Kent,
I was hoping someone would join this discussion, one whom had deeper knowledge of the subject. I've picked up what I know about oils by using them, and from our local tractor dealership partsman who went to a seminar once.
Polymers are what make multi-weight oils multi-weight, they are compounds related to plastic that make the oil thicken up when warmer. Complex chemestry involved here, I o know that one should never mix multi-weight oils of different viscosities, even of the same brand.
I would shy away from motor oil, even non detergent. But as I also said any oil is better than none. If I was to use 10w motor oil I would use a non detergent.
Hydralic oils have a much better film strenth, same for the ATF. I'm really not sure about the Power steering fluid.
We use universal transmission hydralic at work, seemingly no ill effects. It also make a good heat treat oil, since hydralic oil has a high flash point. Plus it doesn't have that red dye like ATF, when that mill head drips on table it won't look like it's bleeding.
I used to use motor oil in the spindle bearings of an old lathe I have, until I ran out one day, bearings would get tight if running it at higher speeds. I searched the shop over, only oil I could find was some hydralic oil, in it went, bearing never even acted like it was getting tight after that. I've kept hydralic oil in my oil can ever since, use it for everthing except in the crankcase of an engine.
