yeloshak

Had my 2008 S4 Avant almost a year now.
Got it with 55k on it, has about 61k now. Im the third owner.

Started throwing the gas receipts into the console and bored I got an app and punched in the data.
Attached is the plot. My driving is very constant - commute during the week and sits on weekend.

A few trends pop up.
The oscillations in the second half match the station I fill up at - the one at home has 10% ethanol and I get about 10% less MPG. When I fill up closer to work, I get better MPG. My commute length is such that I alternate between filling up at work and at home.

But most concerning is the overall drop from July '13 til now.
You can see a steady trend down from ~17.5 to under 16.

Any ideas where to start looking for things affecting gas mileage??

BoostLad

Couple ideas - these cars are known to go thru fuel filters - if yours has not been changed, I'd replace it. Also, your timing coincides with implementation of winter blends in gas (depending on your region) which hurts gas mileage. I have an 07 with same miles, and have seen mine fall off too.

Just curious (wouldnt affect your issue) - Are you plotting actual mileage (miles div by gals) or what the driver info screen says? I've found a large discrepancy (about 15% or 2-3mpg) between the two, with the computer overstating the actual.

DOALLAR

BoostLad - I'm picking up what your throwing down. With the addition of 10% corn juice in winter gasoline (here in CO), Ive always notice a dip in fuel economy ever since this implementation. Plus a clog FF doesnt help either. Good luck to OP!