Oil Changes, Gas Mileage, and my Unreliable Gut

Kia recommends that I get the oil in my 2009 Rio changed every 7,500 miles. But, anecdotally, it seemed that I always got better gas mileage right after an oil change than I did right before I was due for another one. So, I got to wondering - if an oil change costs $20, but saves me a few MPGs, is it cheaper overall to change my oil sooner than 7,500 miles? If so, where's the optimal point?

So, I got all ready to do some fancy math, and began tracking my gas mileage between two oil changes... And this is what I found:

gas mileage graph

This is why anecdotal evidence is unreliable.

At least based on this one oil change cycle, my gas mileage theory was 100% imagination. I should stick to oil changes at 7,500 mile intervals.

Of course, this is really a sample of only a single oil change cycle. It started in summer and went into winter, so winter fuel blends came out (which generally have slightly higher MPGs), and I presumably used the A/C less (though my defrost requires my A/C to be on, and I use the defrost a lot). There may be other complicating factors as well. So, I plan to track this all over again and re-visit after my next oil change cycle... because gut feelings die hard.