what oil to use in hydraulic steering system?
 

Imco external hydraulic steering system for 3 drives

regular power steering oil?
Transmission oil? what type?
Anything else?

Thanks again!

power steering fluid.

i used ATF on the last couple Zeiger systems (per Zieger) what are the pros and cons of ATF over power steering fluid?

Redline full synthetic power steering fluid or other synthetic if you are doing a complete flush, made a big difference on my duramax steering also.(as in quieter and better feel)

I always used the gm atf. Easier to see if you are getting water in it. Also use it in trim pumps.

"usually" the ATF has a higher viscosity then PS fluid....but depending on who makes it or if its synthetic that may not hold true...
ATF also has detergents in it to help keep "junk" buildup n the trans....does it help for the PS system...maybe on the pump seals and maybe for the rack-n-pinion system but for a HYD steering system i'm not sure if there would be any benefit one way or the other.
I know on my wife's jeep liberty, when it gets in to the single digits in the winter time her steering system whines so badly you think a cat is being murdered under the hood!! I switched out the PS fluid to ATF and it all went away! After reading online why, it turns out that jeeps use a plastic reservoir on a metal body...when it gets cold the metal shrinks and lets air into the system and cavitates the pump causing whine...the ATF has friction modifiers to help keep it from bubbling and that's what keeps it from whining!

I have used both PS fluid and ATF, never noticed a difference between them.

That is correct Zeigler recommends ATF

One thing I have notice - Volvo Penta steering actuators can have there own problems with fluid leaks on there own - but what I have notice thru out - is the apps that have used ATF instead of power steering fluid leaked more often. at least a 2 or 3 to 1 difference in apps. Just throwing that out there.

I am using 10W fork oil in my Zieger system.

I didn't have power steering fluid on the shelf.

No issues in 7 years.

Ken