I've seen my gas gauge fluctuate by 1/8th of a tank or more. The needle seems to bounce all over the place and I usually just go by the odometer and I don't start worrying until I've driven about 40 miles with the gas light on. Do you remember the last time you filled it up if you put in less gas than you expected? You could be starting to have the problem with the fuel filler neck where it doesn't release pressure and shuts off the filler too early.
I've been tracking my fill ups on my palm with
this *yes yes sound the geek alarm
* but it really helps because I can see my MPG right away when I enter that fill up. It has a ton of other cool features, I'd really recommend it to anyone who has a palm.
I usually get 21-23 normal driving, 25-27 if all highway.
-CtrAltDel
