Fuel economy savings with 10w30?

[Danny26]

Wondering if anyone on here has seen any real difference in fuel economy running 10w30 vs 5w40. I've always ran 15w40 or 5w40 synthetic in diesels and trying to decide what to run in my 6.7... seems like the new trend is to run 10w30...

 

[Ragu9000]

its not a trend. its what the motor calls for during regular use (not heavy towing often)