[Ecobalt]

Originally Posted by 2007 ion2

0 (cold "weight")W 30 (hot "weight"), the 0 is only under certain conditions, and when it warms up, 0W30, 5W30, 10W30, and straight 30 weight oil, all have the same properties (all other variables eliminated). I am a mechanic, went to a university for it and everything, most of the car driving public would believe as you do, but you are mistaken.

0W-30 means that the oil still has the viscosity of 30W oil, even when it has reached operating temperature.

Which 30 Weight Oil Do I Use, 0W-30, 5W-30 or 10W-30?
We get asked this question so often that we have included this special page dedicated exclusively to answering the question.

AMSOIL 0W-30, 5W-30 and 10W-30 synthetic motor oils are ALL 30 weight oils. The answer is that ANY one can be used regardless if your vehicle owners manual says to use, for example, a 5W-30. "W" means winter. In winter weather the 0W oil will flow like a 0W oil, and the 5W will flow like a 5W oil and a 10W will flow like a 10W oil just until the engine warms up. In order to understand the differences one has to first understand that the numerical values given to these various weight oils are strictly empirical numbers. For example, 0W does not mean that the oil has no weight. That is one of the reasons why we say it is strictly an empirical number.

In order to determine the differences between the three oils one has to look at the kinematic viscosity of each lubricant. The kinematic viscosity is essentially the amount of time, in centistokes, that it takes for a specified volume

of the lubricant to flow through a fixed diameter orifice at a given temperature.

Let's compare the kinematic viscosity of the three AMSOIL lubricants

AMSOIL 0W-30 is 57.3 cST @ 40 °C, & 11.3 cST @ 100 °C

AMSOIL 5W-30 is 59.5 cST @ 40 °C, & 11.7 cST @ 100 °C

AMSOIL 10W-30 is 66.1 cST @ 40 °C, & 11.7 cST @ 100 °C

As you can see from the data above the kinematic viscosities are extremely close. Therefore, whether you use the 0W-30, 5W-30 or the 10W-30 is strictly a matter of choice. With the small differences in kinematic viscosity you would be hard-pressed to detect these differences on initial engine start-up without specialized engine test equipment.
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Which Oil Do I Use? 0W30? 5W30? 10W30?