6 Answers

Standards for identifying the viscosity characteristics of engine oil have been made by the SAE. The 5W-40 part of the symbol is actually just a name. The W part of the name is an indicator of low temperature viscosity properties while the 40 part of the name is an indicator of the high temperature or operating viscosity properties. The numbers are just relative indicators to help the consumer. In other words, a 5W oil does not have a viscosity of 5, nor does a 40 weight oil have a viscosity of 40. What the numbers do mean is that the viscosity characteristics of a 5W oil are lower than that of a 10W oil. As well, a 40 weight oil has lower viscosity properties than a 50 weight oil.

Math question right? I came up with 5W-10

5W and 10W refers to a quantity of oil and is its weight. The last numbers refer to it viscosity, How well the oil holds together at a specific heat or thickens at a low temperature..

The viscosity of oil is measured by its ability to flow through a graded hole at a certain temperature ~ W actually stands for winter and is a general expression of its ability to work at lower temperature while the 2nd number is it ability to work at higher temperature

03/11/2011-11:10 am

I have been told that 10W-50 is recommended for older cars.
Professor

5w-40 type oils are mo ere stable in changing temps as compared to say 20 wt, 30 wt, 40 wt, etc.
supposedly the characteristics of 5w-20 is that when hot it has the viscosity of 20 wt oil, and when cold it has the viscosity of 20 wt oil.

in other words the multi wt oil is less afected by temp changes.