HT750DRD Oil Cooler?

Howdy y'all I know this is no RV, but it is an Allison. I have a HT750DRD in a 85' Mack it currently uses a Hayden air to oil cooler that measures 36x30x1.5 and cools about 100,000 to 164,000 BTU/HR and flowing about 15 GPM.
This air to oil cooler works fine in hot weather but in cold weather the trans never gets above 100 degrees working it very hard. I have a water to oil cooler from a Allison HD4060 Pierce fire truck it flows 20 GPM but I do not know what the BTU/HR is. It looks like it will work and is an easy hook up, but will it cool enough?
HT750DRD Oil Cooler?

Sounds like your playing with fire. I would use the Hayden in the summer and cover up half of it in the winter or as much as you have to to get the temp up to 170. A small piece of cardboard or thin piece of wood should do the trick.