Hi -

My '09 has ~47,200K and I have recently noticed a drop in my fuel efficiency.

I was previously averaging 20 mpg. My last 7 fill ups have been the following:

November - December:

20.0 mpg
18.8 mpg
18.9 mpg
18.9 mpg
17.1 mpg
21.1 mpg
*Got new tires, air filter, balanced, rotated, added fuel injector cleaner.
17.8 mpg

Previous to this all my fill ups have been 20.1 - 20.8 MPG. All highway driving, ~70 mph, ~60 miles a day. Currently I am at a half tank with 174 miles driven.

Any ideas for the quick drop off? Is this a case of "winter gas"? Fuel economy is tracked with aCar for Android.

 

Yes "winter blend gas" can account for 1.5-2.0 mpg,
the new tires with "new friction factor" can also
contribute even with a great 4 wheel alignment.

 

i have been told from people that know. that gasoline blends are changed as often as 2 week time. they guess at what the air temps are going be in the next weeks. and adjust the gas blend to the new temps. but if the temps are off, it can cause trouble. this happened to me. some times the fuel blender gets the reid vapor pressure of gasoline off to. back in the 80s chrysler found out this was happening, causing driviabalty trouble.