Gaslog?
 

my method of computing my gas mileage is that i get $20 when my low fuel light comes on. then i keep note of how much gas and reset trip meter and when low fuel light comes on again i divide the fuel into the miles i have traveled.

example: i fuel up on 9/26 and $20 got me 7.877 gallons of gas. rigtht now trip meter is at 232 and gas gauge is just a tick below 1/4 tank. low fuel light comes on around an 1/8 or so.

based on my scanguage readings i figure another 35-50 miles before it comes on

is that acceptable or would you rather see from a full tank to say 1/4 tank then refuel and go by how much i used??

I think as long as you can accurately tell how many miles and how many gallons it took it really doesn't matter which method you use.

due to inaccuracies in gauges, I would go with a full fill up vs mileage.

Actually it really depends upon how accurate the low fuel light is and if you catch it when it actually goes on - but it should be pretty accurate as they usually indicate 1.5 or 2 gallons remaining in the tank and would not be off by Half a gallon or more like the fill until the first click method. Even my fuel gauge is pretty consistant at certain marks and a 10 mile distance of travel will move the needle so it should be pretty good. Going to empty just gives the miles from the last fillup of gas so you get the results of that brand from that pump right then and there which is a little more accurate than filling or short filling and blending from different stations at different fuel temperatures.

LxMike -

I don't use the ScanGauge for total MPG. I always reset my odometer on my car between fill-ups. I wait until I am at about 1/4 tank. Then I pay cash and get somewhere over 3/4 tank. At that time I record the amount of gas, price of gas, and the odometer reading, and reset the odometer. This means that the odometer reading is not in synch with the amount of gas I have just added. However, over *time*, the total amount of gas and miles makes the error insignificant and I have what I consider to be a very reliable measure of MPG. I only use the ScanGauge for "trip checks", aka relative performance from day to day. I don't trust it to measure my overall MPG.

Note : Odometers can be off too, especially of the tire size is not to OEM spec, so that needs to be taken into account.

CarloSW2

Why?? It can be very accurate if you use the adjustment features.

zpiloto -

I have been doing it this way since 2000, going back to my MPG figures on my previous 1997 Saturn SC2 coupe (RIP) as well. The ScanGauge doesn't fit my current way of gassing up (hate filling up to the top, like to pay ca$h), so I don't use it. Also, I have read that emptying your tank risks putting Gas tank "remnants" into the engine.

Also, the ScanGauge doesn't have tank input granularity. I have a 12.1 gallon tank. The ScanGauge only allows me to input 12.0.

CarloSW2

I just use my scanguage for current mpg and daily trip mileage figures. I'm figuring the light will come on based on the gas i started with and the daily mileage numbers i have beeen seeing. . 35mpg would be 275 miles and 37 (which i'm shooting for) would be 291 miles right now i'm at 232

Yeah I hear ya on the tank size I have a 11.9 gallon tank and they said you can enter liters and then switch back to gallons but that didn't work either - it stayed the same number as gallons.

The empty tank getting junk into the engine is an old wives tail . . . think for a second . . . the fuel pickup is at the bottom of the tank ALL THE TIME!!!! Do you think there is junk floating ON TOP OF THE GAS?? Just fill up and reset the SG each time - the only thing you loose is the measurement of gas remaining and GUESS WHAT . . . if you run the SG out of gas it stops counting anyway so set it to the next bigger tank size or smaller if you like but not smaller than the number of gallons you will burn before resetting it and check it with amount of fuel used not remaining and you will be ok with everything it measures and calculated except for remaining stuff (miles gallons time). You will still have tank average and miles driven etc.

JanGeo -

Inputting the value as liters may be ok. Go back and check to see the liters value of the Gas Tank. If it hasn't rounded up/down to the Gallons value, then it should still be computing correctly. I have a hunch that the *display* of the gallons will always be in error, however.

Ah well, me and my old wives tails. You'd think someone would complain about all the hair they leave behind during the shedding season. I will confirm what you said with my special-super-secret-car-expert friend.

CarloSW2