I have a 1999 Ford e-150 van with the 4.6l v-8. Ford only recommends 5w-30 oil. I see on this site 10w-30 is more widely recommeded. Should I use 10w-30 in the warm months and 5w-30 in the winter? Does it really matter if I use 10w-30 all year long? Or should I stick with what Ford says? What is the benifit of 5w-30 over 10w-30.