Which oil to use?
 

Just got an 05 A8 with about 70K on it and about to change oil and filter. I read the oil change info sticky on this site. But still unclear as to what weight oil to use. Planning on going with Mobil 1 but do I use0w30, 0w40,or 5w40? I live in new England Thanks

0w30, 5w30 or 5w40 are all fine. In colder climate, 40 is thicker than needed. I'd go with one of the first 2. Audi starts you with 0w30, but approves the other 2.

Ok I read somewhere that we were supposed to use the 0w40 and I could not find that in the 5qt mobil 1 jug. So 0w30 is good to use for the 4.2? Thanks

Absolutely...right out of the Audi owner's manual...and what Audi ships them out with.

whats the difference between the 5w40 and 0w30? When I called the dealer, they told me 5w40, but in the manual it states 0w30. What did they change it or something? I just dont want to use the wrong type of oil and shorten the life of my motor. Thanks

5w40 is a hair thicker than 0w30 and is approved by Audi...and acceptable. In colder climate, I would opt for the 0w30 since it would tend to remain thicker from the cold.
5w40 will not hurt anything. Sometimes just a matter of opinion and general climate. In older motors, some use thicker than recommended oil to gain a little more oil pressure and some believe less likely to leak(?)