My son has a 2007 Jetta with a 2.5L engine. The car has 99K miles on it and he drives about 12K a year. We live in Georgia. VW calls for 5W-40 synthetic oil. On his last oil change, he took it to WalMart and I just noticed they put in Castrol HM EB 5W-20. I'm not sure why that put that specific weight oil in there but I'm going to switch him back to 5W-40 on the next change. Any specific recommendations from anyone that owns a similar car? Would there be any benefit to go to a 0W-40 instead? Also, I'm a little confused about high, mid, and low SAPS. Any thoughts about that? Thanks!