Most people in the know--and I am certainly not one of them when it comes to
oil--will tell you not to rotate between multi viscosity and single weight oils. Most of the experts on this topic are even more wary of "divergent" multi viscosity oils (10-40 v. 10-30). Most will not recommend using 10-40
oil because it takes so much in terms of additives to get the
oil to protect and, also, flow at those numbers, that lubrication quality becomes more of an issue when using a 10-40 v. 10-30
This comes from a lot of literature on the subject, much of it having been talked about on this forum.