I have an 89 LX sedan auto tranny and I get about 305 to 320 miles off a full tank. I don't know how accurate my gas guage is and I don't have a low fuel light so I fill up when it gets really low.

I'm wondering what the typical range is for an automatic civic.
I dug up some old logs showing up to 400miles off a full tank when my dad drove the car.

It might also be that he drove it really slow, but my car is so slow that if I don't if I don't press the gas a bit (not flooring) people are almost ready to start honking. It's not hesitation slow either, it's D15 92hp slow. It's decent, and it's been relatively reliable, but in heavier traffic where I need accelleration I almost have to floor it.

I just changed the spark plugs as it needed new ones. Will this help the mpg any?