Although the 0W-40 has the "0" designation, it is heavier than the 10W-30 when cold. Because cold start up is the largest threat to engines, wouldn't running a 10W-30 be better than the 0W-40 during the winter? Am I missing something? I use the 0W-40 in my 1997 SAAB 9000 Turbo now, but I need to...