Quote:
Originally Posted by juliusmichaelhonrada
But im using 10w-40 oil , i thought when cold its weighted as 10 , and when at 100 celsius it becomes a 40 weighted oil? :)
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Yes, a multi-grade oil acts like different weights at different temperatures. However, those weights are not set viscosity numbers, they're grades. It's not "10 viscosity units at 0° and 40 viscosity units at 100°", it's "viscosity units equal to 10 weight at 0° and viscosity units equal to 40 weight at 100°".
Here's an example. 10W-30 acts like 10 in the cold and 30 when it's hot. But the actual viscosity measurement of either one in the cold is much higher than the viscosity of either one at operating temperature.
The point of a multi-grade oil is to give you the benefits of a lower weight oil in the cold and a higher weight when it's hot. This means it flows better when it's cold (without getting too thin when it's hot) and protects better when it's hot (without being too thick to pump when it's cold).