It seems you are entirely incorrect about this if I understand that you believe the axle/propeller shafts turn in 2WD in a vehicle with auto hubs. Feel free to chime in over here... http://www.nissanforums.com/pathfinder/143317-97-pathfinder-4x4-vibration.htmlThe shafts wouldn't turn. The Xterra I had with manual hubs was rated for slightly more mpg.
Yes yes yes!! NPORA wins again! Haha. But this is true. Unlike the 90-95 pathfinders that had autolocking hubs, 96-04 pathy's have drive flanges. This means that whether in 2WD or 4WD, the front axles are always spinning. So yes, adding locking hubs will help MPG. How much is hard to say as I've heard from 1-4 MPG increase, with 1 being the more realistic amount (hey, thats 1 more day I can drive between fill ups!)R50 (96-04) Pathfinders have drive flanges, not auto locking hubs. Drive flanges are ALWAYS connected so you experience a parasitic drag from the front drivetrain in 2WD. Manual locking hubs free up that drag. I have seen at least a 1 mpg increase on both of my Pathfinders.