[touringpro]

Originally posted by Cal Cruzer

Viscosity is viscosity no matter what you are measuring, Mobil 1 or pancake syrup. That is why they have the viscosity ratings. It is to measure the flow potential of fluids (I think an engineer could explain this better than I). If Mobil 1 is telling you that the ratings do not apply to them then they have a problem with their oil (not likely) and should not be publishing ratings in viscosity for their products. We have to be able to rely on this information.

Viscosity is a range not an absolute number - and it can vary significantly from brand to brand within the same weight range. From SAE J300 revised June 2001, Engine Oil Classifications (Kinematic Viscosity (cSt) at 100°C):

20: 5.6 min. - 9.2 max.
30: 9.3 min. - 12.4 max.
40: 12.5 min. - 16.2 max.
50: 16.3 min. - 21.8 max.
60: 21.9 min. - 26.0 max.

Mobil1's numbers are as follows:
0W-40: 14.4
0W-30: 10.1
0W-20: 9.0
5W-30: 9.7
10W-30: 9.8
15W-50: 17.4