Greg and Peggy,
Welcome to the forum! I think you'll find that you can get a lot of your Alpine answers right here.
I did a Find on the words: hydraulic fan, in this forum, and there were 23 hits. Note that the Find button is just a half inch above Peggy's name on your Post.
The answer that kind of sticks out is this one: HYDRAULIC RADIATOR FAN MOTOR
In that Post, the owner of a 2001 Alpine says his Hydraulic Radiator Fan Motor is a: Sauer Danfuss hydraulic motor that runs the cooling fan for the radiator, Model # TAM22-90/26,5C107.
We also have a 2004 but I'm 3000 miles away from the Alpine right now so can't be of much assistance by looking on ours.