I have about 1000 miles to go before my 2nd oil change in my '98 A4 1.8T. For the first change, I had them put in Mobil 1 15W-50. This oil change will probably take me most of the way through the winter(I live near Boston). Should I still use 15W-50 or should I go to a lighter weight? What do turbo owners on the list do in the winter? Thanks Paul Wilson