The “almost out of gas” light came on on my 2004 Escape last week. I did a few short trips around town before I got around to filling up.
My tank is reported to be 16 gallons. According to the gas pump, I put in exactly 16 gallons on the nose that day.
So which is off? Is my tank actually over 16 gallons or is the gas pump fudging numbers? Or had I literally used the absolute last drop of fuel in my tank the second I pulled up to the pump?
It seems almost universal that cars can run for quite a while after they report themselves to have run out of ga…(what am I saying)… petrol. Call it ‘Emergency reserves’ or whatever, the needle being at the empty mark never actually means the car is empty.
What does the owner’s manual say is the capacity? (Because Wikipedia says that it’s 16.5 gallons.)
Your tank is 16 gallons, but the pipe that runs to the outside of your car takes up volume, too.
Some useful informatin here: Why 'Filling-it-up' Takes More than 'Tank Capacity'
I checked the owner’s manual, Dewey Finn - says 16 gallons.
Interesting info, bibliophage. From reading that article it sort of seems that the auto shutoff on the pump was not working correctly, since it possibly did not shut off until I was a teensy bit above the vapor area…OR…
Santo Rugger are you suggesting that there is gas inside the fuel line even when the tank is dry? I thought about that. I’ve changed a fuel filter before and there’s all sorts of gas that comes out when you open the fuel line…
For curiosity’s sake, how much gas might be left in one’s fuel line when the tank has gone dry?
Yes there is gas inside the fuel line. TRUE STORY, I lost a gas tank, while driving and did not notice it. Three miles down the road I parked and got out. When I got back it would not start, I noticed the fuel gage now read empty, Strange thought I, so I looked in the little gas door and saw GRAVEL! I found my tank a little over 3 miles back.
Wow, you drove back to fine it? 
There’s going to be a bit of fuel in there, but when you park to pump fuel, the lines are going to be full already, assuming your car made it to the pump on its own power (so it won’t fill up when you’re actually pumping). I was talking about the pipe that runs from the gas tank to where you put the pump’s nozzle in the outside of your car.
It is common for the “E” mark on the dashboard gas gauge to be calibrated to show “empty” slightly before the tank is actually empty. So for your 16 gallon tank, the gauge may show “E” at somewhere between 15 and 15.5 gallons used.
This is so it gives the drive a bit of a warning before the tank actually goes dry. Drivers get very upset when they run out of gas somewhere out on the road. And drivers have become pretty accustomed to having a bit extra there, so they expect it, and would be very upset with a gas gauge that was exactly accurate.
On my Charger, the gas gauge on the dash is basically useless, for the reason you state. However, if I hold down the music and menu buttons on the steering wheel at the same time for eight seconds*, it will put me into a different mode on the screen that usually shows my direction and the temperature. The fuel gauge works, if I understand correctly, by putting a current through the tank, and measuring the capacitance. More fuel gives a higher capacitance. When I enter the mode I described above, it will tell me how much fuel I have to the nearest pint. It’s pretty darn accurate, I’ve gotten it down to about 3 pints.
*My car has a lot of funky things like that. For example, to completely disable the traction control, you have to turn the key to the *start *position for five seconds while the vehicle is running! To disable the seat belt chimer, you have to put the key in the accessory position, insert and remove the belt three times, move the key to the on position, insert and remove three times, then back to the *accessory *position and insert and remove three times. Don’t even get me started on how to get the vehicle computer codes to pop up!
The question isn’t about the gas gauge, though. It was about how I could need exactly 16 gallons of gas for a 16 gallon tank. I realize the gauge is not completely accurate - I just mentioned it as a bit of background in case driving around with a near-empty tank would affect the amount of gas I ended up needing.
Got some great answers, however. Thanks!
In my experience, it’s a bit more than slightly. On my 2004 Mazda 3, I had thought I had a 13 gallon tank, as when I’ve buried the needle (a little past the E), the most I’ve ever filled up the tank was just over 12 gallons. Turns out it’s a 14.5 gallon tank.
Slight hijack, sorry:
Damned near every vehicle I’ve driven, of many, many makes from 1972 models up to 21st century ones, have a fuel gauge that takes forever to go from full to half, but then the bottom half seems to fly by in a couple of days. Am I imagining this? If not, what’s up withit?
It’s not so much that the bottom half flies by (at least not in my experience), but that it takes a while to get from “over full” (beyond the “F”) to “full,” when it starts tracking fairly accurately. From my experience. when I hit the half-way point, if I continue driving the same way, I can pretty much expect to cover that many miles before hitting empty. In other words, if I hit 200 miles by 1/2, I can expect another 200 miles before being completely empty. In my car, I can go about 35-50 miles before the fuel gauge dips below the “F”.
It could also be the gas pump. Gas pumps are calibrated at a certain air temperature - gasoline expands and contracts as it changes temperature, so if the temperature was hotter or colder than the calibrated temperature the pump will read a bit off.
But then, if the pump reads off because the gas has more volume, I would expect your tank to not quite hold 16 gallons either. I guess it could if the gasoline changed temperature.
The more likely explanation, as others said, is the gas that you had in your fuel lines and in the filler neck. If you think about it - you fill a new car with gas, and it has to turn over a few times to draw fuel through the lines into the vehicle. Now you fill it up again, and you also fill it right to the filler neck. So you’ve got extra gas in the filler neck and in the fuel lines.
My friend at work, Ron, has an uncle who retired from Ford.
The old standard was that “E” on a Ford would be 2.5 gallons from dry.
Take that for what it’s worth.
Gas tank volume is calculated with a certain amount of head space for expansion at the top of the tank. If the pump does not shut off correctly it is possible to put gas into that head space. You can also put fuel into the filler neck. So it would not surprise me if you actually could put more than 16 gallons into the tank.
Oh and forget about the gas in the lines. As soon as the pump sucks air, the fuel pressure in the line drops to zero and the engine stops. There will still be fuel in the lines, but it will do you no good. Fuel injection is not like the old days where the carb would keep running.
Oh, and fuel gauge calibration? Gas gauges are a wild assed guess at best.
Another item: the type of nozzle at your gas station. Has everywhere gone to the nozzles that trap the gas vapors? You could lose a bit to evaporation (sublimation?) while filling. And of course if you spilled any overflow while filling, that doesn’t count.
IIRC my car’s filler pipe can hold > .5 gallons.
I’m guessing you had what was left in the system between the tank and the engine.
Sublimatin is when a solid that is warming skips the liquid phase and goes straight into the gas phase. This occurs when the ambient pressure is much lower than the liquid’s vaporization pressure. Gasoline (and many petroleum products) have a vapor pressure much higher than one atmosphere. I doubt there is more than 1/100 of a gallon lost to vapors during filling up.
Rick, do you think the new gauges like the type I described are WAGs, too?