Originally Posted by Jim Shea

Here is a paper that I authored on the evolution of GM power steering fluid.

Originally Posted by Jim Shea

Here is a paper that I authored on the evolution of GM power steering fluid. When Saginaw Steering Gear was a division of General Motors and was steering responsible, they had a lot of clout (along with Oldsmobile Division) and kept things in good order with respect to fluids, specs, etc. Here is the paper:
Jim
GM POWER STEERING FLUID

Originally in the 1950’s, automatic transmission fluid (ATF) was specified for use in both General Motors automatic transmissions and also for their power steering systems. But as vehicles got heavier, engines bigger, and temperatures hotter, the requirements for the two different systems changed. The GM Research Labs had a Lubricants Section that began testing and modifying the ATF formulation to improve the performance of the GM Hydramatic, Dynaflow, and Powerglide transmissions. They did this without much regard to the fact that the power steering system was using the ATF fluid as well. Sort of the tail being wagged by the dog.

So around the same time, Saginaw Steering Gear Division and Texaco began testing and developing a fluid specifically for power steering. The fluid characteristics were specifically formulated to provide anti-corrosion and non-foaming qualities with excellent lubrication for year around use. There was also particular emphasis placed on wear testing performance with respect to the vanes, rotor, cam ring, and the driveshaft bushing in the big Saginaw “P” model power steering pump. By the way, the “P” model was the only power steering pump used in all C2/C3 Corvettes and all GM passenger cars and light trucks with power steering in the 1960s and 1970s.

That is why some of the early power steering reservoir caps had ATF specified as the proper fluid to use. All the later pump caps and the owner's manuals have said to use "Approved Fluid". The GM power steering fluid is approved for use in any vehicle with a Saginaw power steering pump.

To be honest, all of the Saginaw power steering pumps adapt fairly well to all kinds of fluids. The pumps are marketed and sold all over the world and are used by many vehicle manufacturers who specify their own power steering fluids. Chrysler in the past has used a very simple mineral based fluid. They eventually changed to GM power steering fluid. I am not sure if they still use GM fluid today or not. Ford uses a special Ford ATF fluid. VW uses a European brand of fluid called Pentosin. All of these fluids reportedly work well in their vehicles.

I have no idea who formulated the PS fluid that is sold at K-mart, Pep Boys, NAPA, etc. This isn’t to say that it is bad. However, the amber colored GM fluid is the only fluid that has been certified and tested in GM durability test vehicles for millions of miles. It also is the only fluid that have been durability tested in the Saginaw Steering Gear engineering labs for hundreds of thousands of hours. All of the rubber compounds that are used in the seals, hoses, etc in the production GM power steering system are tested in the materials laboratory for compatibility with the fluid.

The GM part number for a quart of power steering fluid is 89020661. The previous GM part number for power steering fluid was 1050017. Both fluids work equally well.

BTW, there is a recent push to use Dex 6 automatic transmission fluid as a “universal” fluid for power steering systems was well as automatic transmissions. Nexteer (formerly Saginaw Steering) engineers report that the Dex 6 fluid does NOT perform as well as genuine GM power steering fluid.

Originally Posted by aussiejohn

Jim, thank you for your detailed explanation of the whole GM power steering fluid development over the years. With your permission I would like to print out copies of this to show to my future customers. After reading this, there should be no argument as to the correct fluid to use in their integral power boxes.

Regards from Down Under.

aussiejohn