I have had 5 or 6 late model MDX’s and now have my second RDX. They will run on regular, mid grade, or premium. I believe that milage is higher with premium, having checked full tank to full tank. All of my 20 plus Honda’s and Acura’s seemed to get better milage after a few thousand miles. YMMV.
This vehicle came with a full tank of gas. Ask you salesman what grade they bought.The window sticker sttaes that the RDX comes with a “full tank of fuel”.