I've gotten 16 gal into mine when the car was parked on a slope. If you have ever had the back seat out so you can see the top of the tank, the VX/CX gas tank has a hump with a lot of space in the tank above the level of the filler line so it still has a lot of air in it even when it has liquid visible at the gas cap opening when filling it on a level surface.
Stock, my car typically reached 240 miles at the 1/2 tank mark, but since I modified it, now reaches 400 miles at the half mark.
yeah I noticed a lot of gas tanks are like that, however I would hope there is a reason to that because on my LS400, when I took out the fuel pump to inspect it, I saw that the tank maximum height was actually significantly higher than where the fuel filler goes. Weird stuff but I'm glad you observed something similar with your civic.
To Viperguy's remarks;
Any chance you've been smelling gas around the car recently?
I live less than a block from a 24 hour filling station. I've been ignoring the very very slight fuel odor intermittently around my car. I was doing some other maintenance two days ago and noticed dark spots around the tank straps in the undercoating on the tank.
I dropped the tank to find rust holes I could put a flat bladed screwdriver through (with some force, they were pin-holes before I scraped at it) at the base of the half-moon shape of the rear of the tank. At first it looked like the rear seam, but it was actually the area above that tucked under the car. I also replaced the filler neck clamps with new ones. I'll give an updated FE report soon. I usually get 52-53mpg on fuel ups. I drive 60mph on the highway, 45psi tires, full grille block, etc. I'm hoping this brings up my numbers! I once got 65mpg on a one-way trip of about 100 miles. I fueled up before I left, and filled up immediately upon getting home. This tells me time is a factor. (the more time I leave a full tank in the car, the worse my FE number would be)
Check your tank, lines, etc. Try to move your injectors while the car is running and see fuel spray out. Replace those seals too!
Worth a shot, eh?
Yea my VX is solid and has no fuel leak anywhere. It'a a California car that I turned into a federal so there's no rust on it. I usually average around 46-47 mpg only. My VX is kind of wired, I would usually get around 42-44 mpg on one tank and the next tank I would get 50-53 mpg LOL ( same driving style ). If I fill it up and it takes 80-90 miles before I see the gas guage start to drop than I usually get 50+ mpg. If I only get 40-50 miles before I see than gas guage drop than I will certainly get around low 40's. I drive 60-70 on the hwy though and I have my tires 170/75/13 at 41psi. Overall i'm happy with my VX, I think 45mpg is OK for me. Constant 50+ mpg like your would be nice though.
I'm pretty sure that the 1992 CX and VX share the DX and Si fuel tank, which is 11.9 gallons. I know that at least 1994 and 1995 CX and VX models have a 10-gallon tank, and I'm pretty sure that the 1993 models do, too.
Google Honda Civic VX Specifications or Capacities. You may get what you're looking for.
The rust I found on mine was hidden on the top side of the tank. There is little to no rust anywhere on the undercarriage, so I figured there wouldn't be on that tank. When I dropped it, it was clear moisture was able to pool near the back (from condensation?) and ate away at the undercoating.
Of course, I would not have noticed this save the discoloration of the undercoating.
Try driving 60 on the highway for one tank. You'll be impressed with the results. I was getting about what you are getting until I started to do that.