For some reason recently, many people have been asking me about ATF Cooler Lines.
So this is just a simple and short PSA:

Any of you that have a Vehicle with the OEM/ Stock Automatic Transmission Cooler-Lines (especially older Vehicles/ Classics)...
A simple, easy, and inexpensive upgrade for your Automatic Transmission/ Vehicle, is to change to 3/8" or -6AN Cooler Lines.

Getting rid of any 5/16" or even tiny 1/4" Stock Cooler Lines, will alleviate restriction in the Cooler Circuit.
Going from 5/16" to 3/8" Cooler Lines will provide an approximate 43.5% increase in area, that will aid in Cooler flow/ performance.

Hydra-Matic/ GM Power-Train Engineers were pushing GM to make this change to their Vehicles for a few decades...
and finally gave in, around the Mid to Late 1990s. First with Trucks, and then with the Cars as well.

With high-powered Power-Trains... I even go to 1/2" or -8AN Cooler-Lines for PowerGlide and THM400 Units.
In regard to Stock Case (Aluminum) PowerGlides... many of the Cases can have the 1/8 NPT Cooler Ports enlarged...
By drilling, and the tapping for 1/4 NPT Cooler Port Threads. Then add a 1/4 NPT to -6AN Adapter.

Also, try to maintain an ATF temperature in the 160*F to 180*F range.
There are some very good Threads here, regarding adding a Cooler, or going to a stand-alone Cooler...
As well as the use of Electric Cooling Fans.