I've noticed whenever I fill up with about 11 gallons or so from 1/8 of a tank, my fuel guage goes all the way up. Now if I dont understand correctly the 4th gens tank is 18.5 gallons, so 11 gallons to fill up the tank sounds like my guage is way off. How can I fix this so I can get an accurate reading?

It's not 18.5 gallons.

It's more like 17.5 or 17.

I've been pretty damn close to empty and only managed like 16.75 at most I believe.

Edit: Quick google showed it's 70 liters, which is 18.49 gallons. Wow. Learned something new.

The gauge does not appear to be liner. I've noticed i can go much farther on the first quarter of a tank, and progressively less far on each remaining quarter. So it seems like there is more deflection in the gauge the emptier the tank gets.

I get about 200 miles from full to 1\4 and then another 100-150 on last quarter

i have noticed that i get like 30-40 more miles on the first quarter compared to the last

It is 18.5 gal...

with me its the opposite, I get less and less until I get to 1/4 tank, when I get down to 1/4, I stay on there for a while, usually about 70-80 miles. I'm not sure on the exact number, but its around there, so I'm guessing its natural for the guage to do that and not a calibration issue or something?

no, i fill up the tank and i get anywhere from 260 to 300 miles. it all depends on how you drive maxy, and if you maintain the drive train and what type of gas you use. tires, fluids, etc.,all have a bearing on the gas mileage you get.