Gas: CarTank & Pump Questions

My 2000 Honda Civic specs a 45 Liter (11.889 Gallon) gas tank.

Many times I have been well below “Empty” on the gas gauge, yet I never remember filling the tank above say 10.5ish gallons …

A. How much gas is required to keep a Honda Civic (just to preclude the inevitable “it depends on the type of car” answer) running? For instance : could my car still run on .5 of a gallon or .25 of a gallon? Does the tank have to be literally bone dry to run out of gas?

B. Does my tank actually hold 11.889 gallons of gas as spec’ed or might it vary? I ask because I have been so empty there is no where else for the gauge to go. Yet, as I said, it never seems to have ever taken more that 10.5ish gallons.

**C. ** Is it possible the gas pumps are somehow incorrectly counting what is going into my car? That seems illogical because it could mean I am getting 11 gallons of gas but the pumps is only registering 10.5 going in - seems unlikely but I wanted to ask as a possibility.

A)It shouldn’t matter how much gas is in the tank as long as the engine is getting gas. On second thought, check to see what your manual says about running out of gas. Some manuals will tell you to add at least X gallons (or 1/x of a gallon as the case me be) to get it up and running again. That might be what you’re looking for, but that might just be the amount it takes to reprime the fuel line.

B)First, if you haven’t run out of gas, you really can’t say how much it takes to fill it up at the pump since you’re not filling it from zero to capacity. Second, that extra gallon is going to be sitting in the bottom below the the pump inlet. If the pump took every last drop of gas you’d wind up with alot of setiment in your engine. It’s designed like that to protect your car. (Although I’m still waiting for Mythbusters to confirm that one).

C) All most certainly not. Next time you fill up, look for a seal on the pump somewhere that says “Weights and Measures.” The city/county/state/whatever comes around once in a while (usually without notice) and checks the pumps to make sure they are accurate. I’m sure there’s some tolerance, but not off by over a gallon at 10 gallons.

I think what it comes down to is that you have to remember two things. First since you’re not getting gas when your tank is EMPTY it’s not going to fill to the spec, second, even if you run out there’s still some left in the tank.
Also I’m sure the gauge does bottom out before you run out of gas.

Oh one more think, remember that the spec in the manual is the acutal volume of the tank, not the ‘working’ volume.

I think the most likely explanation is that there is still gas in the tank even when it’s reading empty. I don’t believe the dash gauges are all that finely calibrated, and are intended to give you more of an idea of how much gas there is rather than a fixed, firm amount. Additionally, I’ve been told that there is a point beyond which the gauging device in the tank can’t read anymore, even though there may be a gallon or so left in there, so it just reads empty.

My unsolicited advice is to just fill it when it gets close to empty and not take chances. Once the needle pegs at E, it isn’t hard to forget just how long it’s been sitting on that line and misjudge how much time you have to get to a gas station.

:smack: One more thing. Even when you fill your tank all the way, squeze every little bit you can into it. It’s designed to keep some space up at the top for vapors, and so the the liquid can expand/contract with the weather.

There’s supposed to be a “don’t” in there, right?

Very true, on my car I get 200 miles out of the first ‘half’ and about 100 out of the second. The gauge doesn’t take tank geometry into consideration. At least not in a Cavalier. For me though, I just use the odometer. Reset it when I tank up, once it hits 300 I’d better start thinking about getting gas real soon. I learned that trick when I had a car with a bad gauge.

No. It wasn’t a suggestion. Let me rephrase it. Even when you squeeze every last…

Got it.

I was very low on gas, let me rephrase that, I was very very low on gas, the gage hit new and nerve racking lows. Then finally there was a gas station up the next hill. I started up that hill then stalled out due to no gas. Not being a good place to leave the car, I decided to coast down in reverse to the bottom of the hill, which had some parking spots available.

After actually paralell parking on momentum, I thought the angle might have something to do with it, so I tryed restarting it, which it did. I ‘unparked’ then backed up further, then took a run at the hill, when I get about 1/2 way up I stalled out again, but made it to the top and coasted right up to the pump.

The moral of the story: You could still have gas in your tank and not be able to use it.

Reminds me of a time when I was out with a friend whose father called him and asked him to come help him with the car, which was stalled outside a bar. The car was parked at a steep angle - the left side of the car being a good deal higher than the right side. They tried to start it, fiddled around under the hood - no luck. Me being a sillly girl, they didn’t listen to me when I wondered if the problem wasn’t that there wasn’t enough gas, and that the angle was preventing what gas there was from making it to the pump. They towed it home, and the father, on a whim, decided to try it again. Sure enough, it started, the gauge was pretty much on E, and I got to stick my tongue out at the macho men :wink:

Published gas tank volumes are nominal figures.

You run out of gas when the fuel pick-up tube is no longer surrounded by liquid. There is still some liquid gas in the tank, but it’s not accessible.

Dash gauges are not precision instruments. This is almost certainly the heart of your confusion. If you want to know where the needle will be when you run out of gas, you have to run out of gas to observe it. This will vary from car to car. It’s not recommended, as it’s stressful on the fuel pump to try to suck air.

Service station gasoline pump meters are precision devices, and as mentioned are tested and calibrated annually by a government agency.

And just to clear up any confusion, when filling up, stop when the automatic click-off operates. There’s really nothing to be gained from getting a little more gas in the tank, and there’s some risk of messing up evaporative controls.

Well sometimes there is. At one time I had to commute about 1.5 hrs each way - with only 1 convient gas station on the entire route (near my house at the time). Filling up to the ‘click off’ ment having to get gas every 2 days, but ‘forcing’ in a little extra gas would mean filling up every 3 days.

If you want precision measurement, buy a Scangauge. Costs around $125, but mine predicted how much gas I’d need at my last fill-up to the 10th of a gallon.

Do not try to run the tank dry on a modern car with an electric in-tank fuel pump unless you have $250—$500 burning holes in your pocket.

These pumps are powerful enough to pull a vacuum, collapse their intake screens, and then burn themselves up trying to suck gas through collapsed screens.

My daughter learned this the hard way about 3 weeks ago.

I’m sure this is what you told, but I have my doubts about the truthfullness of what you where told.
Electric pumps in reality don’t suck worth a damn, but they push great. This is why they are located in the tank. That way they don’t have to suck, just push. I also doubt that you could pull a vacuum in the tank since the tank is vented to the outside though the charcoal canister.
Now if you were to run the pump dry, there would be no fuel circulating through the pump to cool the electric motor. Extensive running of the pump dry could cause the pump to burn up.* Just running a car out of gas would not do this. If you were to continue to crank the engine excessively after the car died in a vain attempt to restart the car, this could cause the pump to overheat and hasten a pump failure.
*I mean burn up in th electrical sense, not as in an open flame.

Also the fuel lines form a loop, the pump pumps gas from the tank to the injectors, the gas that is not used there is returned to the tank.