What does 10W30 mean?

Answer 1

When referencing motor oil weight, you are actually referring to the viscosity grade or the tendency of a liquid to flow slowly or quickly. The Society of Automotive Engineers (SAE) developed a grading system to designate the viscosity level of single grade and multigrade motor oils.

In single grade oils, the lower the number, the better it flows at cold temperatures. Likewise, the higher the number, the thicker the oil. In regard to multigrade oils, the first number in the code, such as 10W in SAE 10W-30, means that the oil can still be pumped by the engine at a temperature as low as a single grade 10W oil. A 5W, like in SAE 5W-30, can be pumped at an even lower temperature, and a 0W, like in SAE 0W-30, will pump at the lowest tested temperatures. The W in the designation is commonly thought to represent weight, but in fact stands for Winter. The second number, 30, indicates how well the oil will flow when heated to 100C/212F or higher. there are charts available on the net which give the temp raings for the different oils