mathematically it will cause a .009 or so loss in mpg, but a thicker oil may help in hotter temps like here in florida
in hot climate it should provide more protection since at higher temps it should stay a little more thick thus hold its properties better. now if you live in Alaska where it gets extremely cold a thinner oil would be better since its more fluid during cold start upAny difference in protection? I run a lot of miles and sometimes they are very hard miles with my job a small loss of fuel mileage is no big deal to me