I went to buy the supplies to change the oil in my '00 2.8. I asked for BMW 5W-40 synthetic, but dealer said they only carry and use BMW 5W-30. I asked about the temperature range on the 5W-30 but just got the canned "this is what we use" answer. So, does anyone know the temperature range on the BMW synthetic 5W-30 and 5W-40 oils. I live in Austin, TX. Is the 5W-30 ok for the extreme heat that we have here?