Killing The Myth: ATF vs PS Fluid

Insidious Surmiser

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In light of JJ's statement (and lack of input) on the usage of ATF and PS Fluid in the power steering system "I wish that myth would die" I intend on killing the myth myself (if at all possible) since he will not.

I've done about as much reading as I can. Couldn't really find much scientific information, just word of mouth. From what I can tell people have been interchanging the two fluids in their power steering systems in all makes and models in blatant disregard of factory specifications.

All I've managed to gather is that both are hydraulic fluids and that the additive packages are a bit different. Most people say that ATF will cause less wear, and should prolong the life of the pump in use.

I'll continue to read into this topic, and welcome any input anyone may have. I'll also update the main post with any factual information that may come to light

Scientific info:

as stated in MSDS,
major components of ATF: Solvent Refined, Hydrotreated Heavy Paraffinic Distillate
major components of PS fluid: Distillates (Petrolium), Solvent-Refined Heavy Paraffinic; Baseoil
 
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Insidious Surmiser

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Apparently the "old timers" that worked on cars when I was ~4 yrs old say that NAPA auto parts would sell fluid labeled as such "Automatic Transmission And Power Steering Fluid"
 

CyFi6

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They are both hydraulic fluids, so running either one shouldn't be a big deal, in fact you could probably get away with running many different kinds of oils. One issue is that there may be certain requirements for different materials used in the system, such as rubber hoses or seals. Honestly though, Toyota specifies ATF, so why would you use anything else? If I remember correctly the "myth" you are referring to is the fact that power steering fluid used in a system that calls for ATF will completely destroy and wreak havoc on the system. I don't see how this is possible unless you mixed two types of fluids that really did not get along with one another.

There is going to be speculation because nobody wants to or cares enough to investigate all the different requirements of all the different materials used in the specific system. Toyota did this already and recommends ATF, so that is what I use.
 

Insidious Surmiser

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yeah I've read cases where people have gotten away with using motor oil :-\ I'd simply rather stick with factory recommendation, and stay safe rather than sorry... besides, isn't ATF way cheaper than PS fluid?
 

Insidious Surmiser

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the only real issue I can see here is that oil does cause rubber to expand, so since oil is present in PS fluid but not ATF, I could see leaks developing as a result... as for the behavior of these two liquids under pressure, I haven't the least idea....

The only thing I can really logically assume is that ATF was safe for use as PS fluid... but I cannot be 100% certain if PS fluid is safe for use in a system designed for ATF
 

jdmfreak

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A few years back my roommate put a bottle of power steering fluid (with no label) with the brake fluid on the shelf

I grabbed it and filled my brake master cylinder with psf..... No good..... As I used My brakes they got tighter and tighter and within 5 miles were about completely locked up...

Had my truck towed to a tire place and they informed me that "somebody" had put power steering fluid in my master cylinder and that all rubber parts in the system were toast and would need to be replaced...

Now I took it home thoroughly flushed the system, replaced my master cylinder and everything was fine... But if psf is different from atf due to oil in the psf couldn't it essentially ruin the steering system like it did my brakes?

the only real issue I can see here is that oil does cause rubber to expand, so since oil is present in PS fluid but not ATF,
 
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CyFi6

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What exactly do you mean by ATF does not have oil? ATF is petroleum based. Also, the seals in a brake system are specifically engineered to be used with brake fluid, using anything besides a DOT approved brake fluid is a bad idea. If my system was ever contaminated with a petroleum fluid I wouldn't chance it...anything rubber in the system would be replaced including all the calipers.
 
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jdmfreak

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So the power steering system is designed for a petroleum product then the only thing that would make a difference between the two would be viscosity Right?

Or would that not be a concern?
 

CyFi6

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The additives and viscosity will vary from ATF to power steering and also from one brand to the next, but destruction of a system (ours) from using one vs the other is unlikely, the are both designed for use as hydraulic fluid. Using ATF or engine oil in your brakes is certainly destructive.

On the other hand, my MR2 for example had an electro-hydraulic power steering system utilizing an electric pump. The system called for a very specific fluid from Toyota (extremely expensive) and people reported several problems when using regular power steering fluid or ATF, but this is likely due to the pump itself. The EHPS fluid seemed to be a much lower viscosity than regular PS fluid.
 

3p141592654

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I have used ATF (Dexron 3) for many years in my PS system, along with a magnefine inline filter. I suspect that any oil meeting MIL-H-5606 would be an okay substitute.

Hondas are definitely not okay with ATF or regular PS fluid. They will foam like crazy and overflow the reservoir.

My wife's Volvo requires Pentosin 11s. "Extremely high VI of 320, thin CST, and supposedly very selective synthetic basestocks and additives make it special". Seems quite a few german cars also spec this. Far as I can tell, it works better at lower temps, but regular ATF would likely be fine in moderate climates.

As an aside, PS temperatures scale with engine rpm, not load. If you do long high rpm drives (track or mountain driving) temps will be an issue.
 
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Insidious Surmiser

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A few years back my roommate put a bottle of power steering fluid (with no label) with the brake fluid on the shelf

I grabbed it and filled my brake master cylinder with psf..... No good..... As I used My brakes they got tighter and tighter and within 5 miles were about completely locked up...

Had my truck towed to a tire place and they informed me that "somebody" had put power steering fluid in my master cylinder and that all rubber parts in the system were toast and would need to be replaced...

Now I took it home thoroughly flushed the system, replaced my master cylinder and everything was fine... But if psf is different from atf due to oil in the psf couldn't it essentially ruin the steering system like it did my brakes?
that's exactly what I was thinking in my previous statement "the only real issue I can see here is that oil does cause rubber to expand" in causing rubber to expand, oil also causes rubber to deteriorate, and weaken significantly

I understand ATF is a petrolium product, but lacks the base oil
 
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Daugherty_3

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I've was taught at school that if calls atf it can use either atf or ps fluid but if it calls for ps fliud only use ps fluid in it
 

IndigoMKII

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Which the redline comparisons, it seems the viscosity of the ATF fluid is more than the PS fluid. Could it be the toyota PS pump calls for ATF fluid due to the clearance between the gears being greater? Someone should disassemble one completely. This is going off the viscosity index.
 

ttsupra2503

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I've was taught at school that if calls atf it can use either atf or ps fluid but if it calls for ps fliud only use ps fluid in it
I was told the same thing. Keeping in mind that I would probably be flushing the system and using only one oil in the system once I got to a place where I was able to fix the issue/leak that made me mix oils in the first place.
 

Poodles

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Care to elaborate? I thought that this was the whole reason we have this "myth"....
But I have a suspicion you know more than you are sharing :p
Simple, some petroleum based products are used as beauty products and others will downright kill you. Being petroleum based doesn't mean much.

Redline may be an exeption, but from what I've seen in other places, the base stocks are usually different in the two fluids, and that's just for starters.
 

te72

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Interesting thread guys. I've never had a Supra that didn't have a leaky steering system, but I suspect that's due to a lack of maintenance by my part (or any other previous owner), so I never gave it much thought.

Might be worth noting, I've used PS fluid in my system, and likely on my other Supras as well. Can anyone say that they've only used one fluid or the other, and their results in regards to leaks?
 

Insidious Surmiser

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I know one of mine only had ATF in it, and it leaked like hell... (fluid probably saw almost twice the use it should have) the one I have now has PS fluid in it... it does not leak, however, the PS doesn't work very well :-/ work in progress....
 

IndigoMKII

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I've used new hoses since I rebuilt the engine and used PS fluid, the writing on the PS cap is worn off. Mine has leaked from day one, even with moving the hose and reclamping.
 

jdmfreak

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Interesting thread that contains some good observations. Congrats to the OP for making the effort. That said my comment applies only to older vehicles.
Duck!!! Incoming monkey wrench!!!

Lol so what is it about newer vehicles that makes it matter? Tighter clearances?

Oh and my buddy drove my supra the other day... (has atf) he was very impressed and kept commenting with how my power steering worked soo well (he uses psf) that being said these are 23+ year old pumps...
 

TurboJoe

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So which fluid is best suited for our cars? I read Dexron III is bad, VI isn't viscous enough, and so on. What is the official, current day fluid for an auto mk3?

Sorry for the noob question, I just want to make sure..

Thanks!

Joe
 

Nick M

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I'm wondering why some people have gotten noise with PS fluid?
And this should answer the question about Toyota telling you to put Dexron in the PS system.

ATF fluid. This thread is about power steering.... not sure how "auto" is playing into your inquiry.
Because ATF is AUTOmatic transmission fluid.

So, what is the myth?
 

Insidious Surmiser

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This thread was concluded some time ago...

The myth was that PS fluid and ATF are both fine to use for the same purpose. While both may work, one is better.
 

jdmfreak

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So which fluid is best suited for our cars? I read Dexron III is bad, VI isn't viscous enough, and so on. What is the official, current day fluid for an auto mk3?

Sorry for the noob question, I just want to make sure..

Thanks!

Joe
Nick this is the comment that was referred to "for an auto mk3"
 

Insidious Surmiser

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Who claimed that and where? And auto is because of ATF being automatic trans fluid. Get it yet?
Lots of people have made that claim. Lost of places. I understood you the first time, still don't get it. What do transmissions have to do with the power-steering system?