First I'd like to say that I'm new to the site and hats off to everyone that is a part of this site....Full of great advice. My question is that I currently own a 1999 ML430 with 46k I've been changing my own oil every 5k with Mobil1 0w40w. I live in NY and it's about to get very cold, well below 0 degrees. Should I be changing oil weights in the winter? This is my first winter with the truck and I'm not sure if I should continue to use the 0w40w oil. I believe that Mercedes recommends to use the 0w40w all year. Any insight would be truly appreciated.