Quote Originally Posted by Mr. KiDD
the only way to do it RIGHT is to fill it all the way till it STOPS. fill it up an check how many GALLONS you paid for.

now, reset the TRIP odometer. Usually civics have 11 gallon tanks. Look in your owners manual to be sure.

drive it. You should be getting AT MINIMUM 25-30mpg. when you get to halfway note your mileage and divide it by half the tank. when you get to "E" divide your mileage by 11.

that will tell you MILE PER GALLON.

if its anything under 20MPG you have something seriously wrong or your gauge is Way off which is possible.

for reference, $20 in my silvia BARELY gets me half a tank, BARELY.
I always keep a count on my mileage b/c I like to drive on E somtimes =X Haha.

When I put $20, I usually get about 200 miles before the light comes on...that's why I'm so concerned b/c I literally just put $20.00 and I've only driven 42 miles and it's already on a quarter tank.........!!!!