You'll be fine. Though it's not the same engine, I had three 2.5's that logged over 800K miles between them and all I used was 5w-30 for the entire "life" of each engine - year round. Now where I live (eastern VA) does not get below 0*F often - coldest we usually get is mid teens, but we do get over 100*F frequently in the summer.
Your vehicle is a 2002 and unless you have a lifetime extended warranty (or do you?), there are no warranty issues.
