on my 97 civic lx 1.6 sohc nonvtec, i get 300mi a tank, 12 gal. that seem right? it should be 360 no? 30x12 is 360. i checked it and it says 30mpg. i did get 34 once.

 

it wont run all the way dry
in my EG it would be all the way empty like the car had problems starting empty and still have 2 gallons left in the tank/lines

 

so it runs out of gas w/ 2 gal left? y do they do that?

 

yes
theres about 1 gal left in the lines and when theres about 1 gal left in the tank it starts getting too low for the fuel pump to pick it up safely (if it goes lower it can damage the pump) so they set that mark to be empty from the factory

 

You should be basing this on the amount it takes to refill the tank: the number of gallons you buy at the pump. The rated tank capacity is not important. It is also useful to keep records and make an average over more than one tank.

There aren't many things to "tune up" on a Civic, but the big one that can kill your mileage though it will seem to be running OK- is the spark timing.

Also, this is hard to do on a stock Civic, but avoid pressing the gas pedal all the way to the floor as much as possible. Mileage will be considerably better.

 

if you are getting 300 miles to a full tank, that's not good unless you are in constant stop and go traffic. I get roughly 330-350 per fill up usually in the 9.8 - 10.2 gallon range. This comes out to roughly 32-34 mpg. this is with a mix of suburban and highway driving.

as others have said, you need to start keep records and reset your trip meter everytime you fill up the gas. I've noticed that if a gas station has a slope, it affects the fill up amount. So I try to go to the same gas pump everytime for continuity.

I have also recently started to shift sooner (obviously only applies to manual trans) so that by the time I'm around 35 mph, I am in 5th gear. This seems to keep my rpms low and thereby save some gas that way.