a shitty oil gets frothy, oil grade has nothing to do with it

the first number is the "viscosity" at ambient temperature, the lower the number the easier it flows

people don't understand oil, they think it thins out as it warms up, but it thickens as it cools down

your second number is the "viscosity" at running temp, and the numbers work the same as the cold number

if you really want the deal on oil, read this
FerrariChat.com - FAQ: Motor Oil Articles by Dr. Ali E. Haas (AEHaas)