With modern oils is there any reason not to always use the lowest cold rating with the same operating temperature rating oil? I have read that in the past 5 W30 oil had more additive and was less shear stable than 10 W30 but does that still apply today? Also even if my manual doesn't mention it, because it wasn't invented in 1992, is they any reason not to use 0 w30 oil in a car that calls for 5 or 10 W30 oil. It is my understanding that the first number is the viscosity when cold. Why not use the lowest cold rating while keeping the "hot" rating?