I regulary used 5W-30 Mobil-1 oil for my A6 4.2-2000. Can I replace with 0W-30??? Thx.

 

Yes, but look for a 40 weight if possible.

 

0W-40 would be best, but 0W-30 won't hurt in the winter. Come summer, back to the OW or 5W-40. If you had a turbo, I would recommend nothing but 0W in the winter.

 

Well, I was just getting ready to say 0W-40 would be better but I remembered seeing this link, and VW now recomends 0W-30 as well for higher performance engines. I still would run 0W-40 but according to this list, that would probably be fine, Here...
http://forums.tdiclub.com/showthread.php?t=129311