QUOTE (trini tuner @ Nov 7 2009, 12:35 PM)

im switching over to the purple power but what do the #'s mean? ex 15-30... 10-40.... i know it has to do with the makeup of the oil but what should i consider when I am choosing an oil for my car? IM also posting a thread on an audi forum but I really respect your guys' opinions so I wanna hear from you all as well. Thanks
in south florida i would go with either 5-30 for optimal fuel performance and fuel efficiency or 5-40 (or 10-40) for spirited driving. You really dont need 5w low end because florida temps would never drop below -10F, but the thinner the oil the faster your engine will get lubricated.
I wouldn't go over 40 on the high end, unless you're running FI and NOS i doubt your engine would ever reach high enough temps where 40+ is needed. The higher the number the more crap is added to oil to make it chemically resistant to heat.