I find it odd that so many get worse mileage in the winter. My mileage goes UP in the winter. This could be due to the oxygenation of the gasoline, which can affect mileage by up to 20%. In the winter, the air is denser, therefor you get MORE air into the combustion chamber, this should increase mileage, not decrease it.

 

I live in West Texas and also get better mileage in the summer. I wonder about the "density" of the air....the more dense the air is, the harder the car has to work to push through it....the less dense (a hot summer day) the easier it is to push through it. (Just like air is less dense than water...it's a lot easier to run through the air than through water)

I'm not sure of all the reasons, but my mileage is better on hot days than on cold days.

 

Colorado Springs. Just got my worst tank, 44.1 All summer I was getting 53-56. Then came snow tires, winter gas & this week @!#$@ snow @#$%@. If cold air hurts gm - why can't the intake be routed around the exhaust to heat it up?

 

just found this

http://www.cleanmpg.com/forums/showthread.php?t=17560

 

since the temps have been below 80 during the last few weeks, my mileage has gone up by 20%