The fuel display showed about 22 miles to empty. The OSD was showing about 29 mpg on this tank, about average for the OSD for my 2007 AWD over the past several tanks. It is still fairly new, has 5677 miles.

I normally refuel a little sooner, usually about 50 miles to empty, and still have never used more than 14.06 gallons for a fillup. This tank also computed out to my worst MPG ever, even worse than when we had a week of below freezing weather.

All things considered did I just get a bad tank or does the 15.149 fillup alone mean the gas pump was not accurate? No I didn't overflow the tank at all, but I did slow the flow rate when I thought I was getting close to full.

Comments anyone?

 

I have only put slightly over 14 in once and almost 14 (13.84) once but both times I was on 0 to empty for 15-20+ miles. Not sure but I would guess the pump screwed you.
JMO
Clif

 

Every so often, you overfill the air space in the tank, and this happens. The total amount of gas you can put in the tank is a little over 17 gallons. GPSman1 and myself have posted about this many times in the last 2 years. I have ran out of gas trying to drain ethanol from my tank and found that at 0 MTE, you have around 1.3 gallons left based on my mileage and the SG reading when I ran out of gas. This is why most of the time you can only put about 13.7 gallons in your tank at 0 MTE. This gives you the total 15 gallon tank size. If the FEH/MMH is on a slope where the right front is on the down slope, you can put gas in the air space which is designed to prevent overfilling of the vapor system in the tank. It hasn't every caused me a problem because the warning system has a delay to allow you to burn off this fuel and get back to a normal vapor space.

Over alot of fill-ups, your mileage will start to average back to the normal 13.7 gallons you add at 0 MTE. If your fill up is at the normal amount next time, and you go by the amount of gas you added, divided by the miles you went, you will think you got the best tank ever! This is why I go by my Scangauge for MPG so I get the results every minute or second I want. This may cause me to add a little speed, slow down or change roads to maintain by average tank MPG.

GaryG

 

Dittos to below. I'd just like to add you can feel comfortable running to MTE 0 all the time if you are in the city and near gas. I routinely go 30 miles PAST MTE zero, and have made it 50 miles past zero a couple times. There's quite a buffer.

 

On my last fillup the MTE was 34 and I took 12.8 gal. But on the ScanGauge the MTE was 75, which makes me think the SG is a true MTE, as I would have indeed been empty going another 75 miles at 30mpg. Seems like the FEH MTE indicator is really more of a low fuel warning.

 

Don, you most likely set the SG tank size at 15 gallons like the owners manual says, and this is where mine is set also. Both the SG and the dash MTE start a countdown as soon as you reset the tank on the SG and the automatic reset on the dash MTE. It seems the SG does not make an adjustment like the dash MTE when the gas gauge starts to drop from full. The dash MTE will readjust as it compares your mileage with 0 MTE leaving ~1.3 gallons in the tank. The SG does not readjust because it has kept the data from the reset to give you an overall figure of 15 gallons to empty like you set it for. If you had 34 MTE on the dash getting 30mpg, you had a little over 1 gallon of gas left according the dash at 0 MTE. Your SG said you had 75 MTE which would give you about 2 1/2 gallons of gas left in the tank. In 34 miles, you would be at 0 MTE on the dash, but have 41 miles left on the SG. What this tells me, is at your last fill-up, you did not have a total of 15 gallons of gas in your tank. The total gas in your tank was around 14.4 gallons which included the 1.3 gallons I say you have left at the DASH 0 MTE.

The reason most people do not get a MTE like the one on my sig page here is because the dash MTE is calculating a total of only 13.7 gallons for our tanks and leave 1.3 gallons as a safety factor. Forgetting I had 30 miles on that tank when I got home and took the photo, 715 miles divided by 13.7 gallons would put me at a 52.18mpg average. My SG read over 800 MTE when I was getting this kind of milage on the dash MTE. The fact is, I personally know it took me an average of ~55mpg to get that reading.

When everyone starts comparing the SG, the nav econ screen and the dash gauges, you start to understand fill-ups at the pump much better. When you think about it, your dash MTE reading before you fill-up, will tell you if you didn't get 15 gallons in or you filled some of the tank vapor space and put over 15 gallons in with the new fill-up and gas pump reading. There is no guess work involved when you know how the systems work.

GaryG

 

Gary, I'm beginning to understand better, but still not completely clear on everything. Here's my actual data from the last fillup:

Actual:
12.797 gal from the pump to shutoff (1st click)
29.49 mpg (calculated by hand)

Dash:
377.4 miles
34 MTE
32.2 mpg

SG:
377 miles
75 MTE
30.0 mpg
12.5 GTE

Does this agree with your analysis? Why the difference in mpg from dash to SG?

Also, I'm confused about the SG "adjustment factor" that I set when I fillup so that the GTE agrees with the actual fuel quantity pumped. My adjustment factor is now a little over 15% and changed little on this last fillup. What exactly is that adjustment factor compensating for, the fuel comsumption rate being reported to the SG? Thanks.

 

The SG and built-in do not work exactly the same, so they will NEVER match.

For example, when you "engine brake" or use the "L" gear, the built-in system knows there is no fuel being used, and MPG goes to max. At the same time, the SG reads an increase in RPM, and assumes MORE fuel is being used, and MPG hits the floor.

Also, when you are in EV mode, the SG calculates this as 9999 MPG. Pretty close, but not really infinate MPG, which is reality for those few minutes. The Built-in treats EV as ZERO fuel being used, with the SG recording a trivial amount at 9999 MPG.

All in all, in "normal" conditions... they match pretty close. +/- 2 MPG is common. I do not think you should be making "adjustments" all the time. I don't make adjustments ever.

You can be confident that the gauges are within +/- 2 MPG most of the time. This is probably better than you can calculate yourself for just one tank or two, since you cannot fill the tank the same way twice. An "empty" tank can mean your next fillup might be anywhere between 12 and 17 gallons. 15 gallons is NOT the true tank size. 15 gallons is just the nominal or "typical" fill up size.

Small samples are really hard to measure with precision, and 15 gallons is a pretty small number. So any one tank calculation ( by hand ) may be 10% off.
Since my tally on GH is for nearly 35,000 miles and 905 gallons, I know what my "true" lifetime average is... to 0.001% probably!
-John

P.S. the short trips below are based on the SG since there is no way outside of a laboratory to measure actual fuel accurately enough.

 

Don, those figures are good examples to explain and typical readings from the pump, dash and SG. As I've said in the past, the dash and the nav mpg fall off at around 10 hours of driving. The SG retains your average far longer than the dash and navi average MPG. It appears your mileage was getting better at the end of the tank and since your mileage was not that good in the first half of the tank, your dash reported a better number because of dropped data. It could have been the oposite if your mileage was worst the last half of the tank. This would have caused the SG to read higher than your dash MPG. Sometimes I maintain an average throughout my tanks and the SG and the dash (in my case the navi) are within a tenth of a gallon or so.

As far as your gas pump reading, here's my opinion. You pumped 12.8 and you had 34 MTE on the dash. The SG IMO is the best method of determining your mileage for the whole tank. Lets add up what you had left in the tank now: With 34 MTE, you had 1.1 gallons to 0 MTE plus 1.3 gallons till a dry tank. So you had 2.4 gallons out of a total average fill of 15 gallon. You added 12.8 gallons at the pump, so add that to the 2.4 gallons left in the tank. This puts your tank with 15.2 gallons at reset. I estimated your SG TTE at (75 miles) 2.5 gallons to a dry tank, so that's how I knew also you set your SG tank size at 15 gallons. As far as your TTE on the SG, you had 41 miles left and the tank had 1.3 gallons at 0 MTE on the dash so I was off by saying your last fill put you with 14.4 gallons. According to that, there was 1.36 gallons left in the tank, so your last fill was only .06 gallons less than 15 gallons your average fill.

Your trip mile reading is much closer than mine with the SG and Dash. I'm always low on my SG by ~7 miles from the dash at around 500 miles. Maybe I need to adjust the SG to match my dash trip OD. I think your adjustment has to do with distance which will effect MPG, but 15% seems high, maybe not.

GaryG

 

Gary, I did two things to "calibrate" my SGII, beside setting tank size = 15 gal.

1) Calibrated speed (HOME>MORE>SETUP>SPEED) (p16 of SG manual) using a gps and with the cruise control set to 65mph. As I recall that adjustment was +1%.

2) Calibrated fuel economy reading (HOME>MORE>FILLUP>[set gallons pumped] (p18-19 of SG manual). This is where you adjust the SG for the actual quantity of fuel pumped at that fillup. For me, this number seems to have stabilized over the last two tanks to +15%, and I probably won't change it again. I don't know what is actually being calibrated here.