Oil for a Norton High Swing Grinder

1960's Norton High Swing Grinder, 48" OD capability What is the correct oil to use in the oil tank. This is where I would normally put hydraulic oil, say AW46. On top of the tank there is a tag and it reads" Use highly refined turbine oil " Could not really find this on the web.
A thought, this machine came out of a plant that rebuilds turbines so maybe that is why the callout?3


specs.

(1) Used 48" NORTON "High Swing" Universal Cylindrical Grinder; Chucking Type;


Specifications:


Swing Over Bed............................................50" (max)
Workhead Travel Left to Right....................18" nominal
Workhead Speed Range.............................10-200 RPM
Workhead Swivel Range..............................0° - 45°
Grinding Wheel Head Travel.......................16" nominal (in/out)
Grinding Wheel Diameter.............................24" (max)
Grinding Wheel Width................................... (max)
Grinding Wheel Speed Range................... 750 to 1200 RPM
Grinding Wheel Drive................................... Multiple V-Belt
Grinding Wheel Drive Motor.........................15 HP @ 1750 RPM
Electrical Characteristics..............................460 VAC / 3
Phase / 60 Cycle


Equipped With:
Complete Electrical Controls
16" T-Slotted Faceplate
Complete Telescopic Way Covers
Complete Hydraulic System
Complete Coolant System
2 Axis Profile Type Hydraulic Wheel Dresser
2 Axis Digital Read-Out
2 HP Vari-Speed Headstock Drive


Overall Dimensions......................................7'6" L-R x 8'6"
F-B x 84" High
Weight.........................................................12,000
lbs. (Estimated)

tanks