Which one is the right oil for my car? 5W-30, 0W-30 what does it all mean?Viscosity Viscosity Viscosity The title of the oil is meant to communicate the type & thickness of the oil at different temperatures (having the correct thickness a.k.a. viscosity is what this article will be mostly about). The W in the name 5W-30 standards for Winter and simply means this oil has been tested at colder temperatures.  (Oils without the W in their name i.e. SAE 30 have not been tested for cold weather performance. At normal operating temperatures (210°F)  5W-30 and 10W-30 will both flow at a SAE viscosity of 30, but under much colder temperatures 5W-30 will flow at an SAE viscosity of 5.   10W-30 will flow at an SAE viscosity of 10.  0-W30 will flow with a viscosity of zero in cold t ... read more