Ok, here is the problem first then I will provide the background. I am getting NOWHERE with the dealer so I am turning to you who know something about cars to help me.
Purchased a 2008 5-dr auto trans 2.3L Mazda 3 in late Sept. I put about 400 miles on it in 2 weeks. During the first two weeks, I did almost all city driving and got 21-22 mpg. Highway was like 28, 29 so I was happy as a clam.
Then I had surgery. Car sat for most of 3 weeks unmoved. Once I started driving again, the mileage dropped. My city mileage is about 15 and the highway about 20.
Here is what happened once I stopped driving.
My son took it out once - drove it 5 miles. He did put the parking brake on so tight that I had trouble releasing but I did get it released.
I took it to the dealer. I complained about MPG. They told me nothing was wrong and that it was “winter fuel” and there is nothing they can do about it. They did adjust the brakes but swear nothing was wrong.
I tried putting super unleaded in for a tankful with a can of Chevron Tech Ron - it did run a little better (highway 24) but reverted to the old highway 20 with regular gas.
I drive almost all highway daily (15 miles to work, all turnpike, one traffic light at the end) so I really think it should be getting better mileage.
Periodically, there is a slight burning smell. But the dealer says again there is nothing wrong. Just new car smell 
Car currently has 2500 miles or so.
Any suggestions would be GREATLY appreciated. I gave up my SUV for this little thing to do my bit for better mileage and, geez, I got the same mileage in my 6 cyl SUV.
Thanks!
Karen H from Pittsburgh
It wouldn’t hurt to have someone check the rear parking brake to see if it is dragging for some reason. If it is, that could account for both the burning smell and low mpg.
Burning smell? A new car smell is all that nice carcinogenic outgassing from the plastic, not something burning. Your son’s fun with the parking brake may be causing one or both sides of the parking brake to drag, accounting for the reduced mileage and the smell. If this is a FWD car, jack up the left rear wheel and see if it spins freely. Repeat for the right rear. I’m not sure how you would check for a dragging brake on a RWD car. But it needs to be dealt with ASAP. If the dealer is incompetent, an independent mechanic should be able to diagnose and fix it.
See how the mileage goes when you have 4000 miles on it. It may not be broken in yet and it is winter with worse fuel.
I might add that while I have no idea how you are doing it, I find that many people do not measure mileage very well. Looking at a instrument display of mileage is usually very poor accuracy. Recording the number of gallons added and the miles driven since the last fill up over three or more fill ups usually gives a very accurate number.
I do agree that winter fuel and winter driving conditions do decrease mileage but the drop you are reporting is rather high.