Be Ge pump

Use 30wt. motor oil. You should get enough responses to this. The motor oil costs a little more but the better quality is well worth it.
Craig

In my situation, I use implements with both newer tractors that use hydraulic oil and older Cats with Be-Ge pumps,  I put hydraulic oil in the Be-Ge pumps instead of SAE 30 to avoid cross contamination, and the Be-Ge pumps work fine with hydraulic oil. 

Thank you for all the responses. This system had hydraulic oil in it. I’ve drained the reservoir but the blade cylinders and hoses still have the hydraulic oil in them . Hmmm, decisions!  I know that I shouldn’t mix the different oils, so I’ll need to drain out the entire system. The hydraulic oil has been in there since 1960 when the Be Ge pump was installed by Berglund Tractor. The blade action is slow so the motor oil should speed up the response.
As a side note, the vibration damper had separated so I sent it to the Damper Doctors in Redding Cal. for repair. They did a great job. Which led to a radiator recored at Pankeys in Hayward and a new front pulley from Florin Tractor in Sacramento.

The Bee Gee pumps were originally designed to use 30W oil. That being said I have cheated and use the same Trans-Hydro fluid that I use in the John Deere's as it is more convenient. Never had any problems. My D4 has a Bee Gee pump. Other than that I would use 30W as originally specified.

I’ve been getting by just fine using 15W-40, as that’s what I keep on hand in bulk. I’ve used Hy-Tran and Chevron tractor hydraulic fluid as well.

Not just any hydraulic oil. Try and match the original oil viscosity.
An ISO 68 Hydraulic oil would be a pretty close match.
 [attachment=64282]Viscosity Chart.jpg[/attachment]