january 2009 i averaged 29 mpg.

january 2010 i've averaged 29 mpg.

july-august 2009 i averaged 32.2 mpg

all mixed driving in new jersey.

 

It's not scientific, but I'm also down a couple mpg the last two tanks. I think it's also a lot of long weekends with frequent trips to the grocery store.

 

last tank i got 21 mpg. compared to the summer where i average close to 29. this is almost 100% city driving.

 

I lost a few but still have respectable numbers. My overall didn't fluctuate too much in two years.

 

Too many variables. Where you are, how cold it is and length of trips makes a big difference. How much "idling to warm it up" before going also plays a factor.

 

Some of it may be due to "winter gas" formulation. I've always lost fuel economy in wintertime, no matter what car I've owned.

 

I once read it was due to the EGR valve. Upon start till the car warms up the EGR valve is open. Once the engine warms up the EGR valve closes. While open the engine gets poorer gas mileage. In the winter it takes much longer for the engine to warm up causing poorer MPG.

When I had my Yaris it had the same problem. In the winter I would get 31-33 MPG compared to the 35-40 MPG during the summer. It all boils down to the temperature outside.

Correct me if I am wrong here.

 

I lose a lot too. You can see the trend great in my chart on fuelly.

The Fit M/T (Honda Fit) | Fuelly

I'm in Michigan. In some ways, I think we have about the biggest extremes between summer and winter weather of any area in the country.

I got a high of over 38 in July. This month I'm down to 31.

Things that I think affect it (besides just the obvious cold temps):
-I keep my tires at slightly lower psi to get better snow traction
-I can't accelerate with as much low rpm open throttle, so I lose some efficiency there
-Coasting for moderate pulse and glide is hard on snowy and pothole filled roads (you lose speed real quick)
-I'm running the defroster almost all the time lately, so the A/C compressor is running too (I really ought to break down and do the wire-pulling mod to stop this sometime soon)
-Winter blend gasoline (plus 10% ethanol at the station closest to where I live)
-It's been windy here a lot this winter so far