Considering that I am currently at 12,750
miles & counting..... and I have changed my oil twice - here are my results.
1st Oil Change was at 5500 miles
Tank Prior - 30.35mpg
Tank After - 34.16mpg 3.81mpg increase
2nd Oil Change was at 11900 miles
Tank Prior - 31.37mpg
Tank After - 34.90mpg 3.53mpg increase
Conclusions - statistically it is too early to tell but the first tank after an oil change looks to yield better gas mileage. Less friction with the oil. We should all keep an eye on this. (My driving habits were the same for the priors / the afters & temps were even.)
One may say that getting more frequent oil changes would give better gas mileage. Perhaps. Jiffy Lube wants you to change every 3000 miles which in my case would be every 6 weeks.
However, changing your oil prior to its useful life in my view is wasteful. Getting better gas mileage is great but not at the expense of changing your oil more frequently. The greater goal is still the environment and saving money. (You can pick the order.)
To firenurse - hope you recover from the injury soon - I was expecting you to pass me on your next fillup or two - you were coming on strong.