Well, over the years, I've used a variaty of fluids in a power steering system. Most of the time I used actual power steering fluid out of bottles marked as such.
But, if I did not have access to any, I usually used type "F" transmission fluid. Dextron was either not invented yet, or fairly unknown back then.
When it started getting common, most of the transmission guys I knew, considered Dextron to be "thinner" than the older fluids.
Once, when faced with a 1500lb piece of equipment sitting on a lift gate that had leaked out all its fluid, I fixed the leak and filled it with motor oil. 10W40 if I remember right.
It worked fine, and I was going to get it replaced when I got back to the shop, but I forgot for about 3 months, during which time it worked fine.
Of course, that was very intermittent duty. Continuous use might foam or cause other problems.
I like Amsoil lubricants for most of my needs, so when I got my new Mahindra tractor, I wanted to switch it over. The motor oil was fairly simple, but the transmission was another matter.
Amsoil does not list a replacement for Mahindra.
And, I left something off, so let me add this in an edit.
The Mahindra manual lists the specs for the fluid, and in addition to their part numbers, they list GL-4 as being a replacement.
For folks who are not farm tractor knowledgeable, let me expand on what Diesel4me said.
My tractor, like most of them, uses the same fluid for the manual transmission, rear axle differential, wet brakes, hydraulic lift on the back, the hydraulic cylinders on a front end loader if mine had it, and the power steering.
Not the same type of fluid, the actual same fluid for all. In other words, you have a common sump that all those systems uses. The same fluid circulates through all those.
Which means, that fluid has to be power steering fluid, rear end lube, transmission fluid, hydraulic fluid and brake friction modifier.
So, the choice of what to use is fairly critical.
GL-4 is often spec'ed for rear ends and transmissions in regular trucks. Its a lot thinner than you would expect for that use, but they run Dextron in NP-205s with no problems, so I guess gear lube can be thin and still do its job.
Although I like a little thicker lube for sliding gears like a ring and pinion. And GL-4 is thicker than Dextron.
This is what I use:
https://www.amsoil.com/shop/by-prod...lic-transmission-oil-sae-5w-30/?code=ATHQT-EA
If you look at the specs, it says GL-4, and the list of companies whose requirements it meets is impressive.
So far, with over 500 hours on the machine, I have had no problems with the lift or the steering. I would expect any problems with the rear end or transmission to show up later unless the stuff was totally worthless for that use.
I have used the lift in 20 degree weather and 100 degree weather with the oil temp over 100 and no noticeable decrease in lift capacity which I would expect if the oil thinned out too much.
Would it work in a truck power steering? No idea.
FWIW, the steering on the tractor is full hydraulic using a ram, no rack and pinion or recirculating ball, so its not a good comparison.
But, if I were stranded somewhere needing power steering fluid and had some of this, I would not feel apprehensive about putting it in.
Or, you could just do like this friend of mine. I just did the final update on it. It veers off into some medical stuff, but the power steering info is there.
https://ck5.com/forums/threads/well-this-beats-me-last-update.333812/