Im converting over to royal purple oil but my question is what should i look for when picking the # of the oil for ex. 10-30 or 10-40 etc. ? the car is approaching 40k and its a 2006 a6 quat. 3.2l thanks

 

Your location would make it probably easy to choose the appropriate oil for this time of year.
For example, in Florida probably you can go with 10-30/10-40 all the time. However, in Minnesota, Wisconsin, or Rhode Island I would go with 0-40 or 5-30/40 right now.

http://www.royalpurple.com/motor-oil.html