mlw911

Been slowly digesting the archives to no avail on this issue. First the way the gas tank levels read is crazy. My guage can drop a 1/4 tank in driving 10 miles. Also for the last 3 fill ups I drove the car as indicated by digital mileage readout down to what it says is 15 miles of range left yet when I filled up the car it would only take 16.5 gallons.

Does'nt that mean I should have about 2 more gallons in reserve or another 45-40 miles. Is all of this normal? I am now going old school with mileage and fillup calculation method but would like to find out if I can drive into those last 2 gallons even though it is showing 0?

Boston Driver

...which can be fouled up easily from fuel additives. The service campaign/recall replaced those sensors. I cannot recall the model years covered, but you can check the NHTSA website for more info.

ToolmanAR

Got down to 0 on the mileage left and kept going because there were no stations nearby. I figured that they wouldn't make it so that 0 really means 0 just in case you get an idiot like me pushing his luck. While I was filling it up, I looked in the manual and it is indeed true that there is a 2 gallon reserve in addition to the regular tank. I'm guessing that when the display reads 0, that means you're starting to cut into the 2 gallon reserve, hence the ability to only pump 16.5 gallons.

On the other hand, I have pumped 18 gallons into it several times without the display reading 0. I don't trust any of the computer readings except for maybe the clock, so I always reset the odometer and start to think about gas when I get close to 300 miles. My long-term average gas mileage is all over the map, maybe at 20.5 MPG last night, and only 19.4 this morning, even though the car has only been sitting there all night. If the distance to empty is at all related to these calculations, I'm not surprised that it's often way off.

Meh.

Asgor

the recent usage history of the vehicle (I think the last 10 minutes, or so - I think the user's manual does mention it). So, for instance, if you parked your car and it showed 20.5 MPG, then once you start it up on a cold morning and let it run rich for even a minute while idling it makes plenty of sense that the reading would go down drastically to 19.4 MPG, especially if you just recently refueled the tank and the current calculations are based on very few miles.

Lastly, perhaps we should look at the "miles-to-empty" calculation as a best guess under recent usage circumstances: there is no bald scientist with thick glasses hunching over a calculator hiding in the gas tank - it's all just a relatively accurate estimate tat is in many cases off by a bit.

ToolmanAR

After 4 weeks since a reset, my average MPG was up over 20.5 MPG. Last night, drove to dinner, long term average MPG was 20.5 when I got home. This morning, I started the car and it was at 19.4. All I did was get in and start driving, and even a very heavy foot and rich conditions for a few minutes should not affect 4 weeks and 1000+ miles of averaging calculations. This is the long-term, not the instant average, which, of course, is all over the place as you drive.

Like a batting average, the long-term average should be less affected by short-term spikes and dips the longer it continues to calculate averages without a reset. In the first game of the season, you can go from batting 1.000 to .250 by striking out 3 out of 4 times, but you can go a week without a hit at the end of the season and stay at .280.

The only reason I'm so interested in this is because I've been experimenting with the cruise control lately to see if I can improve my gas mileage. According to the long-term average, I've improved by more than 2 MPG just by using the cruise on my trip to work. I was looking more at the change than the overall numbers, and +2 MPG was impressive, regardless of the absolute accuracy of the numbers.

Bottom line? Don't trust the distance to empty number when you're in the desert and you just passed the sign that says <b>Next gas station, 200 miles.</b>

Asgor

it *should* fluctuate far less. Then again I suspect that driving a few miles following a very cold start should in fact take a certain "toll" - as it were.

All in all I found the overall average in my '04 to be relatively accurate - although, like you say, I wouldn't trust it completely when in dire need.

Bobby Kinstle

it said 40 miles to go, I put in 16.5 gallons, and had driven 335 miles since the last fillup