Visc at 40 c and 100c

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May 25, 2003
Quebec Canada
When I look at the viscosity chart on the front page I can see where my oil is on the scale at 100c, but when I look at the visc at 40 c the number that I have for my oil doesn't make sense. 65.3 is base # for my oil,at 40c the uoa say 54.1(abn) 10.5 is the # for my oil at 100c , the uoa say 9.6 Now I can understand that my oil thin a bit at 100c. But if I looked at the chart for 40c 65.3 represent a 20w instead of a 10w ???????
Engine oil viscosity rating is governed by SAE J300. I specifies viscosity at 100C and at sub zero temperatures that vary accoding to what viscosity the oil is. 40C viscosities are referance only. They may be interesting but don't tell you what the oil viscosity really is at sub zero temperatures.
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