ATF vs CHF11s power steering

[2000Trooper]

Does anyone have factual information on if power steering fluid can be flushed out from ATF to CHF11s; if seal incompatibility an actual issue? It's too risky for me to even consider this given that my vehicle is only a couple of years old and I don't want to pay for parts that need to be replaced after a bad science experiment, especially given that the car isn't fully paid off yet. But I do enjoy asking these kinds of questions, researching them and learning.

There doesn't seem to be a whole lot of info on CHF online. I've only found that people praise it for it's properties, that only aviation grade hydraulic fluid is better than it, and that it's mineral based vs the petroleum derived stocks of ATF. CHF seems to be a clear winner in many aspects, yet I havn't seen anyone take the risk to switch. IF one were to do it, what issues could they experience since the two fluids are so different?

 

[clinebarger]

Whats wrong with using ATF?

 

[BMWTurboDzl]

CHF11s is hydraulic fluid and typically when this fluid is spec'd the seals used in the power steering system are only compatible with hydraulic fluid whereas ATF could cause them to swell and weaken. CHF11s has superior cold temp performance vs ATF.

My understanding years ago was that you could convert ATF to CHF11s but not CHF11s to ATF. Some manufacturers (ex, BMW) used the same steering system and either ATF or CHF11s and I wish I knew why.

 

[Falcon_LS]

I switched all my vehicles to CHF-11S across the board, and in the process, went through 2 liters of Pentosin CHF-11S in each vehicle until the fluid was pale green with zero traces of red.

Given its viscosity, the steering requires a bit more "muscle" when parking. The Ford power steering units in particular are as quiet as a church mouse.

As the fluid begins to darken, usually around the 3 year/35,000 mile mark, I change the fluid out. Perhaps a waste, but whatever helps you sleep at night.

Zero issues with pump noise, leaks, rack and pinion and recirculating ball units.

 

[tig1]

I've used M1 ATF for the better part of 30 years and have never had a PS pump fail or leak in a Ford.

 

[nthach]

A long time ago, Beck-Arnley was recommending CHF11s as an ATF substitute. In this application, ATF and CHF are both hydraulic fluids, which CHF being closer to a pure hydraulic fluid than ATF which is heavier and has more additives for lubrication and power transmission.

The viscosites are for sure different. BMW was saying ATF and CHF can be used interchangeably in some models. Others, like VW initially recommended ATF but changed over to CHF11s or CHF202.