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Discussion Starter #1
So yes another oil topic. The only reason why I will post this is because there is so much false information about it.

I talked to my coworkers and none of the answers were right. The question is how does an oil rated at 10w when cold become 30 when hot. This means the oil thickens when hot. Or assumable..

I looked it up and plenty of website said oil was designed to be thin as cold and thick as warm... Problem solved..

That didn't make any sense to me... How could anything become thicker as heated? They said additives.

Long story short.. The cold (w at the end of the number) is different then the numbers without a w.

I will explain there is two different test while related are on two different scales. The first is "w" rating which means the maximum force it takes to move the pump at set temp. There is a maximum but not a minimum.

The second is what we all think about a flow of oil. The test is this oil flows thru a tube hot. The faster it flows the low the rating.. This test has between this and this is this weight.

Only point I have it to understand that the w weight has no direct compersion to the none w weight... Two different unit of measurements are involved.
 

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The two ratings are for two different temperatures. 32F for the low end 200F for the high end.


A 10w30 would have a viscosity of a 10w oil at 32F and the viscosity of a 30w oil at 200F. And yes it is thinner at 200F than at 10F.
 

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Discussion Starter #3
Actually the low temp is tested at different temperatures for different ratings. 25w is -10c and can't exceed 13000 cP. While 0w is tested at -35c and can't exceed 6200 cP. See miss information.
 

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A 10w30 would have a equal to or less than pumping pressure of 7000cP at -25c for 10w. The 30 would have a flow rate at 100c of between 9.3 and 12.5cSt. Two different test and scales. The two numbers are not related.
 

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Discussion Starter #5
For those who want to dig deeper in this rat hole:
The "w" uses Dynamic (absolute) Viscosity
Absolute viscosity - coefficient of absolute viscosity - is a measure of internal resistance. Dynamic (absolute) viscosity is the tangential force per unit area required to move one horizontal plane with respect to an other plane - at an unit velocity - when maintaining an unit distance apart in the fluid.

While the "hot" uses Kinematic Viscosity
Kinematic viscosity is the ratio of - absolute (or dynamic) viscosity to density - a quantity in which no force is involved. Kinematic viscosity can be obtained by dividing the absolute viscosity of a fluid with the fluid mass density like.

Stole from https://www.engineeringtoolbox.com/amp/dynamic-absolute-kinematic-viscosity-d_412.html
 
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