I bought hydraulic fluid at NAPA, showed them a picture of the 10W20 product I wanted, paid, but they brought out a 30W product and put it in the car.  I didn't pay attention that they didn't give me what I asked for.  Anyway, the pump works well but sometimes it takes a while longer than desired to prime.  Nobody uses SAE oil ratings for hydraulic fluid any more, and it's not clear what the best ISO grade to use is:

SAE 10 weight viscosity:  45mm**2/s at 40C, 7.0mm**2/s at 100C

SAE 20 weight:  61mm**2/s at 40C, 8.5mm**2/s at 100C

ISO 32 weight:  32mm**2/s at 40C, 5.5mm**2/s at 100C

ISO 46 weight:  46mm**2/s at 40C, 7.0mm**2/s at 100C

ISO 68 weight:  68mm**2/s at 40C, 9.5mm**2/s at 100C

None of the ISO ratings match the original specs.  I don't suppose those were too precise.  I'm inclined to go with ISO46AW.  But that seems to equate more closely to a SAE 10 weight.  Hopefully, the "AW" additives will help make up for any differences.  yes/no?

Why are they rating these at 40C??? that's 104F (and 212F).

Considering the 'relatively' light work your CA will likely see in Texas, I would use the ISO 32. If you intend to cultivate cotton in 95 degree heat for 12 hours at a time then use the ISO 46.

The ISO 32 works perfectly in my somewhat cooler climate here in northern Idaho, ISO 46 is somewhat sluggish.

At some point, AC added a check valve in the inlet, presumably to improve priming.  1952 doesn't seem to have a check valve/ball.  It's a minor problem, but sometimes it can take 10-15 seconds (or longer if its cold) before it starts to pump, usually on a fresh startup.  May be a combination of wear and oil viscosity.  With thicker oil, it was nearly impossible to get it to prime.

That's roughly what it has in it (821Xl compliant).  That's roughly 10W30 and it has trouble priming sometimes.

The tractor is in Indiana.  It will have a relatively easy life for the foreseeable future.  It may on occasion do some plowing/discing.  My brother is eyeing it for his garden.   It may be used for some brush hogging if I get the smaller one working, but mostly finish mowing.

Here’s a handy chart to help you find the equivalent ISO grade for a given SAE weight:

SAE	ISO/AW
10W	32
15W or 20W	46
20W	68
30W	100

This oil conversion chart is approximate.

Note: ISO grades overlap with SAE weights in some cases. For instance, ISO 46 can replace both SAE 15W and 20W oils depending on the temperature.

Yup, I saw that.

That's what I have in it now and it isn't quite behaving as I'd like.  Once it primes, it's fine.  I know that it has trouble priming with thicker oil.  I just don't want to run something that's too thin.