Ive been using 10w-30 since day 1, was on rockauto looking at oil prices. I know Ford had a TSB to use 5w-20. Any reason to use 5w-20?

 

I've run both in mine and never had any oil issues, maybe they found the thinner oil just lubes a bit better

 

I changed to 10 w 30 last week and haven't had any issues. I was tempted to use 10w40, but I will wait and see how the 10 w 30 does long-term.

 

Unless you live in AZ or other hot climate states, 10W40 is overkill. 10W30 is best for states that have 4 seasons. But be aware if you drive your car during winter where it snows, you'll want 5W30 in it during those cold months.