i just filled up today myself. not paying much attention to the mpgs comparison. my fillup today was 31.59 mpg, i think SG was reporting 33~ mpg. the tank was very close. i filled like 9.6, SG thought i used up 9 gallons. increased the calibration to say 9.3. now i think i can start seeing if things start matching up better. mileage on my odometer and the SG matches now too.

 

With my last fill (which was my third fill-up), SG said I used 8.9gal, I actually filled 9.1gal so I changed the SG to 9gal (I compromised since pump accuracy is a variable) which increased my fuel adjustment to 12% (from 10.9%). My SG miles were within 1.5mi of the odometer (I have a +2% speed adjustment). I'm getting close to having this thing tweaked. Oh, I also changed my Fuel Cutoff from 24 to 17 (I don't think that will have much of an effect, but I didn't want the SG to think it went to DFCO too early).

 

I filled up the tank yesterday, and the Scangauge was actually near perfect. I filled 7.596 gallons and the SG fillup expected 7.6 gallons. The fuel economy was pretty accurate too. my actual was 38.7 mpg and the SG reported 35.6mpg. I changed the cutoff when I filled up because it was higher than the car, which I was expecting to be above the actual, so I'll have to put it back where I had it. I think it was at 20.

 

Like you, my SG's estimated gallons to fill is pretty close to actual gallons filled, but my actual vs SG mpg figures are always a little off (like 1 mpg or so), but not as far off as yours (more than 3 mpg). My biggest issue now is that this dang weather, 5th coldest February in history, is no good for fuel efficiency. I'm really looking forward to some 30 degree days, maybe in March.

 

My distance calibration is spot on now. Only 1 mile off actual. Fuel was off by .2. Sg mpg reading was 30mpg. Actual was 29.6 or so. I think im there now for calibration.

 

Try to stick with the same pump until you feel like it's really nailed down.

 

Like you, I've got my distance down. I'm within 1-2 miles actual (odometer) vs. SG. My SG speed adjustment is +2%. To confirm what Charlie said, I have used the same pump every fill-up, with the car pointed in the same direction and filled it exactly the same (at this point, I add 1.5 gallons after the first nozzle auto-shutoff). As soon as my calibration is complete, I'm going to see if I can get 2 gallons in after shutoff. I am getting closer with each fill-up. However, I don't expect SG mpg to equal actual mpg every time, there are just too many variables.

 

Does it seem fair to assume that if the car calculates the range left, that you can use that to find out how much gas is left in the tank? So if the range was 100 miles with a 32 mpg trip average, then can we assume that there is 3.125 gallons left in the tank? I wonder if this would be a reasonable way to calculating how much gas is actually in the car when the gas tank gets filled up. The manual says the tank is 10.6 gallons, but I don't expect this includes the fuel in the filler line when the pump shuts off.

 

i do somewhat the same calculation you are doing. supposedly the E light will turn on when there is 1 gallon left, I've found out it can light up as early as 8.5-9 gallons of gas left. However, when my light comes on, I look at the average MPG and give me 30-34 miles left before I run out of gas. I don't want to risk being stuck on the side of the road waiting for AAA or walking to a gas station. I don't trust the miles left gauge.

 

In all my previous cars I always filled up gas by the trip odometer. I use the fuel gauge as a guide, but ultimately fill up every x miles. The last few cars it's been fill up at around 300 miles on regular blend and about 250 on winter blend.

Let's see. I had 275 for my range and and average of 34.4 mpg. So I should have had 7.994 gallons in the tank. The pump shut off at 2.853 gal. so I should have had 10.847 gallons when it shut off. Boy, now another data point to monitor for a while.

 

You can use this logic to determine approx how many gallons you have remaining, remember the "Range" miles are conservative, so using this philosophy should prevent you from running out of gas. Also, keep in mind that "Range" is a dynamic number and will change depending on how your mpg's are trending (e.g. if you are currently getting much higher mpg than your tank average, you may actually see your range increase).

 

Did my 5th fillup yesterday. It looks like I may be as close as I'm going to get with my SG calibration:
-10.615 gallons pumped, SG estimated 10.6
-Tank miles per odometer 472.3, SG tank miles 474
-MPG per dash 46.1; MPG per SG 44.8; MPG calculated 44.5

I adjusted my Speed calibration from +2% down to +1% so my SG MPG should hopefully be lower than the calculated MPG from now on. My miles will be just a little more out of sync but I'd rather have actual mpg be higher than my reading so I get a little bit of a good surprise when I fill. We'll see how close it is from here on out.