I use & highly recommend the use of synthetic oils in everything.
It lasts longer, protects better, and has a wider operating range with much superior thermal breakdown resistance. Plus it flows considerably better which equates to less power lost to parasitic drag.
Mobil 1 ATF plus FM in the MTX-75 "cocktail"
Mobil 1 ATF in the P/S
Valvoline Synpower in the brakes (Castrol Lima and HD Ford Blue are great Dot 4's as well - Remember any previously opened can of brake fluid is considered BAD! Moisture is it's mortal enemy! Once opened - use it all or just recycle the unused left-overs!)
Type F ATF is Mercon that has very thick friction modifiers added to it to prevent frothing & to help the clutch packs bite. (in an automatic) It greatly raises your parasitic drag.
Chrysler's ATF+3 & now +4 is Mercon with "newer" blends of friction modifiers that works more efficiently.
Mercon 5 is the only "semisynth" ATF spec. However heavy emphasis on semi. Maybe 15% synthetic base. It is also not compatatible with any other ATF.
P/S fluid would be considered a very light hydraulic oil. Low tolerance to high pressure, will burn up fairly easy, and has very little resistance to high heat thermal breakdown. Hence why it is not used is most cars anymore.
ATF provides much greater protection and a range of operations it is an ideal hydraulic oil to use. Most manufacturers have been using ATF in the P/S system for many years. (decades)
P/S steering fluid may have worked adequately on the old fashioned, low pressure, gear box pumps; but technology, component size and design & performance have come a long way in 30 years.
