I've seen all the fuel mileage type questions, but I have a different one. I used up my first tank of gas from the dealer on my new G35X. I know you aren't supposed to take it really low, but I decided to just this once to see what kind of mileage I would end up with. I ended up filling up with about 3 miles left till empty, or 320 miles (man I hope that improves).

However, on the fillup, I only put in 18 gallons worth. I thought I was fairly certain I had emptied the tank almost completely. Is it possible that my odometer readings could be calibrated incorrectly? Has this ever been a problem?

My "Distance to Empty" on the display went to *** at about 10 miles, and I drove about another 7. Hard to believe there was still 2 gallons left. Thanks!

The fuel pump is submerged in the fuel tank. It is lubricated and cooled by the fuel. If it were to run real low, it would not have this kind of protection. The system is designed to allow for some fuel reserve regardless of what the display shows.

It's a 20 gallon tank - so they (manufacturer) usually put in a gallon or two safe buffer for the Distance to Empty.
And for your first tank you got about 17.7 mpg - not bad for a new engine!

The X seems to have the same tank/pump as my Z did. 20 gallon tank, warning comes on about 18 gallons into the tank.

I think it is do for two reasons:

One, as a buffer

and Two, so that you do not burn it all the way down to the "swill" gas at the bottom. At the bottom of your tank all of that fuel sediment will settle. No fuel is 100% filtered, pure, absolutely clean gas. Those tiny particles will settle and get sucking into your fuel line and clog injectors, etc. That is the best reason not to burn it down to the bottom. Your probably safer doing that when you car is brand new, but the more gas you pour the more sediment there will be.

I've driven much further (100km) when the DTE says ****, It's designed to be very optimistic so that you don't get into trouble.

C.

IMO that debris in the gas is a big ol' myth.

After all the gas outlet from the tank is somewhere in the bottom - else how would you ever get to use the last 2 gallons ??
Think about it - the gas would always flow from the very bottom.

Thanks for the input. I was not sure because on my old Honda Accord, if it said 3 gallons left, that is what was really in there. As I said, I don't usually run it down that far but I was experimenting.

I guess 17.7 isn't bad. If it comes around to 20mpg in a few thousand miles I'll be perfectly content. I'm just glad I'm not the dude (forget the name) getting 13!!

Thanks again.

FWIW I drive my car pretty hard @ 300 miles a week and my mileage has gone from 18mpg originally to @ 21mpg now (4500 miles).

IMO, the "miles to empty" and the fuel gauge are approximations. How you're driving, and whether your car is level or not affects these figures. The way I've been calculating mpg is: when I fill up my tank, I press the trip button to set it to zero. Then, the next time I fill up my tank, I know how much gas I loaded (and if I'm too lazy to write it down, I keep the receipt). I also know how many miles I drove from the trip meter. So, there's no need to run the tank to empty if you calculate it this way.

Here is something to thing about. Most fuel tanks are not smooth on the bottom and if sediment was never an issue consider this. Why do most car have two fuel filters? They don't create fuel tanks that are smooth on the bottom and tilted toward a "drain at the very bottom". Fuel has sediment if that were not true why a fuel filter, or TWO? It is an issue and the fuel tank does not suck gas right out of the very bottom, the fuel pump is inside the tank and is higher than the botom of the tank. Think of a gas tank as a coffee mug which has grainy coffee in it. At the bottom are a few coffee grounds, you don't want to drink grounds and neither does you car.

FUEL FILTERS
The fuel filter is the key to a properly functioning fuel delivery system. This is more true with fuel injection than with carbureted cars. Fuel injectors are more susceptible to damage from dirt because of their close tolerances, but also fuel injected cars use electric fuel pumps. When the filter clogs, the electric fuel pump works so hard to push past the filter, that it burns itself up. Most cars use two filters. One inside the gas tank and one in a line to the fuel injectors or carburetor. Unless some severe and unusual condition occurs to cause a large amount of dirt to enter the gas tank, it is only necessary to replace the filter in the line.

The "Distance to Empty" indication is false. On my coupe I've driven it pass the point of "0 Miles left" (it actually displayed *** instead of miles ) for a couple of days before refueling. I think it was designed to give you a heads up to make sure you don't get stuck without gas. At any rate, don't rely on that reading to get an accurate view of how many miles you have left. It also varies on your driving habits.

I don't know how accurate this is anyways.
Kramer brought that Saab to 0 miles remaining while running all his errands on Jerry's test drive and then ran it some more.... for hours, and they never ran out!

I had to throw this in....

I had drive 27 miles after the fill up and this shows... it shows that we can get good MPG if we want to.