Chemically, I do not think that would happen. However it might be of interest to compare all three VOA's. (to see if the blending would inadvertantly do what you hope)
Before I give my example, it all gets down to specifications.
http://www.mobil.com/USA-English/Lubes/PDS/GLXXENPVLMOMobil_1_Truck_SUV_5W-40.asp
In my application VW Jetta TDI, the reason for the 5w40 is the viscosity is a buffer device for very high pressure (applied to camshaft etc), diesel operation. 5w30 (even in Mobil One has been shown in TDI test engines to not provide as good a buffer, thus hastening microsopic wear.
This is NOT to say that subsequent 5w30 oils that (importantly) meet the new VW standards do not work but truly in so far as longevity is concerned the verdict is still out on them.
So obviously the implication is since Mobil One Truck and Suv 5w40 can meet diesel standards which are much tougher on oil than say gassers, it can meet the truck andsuv/gasser as well as suv diesel specifications, and of course it does meet most.
There is also a real danger in speaking of (how do I say this )loss in the translation between standards here. So for example one standard might apply in HK and another in the USA.
I know this is true in Euro. In Euro Mobil One products for say VW costs 10-15 USA dollars per quart!! M1T&Suv costs at most 5. etc etc.
