tractors might be set up for such use.
In the old days you could filter the oil well and use it 1 to 10 or so in the fuel. Makes it smoke a little more. The new high-tolerance fuel delivery systems I'd be nervious messing up the spendy parts of the fuel pump and rail.
--->Paul
I'd be using it in old mechanical injected engines, not the new picky ones.