Wally Kimble and I drove our wives to Newfoundland from Oregon several years ago.  His then new '06 Patriot Thunder fan never stopped blowing.  When I was in trail, I could see the road dust bellow out!  I recall a discussion that the fan system consumed about 50 hp and the necessary fuel to keep it turning.  It may have been a malfunction, but it seemed normal.  Wally averaged about 6 to 6.5 mpg.