My Posts: All Forum Topic
We don't what the viscosity of the initial oils are, add to that one may be going by weight the other by volume. The lower weight oil will have less internal drag on the engine, (one reason you can lessen the fuel intake), it will also thin quicker the higher the temperatures elevate.
This also has a tuning effect, as well as the oil being almost non compressible. There is also a steady state and a transient state that has different fuel requirements. I think this is not that simple an answer. Oils effect the the engine but never to the extent the combustible product effects the outcome. The thinner oil can not carry away as much heat as a thicker oil so you introduce less fuel generate less heat and the engine is happy again. The thicker oil will carry away more heat so you can run more combustible product each stroke.