DD 8V71 What Oil?

I was seaching on the web for info on what type oil to use in my DD 8v71. I was planning on using Shell Rotella 15-40 but a bus conversion site I found said not to use multi grade oil in these engines. They said to use straight 40 weight and that it was getting hard to find. I would like to use Rotella 15-40 because I always have it on hand for my work truck. And how many gallons does this motor take? Thanks Mike

Rotella oil is available in 10, 20W20, 30 and 40. All of the mechanics that I have talked to about the 6V71 and 8V71 say to stay away from the multi weight oils. The 8V71 takes 7 gallons (28 qts) plus 1.5 qts to fill the filter.