Changing hydraulic fluid in late 1970's Case Drott 40 BEC excavator. Old fluid appears to be red - possibly ATF? Retracted as many cylinders to evacuate as much fluid as possible. Manual recommends Drott DHF fluid or as alternate SAE 20-20W for my temp range (50 degrees F to 210 degrees F - system temp). I do not plan on using this machine during the winter. Guy at NAPA recommended using ISO 46 (20W). Would this be a good subsitute? Any thoughts or recommendations would be appreciated.
As I recall, all those old machines used gear pumps so you didn't need any fancy high dollar oil for them. We always used AW46 hydraulic oil in them.
The old Drotts should be gear pumps. Those hydraulic systems don't really care about the oil, just as long as it's clean. We have standardized on aw32 (10w) for the hydraulic systems on our farm machinery. I don't see a problem with aw42, just keep in mind it will make your excavator rather sluggish in colder weather. ATF and hydraulic oil will have similar lubrication properties, so I would not worry too much about flushing the system when you change oils.