V8 guys - Power steering fluid or Transmission fluid for steering?

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I'm currently running power steering fluid, but will switch over to ATF shortly. From what I understand, it's the steering box that is specific to the fluid, not the pump, so as long as you have the stock steering box, you need to use the fluid that is intended for it, which is ATF.
 
Well.... I've been runing GM P/s fluid in my swap.
 
I have done 4 swaps to date with one of them now over 6 years old and a daily driver .That being said I use power steering fluid with a tranny cooler rated to 10000 lbs towing and not one problem as of yet.That is with using both stock pump and a gm saginaw.
 
I've been using power steering fluid in my swap. I think the GM pump must have a little more pressure then the toyota did since the steering is easier since the swap. Doesn't whine when its cold either!
 
GM FSM calls for power steering fluid in the pumps that come on the 5.3L Vortec. I'm pretty sure GM has recommended power steering fluid since the 60s or 70s for their applications. My thinking is that because the PS pump is spinning much faster then anything in the PS box, the appropriate fluid for the pump should be used.
I've read online that GM mechanics will tell you that the seals in the PS box aren't designed for ATF, so that should not be used as ATF will cause them to deteriorate. I'm yet to ask one personally though. Maybe the same goes for using PSF in the Toyota box, but it sounds like using PSF in Toyotas makes the pumps fail, not the box.
 
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That's precisely why I'm using ATF in my pump. PS pumps are typically far less expensive to repair or replace than gearboxes. I would rather replace a few pump seals or pumps than a steering box any day. Is there that big of a difference between PS and ATF fluid?
 
What I'm saying is that is seems like the PS box is not sensitive to PSF like the pump is.
PSF has an anti-foaming additive, and I would think ATF would have some additive the helps the torque converter and the shifting. Ford uses a different fluid then GM which causes the shifts to be harder. So it even varies from one ATF to another. They are both similar fluids as they are a form of hydraulic fluid.
 
Toyota pumos ( at least old ones ) use ATF .. and all T and P type pump use power steering or just hydraulic fluid ..
 
ATF has a rubber swelling agent in it to keep the internal seals in the trans soft and working. If the seals used in the PS system are not formulated from rubber with this in mind the ATF can swell the seals and cause a leak. That is the reason behind running a quart of ATF in an engine with leaking seals. The idea is to soften and swell the old seals in the hope that you don't have to re-seal the engine.
 
I'm switching from ATF to power steering fluid as we speak. PSF is a little better than ATF for this application. It holds more pressure wereas ATF in an automatic stays in the hundreds, the power steering system can get into the 1000psi range.
 
Wow, I'm wondering why no one's asked this before? It seems there's a lot of differing opinions.

Boots makes a good point with the pressure of the power steering fluid. I guess I'll be using PSF for my application.
 
Yes, boots makes a good point. However, they are both hydraulic fluids. Why don't we just say use what you want to use? Some use ATF, some use PSF. I may switch over to PSF in the future once I finally get the thing on the road.
 
I use ATF on my factory 80 series yota pump .. but as I contact PSC and ask about the right fluid to use in their pump .. I'm using PS fluid in my PSC pump ..
 
Other than the potential for heat, what difference would it make to the fluid what the system's operating pressure is?

I agree with the idea to run what you're comfortable with. In a hybrid system (pump uses one, box wants the other) I think that I'd start with PSF and watch for weepage. If that stared I'd add ATF, but that's just my approach. I don't think that it's superior to any other.
 
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