[fuzzcar]

What is the best power steering fluid to use with a brand new 670 steering box?

Everything else is new as well. This will be for daily driving.

 

[Navy Lifer]

Use GM fluid - don't try to go cheap or fancy

In your location, consider using GM cold-climate PS fluid

Lee Manufacturing will tell you the same thing.

 

[fuzzcar]

Should I use the cold climate fluid? In the winter it gets down to about 10 on occasion but in the summer we can see 100+

 

[sonuvah]

As quoted by Jim Shea in one of his many GM steering articles:

"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."
http://jimshea.corvettefaq.com/?cat=4

 

[Navy Lifer]

You should have no issues with the cold-climate fluid or the fluids John mentions. Being formulated for better cold-climate performance doesn't mean it's not going to work as well on 100-degree days.

Lee Manufacturing also sells their own fluid:

POWER STEERING FLUID

Lee power steering fluid and it's proprietary blend of additives is the oil of choice among many professional race teams. The increased lubrication quality of this non-synthetic fluid is just one of the reasons to use our oil.

Special anti foaming agents and high pressure co-molecules are blended to exact specifications for the best power steering oil period.

Bottled in a quart and gallon sizes, this power steering oil is tested tuff and has conquered the Baja 1000 time and time again, used in all arenas of racing, off road, monster truck, NASCAR, sprint car, modifies and high performance street vehicles, IT GETS THE JOB DONE.