Read the Article on using Power steering cooling coils- heres another:
Another possibility is the Automatic Transmission Cooler. On most cars it’s located inside the radiator. If you have a radiator shop nearby, you have a good chance to pick these up in almost any size and shape for next to nothing. They should have lots of them in the scrap pile.
They also come with 2 fittings so you can easily hook it up- I used Automotive steel brake line for mine.
They rarely go bad in the radiator- I personally have a used one out of a GMC 1 ton HD. Dimensions are 12″ X 2.5″ X 1.125″.