after running mobil 1 for a few oil changes, i did get a solid 2mpg increase. and i notice toward the end of the the life of the oil it decreases mpg's. cruising at 70 with a relatively flat grade road i can run at 20mpg, by paper. it drops down a bit when it is time for an oil change. i went 4k miles on the last change.

 

Yea, 4 mpg is a bit extraordinary, get about 250 miles or so into this oil and see where it's at.
I did however see a solid 2 mpg gain in my Jeep Grand Cherokee Overland after putting Royal Purple in the engine and both diffs plus a K&N drop in air filter and it's still showing that on the overhead six weeks later. But it's the first oil change since I bought it and the previous owner was an older couple who had EVERYTHING done at the dealer since day 1, so I'm sure it's the first it's seen a synthetic lube anywhere...

 

Have only had my Dodge for a couple of weeks now so am far from an experton these trucks by any means, but after "feeding the beast" a few timesI am definitelyinterested in any discussion re mileage improvement. However, you noticed a 4-mpgchange in 1 day??? Forgive my lack of faith here, but were you drinking some of the oil?

Sorry Steven, msg was intended for senselesscreationz...my bad.