Originally Posted by
JohnBurke
Some oils get thicker at low temperatures, or experience an increase in viscosity. Others do not, and are engineered to be less resistant to flow (lower viscosity rating) at lower temperatures to allow them to flow when cold. Hence, multi-viscosity, or multi-grade oil.
They all get thicker in the cold, it's just a question of how much. Multi-vis mitigates that effect.