poor fuel mileage

[stanzz]

I've been getting very poor mileage for quite a while now. I've done the basic tune-up, changed the O2 and coolant temp. sensors. The car idles and runs fine. I've had the car in twice to the dealer and they haven't found a problem. There aren't any ECU codes. Any advice?

[wamQ45]

Not enough information.

MakeModelMilageMPGs

[elwesso]

This needs to be moved into the NISSAN ONLINE MECHANIC, as it says you have an altima...... If thats wrong please say so.....

But, in answer to your question... You definitely wont see as good of gas mileage in the winter because of the oxygenated fuels.... While I cant give you many specifics, its not as good quality as summer gas (stuff in it to keep it good while its cold) and it doesnt produce as much power.....