I know that 10W-40 and 10W-30 are supposed to pour the same (10W) but I noticed from a couple of posts here that people have said that 10W-40 is still a thicker viscosity than 10W-30 in cold temps, is this true? I have been using 10W-40 in a 1987 Mazda B2000 with a 2.0 liter, the owners manual recommends it. Should I switch to a 10W-30 this winter? The temps here rarely get below zero degrees, but we do get lots of snow. Thanks.