03-17-2014, 09:02 PM
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Join Date: Feb 2007
Location: Colorado Springs,
CO
Cobra Make, Engine: Backdraft, supercharged Coyote
Posts: 2,453
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Quote:
Originally Posted by 347stroker
Again I'm learning what I need to know about oils. The first number is the cold viscosity and the second number is the hot viscosity. Please correct me if I'm wrong or steer me to a site that explains it. To
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Yes, that's essentially correct. Keep in mind that viscosity is highly dependent on temperature, and is measured at standard temp. As the temp goes up, the viscosity goes down.
The second number is the viscosity at operating temp. For lab purposes, that's 100*C. That doesn't mean the oil will have a viscosity of 40 at operating temp, though. What it really means is that if you had a 40wt oil at standard temp, and then heated it to 100*C, this is what it would be like. The actual cST viscosity at 100*C is somewhere around 15.
A UOA will report that for you. As the oil wears out, the viscosity drops.
Used Oil Analysis - Bob is the Oil Guy - Bob is the Oil Guy is a great place to study tribology.
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