Foaming hydaulic system

I changed my hydraulic oil last week. I moved the return line to the waist oil tank and ran one item at a time using the 24 volt pump till the oil ran clean from each item. Than i fired up the power pack and ran it till the fluid ran clean using the wing motor.

I never let the fluid get below a quarter of a tank except when i used the drain valve to remove the old oil from the tank.

After the change I went back out to sea and ran the wing motor for 30 minutes, i have ran the bow thruster in each direction for a few minutes, ran the high output bildge pump for 3 minutes (did not want to over heat with no water flow), ran the winch back and forth a few times, and ran the windless in both directions for a few minutes.

I'm still getting some foaming in the tank. I changed the oil because the last test sample came back that i had some water contamination and the viscosity was low. I will send in a new sample next time i get to port to be tested. I don't think there is a leak as the fluid level has not changed and there is no oil film in the bildges.

Anyone have any ideas?

You may want to check the specs on your replacement oil to be sure it has anti-foam additive. If it doesn't, maybe it's "spindle oil", if it has the proper R&O additive, then the anti-foam additive can be added.
Foaming would normally be caused by a suction leak.

You got about as close as anyone could get. The auto past store that we ordered from gave us half hydraulic oil and half spindle oil. I will say it's our fault not checking all the labels as close as we should of. I was looking at the labels and they are close if you don't read each one.