A friend of mine who has a 2000 a4 used 5w-30 full synthetic mobil 1 oil.

Will that ruin his engine? I was trying to tell him that it's suppose to be (x)w-40

 

Yes, it will ruin his engine. NEXT!

Just kidding. He'll be fine, as long as he isn't mixing synthetic with dino oil. where does he live, btw? In the frozen tundra of the upper mid-west, I use Mobil One 0w-40 year round. 5w-30 should be fine, though.

 

we both live in the new england. Im in Rhode Island, he is actually right over the border in MA.

 

Pretty much all of us in my area of NY use 5W30 year-round with no issues, whether synthetic or melted dinosaurs. No problem at all.