I think it should improve...the first two weeks after I bought my Mustang the mileage
was terrible. That is probably mostly from enjoying the power a little too much
But, as mentioned elsewhere in this thread, most of your milage has to
do with how you drive!
http://ecomodder.com/
I try my best at 'Drive without Brakes' and have really paid as much
attention as possilbe to tire-pressure, any extra junk in my car and
keeping the speeds lower on the highway.
As an example, I went over the Island last weekend, and the round trip I averaged 7.9 l/100km (almost 30mpg's i think)... I kept my speed on the highway right around 90-100kmh(just under 60mph).
Three weeks ago I did the same trip and averaged 10.1... It was from accellerating too fast and doin 140kmh plus pretty much the whole way up the island (speed limit is 110kmh).
Now I've really learned to do all the things that make my gas get me
that much farther(Over the last three tanks I've averaged just under 10l/100km in 80% city driving), so that when I want to step into it I don't have to
worry about the gas-gauge plunging.
The most important piece of the mileage component is the person driving!