Hello
What was the usage for power steering pump cooler? Depends on rear end ratio? My Hemicuda with 3.54 rear had it? 4 speed manual car. 71 Cuda 383 4 speed with 3.91? Thank you. Both were manual steering converted to power

yes, both of those would have a cooler with power steering - the coolers are different between Saginaw & Federal pumps

383 = Saginaw power steering pump
HEMI = Federal power steering pump

Higher gear ratio = higher rpm = higher fluid temp.
If that was your interest?

judging by the size of the coolers that I've seen, did they really do any reduction in temps? That is such a small cooler I honestly wonder if it did any temp reduction.

Never seen any tests or write ups about it.
I've never even tested my own PS fluid for temps.
Best guess would be if car is driven alot in heavy traffic, with lots of turning/idling (i.e. taxi), that may "stress" the fluid.
Those pumps are always turning & fluid is always being pressurized to an extent.
For most cars it's just a bling thing for sure.

I think it is used only on cars with short rear rear axle ratio, when engine is turning faster. My 6 pack 440 Challenger with a 3.23 doesnt have it. If Chrysler spent some money to install on a car, it was probably needed.

at what gear would the cooler become necessary ?

I read 3.54...would some expert say something on this matter....

I've read it was part of the axle package group. Guessing anything 3.54 and over ratio got it.

Owned a few 340 e-bodies with coolers. But they were 4-speeds with either 3:55 or 3:91, not 3:23. Both had the federal pumps

what about saginaw pumps ?

I have seen many Hemi with 354 dana with out a cooler ?