Hi, 1997 Civic LX, 5 speed, US model.

The owner's manual says my gas tank has 11.9 US Gal. Each time the
needle reached the EMPTY line, I refilled and usually I put 8.5-9
gallons of gas. This time I wanted to try higher octane (to
troubleshoot a pinging problem) and I decided to run just a little bit
longer before I refill. Usually a gas tank lasts 230 miles, this time I
run 260 miles and I was about to stop to the first gas station, when I
run out of gas on the highway. The momentum kept me going, I was able
to take the first exit and there was a gas station, I bought a plastic
gas can and went back to my car, then I drove to the gas station and
filled up. The total amount of gas it took was 9 gallons, 1 in the
plastic can and 8 more when I drove to the pump.

So, from dry empty to full I put 9 gallons. The manual says I have a
gas tank of 11.9 gallons. Almost 3 gallons of gas are unaccounted for.
WHAT IS GOING ON???

Now I realize how close I came to running our of gas, almost each time,
thinking I have so much gas left in the tank. WRONG. Then, I felt like
a moron, running out of gas, pregnant wife waiting in the car, hot and
humid outside, you figure it out... not fun at all. she wants a divorce
now!!!

To add insult to injury, my experiment also failed: the sound that I
thought was pinging is still there, even though I filled up with 93
octane (usually I get 87). True, I drove only 15 miles since the fill
up, maybe it needs some time to clean the pipes and the fuel injector
of the old gas, or perhaps the engine needs a few more miles to adjust
to the new octane, but still, if the sound remains, I wonder what it
is. If it does not go away with 93 octane, then it is not pinging...

weird. I think this car is haunted. and whatever it is, it lives in the
gas tank, it takes up a volume equal to 3 US gallons, and it makes a
sound similar to pinging. Anyone want to buy this car???