I've been measuring gas mileage based on calculating the amount of fuel it takes before the gas station pump auto-stops divided into the mileage since the last tank...

We've had 3 tanks so far:

1) The initial tank from the dealer
2) Lukoil filled Full Serve on the Garden State Parkway (New Jersey-Lukoil is Russian and owns Getty I believe)
3) BJ's Wholesale Warehouse (like Costco in the Northeast only I believe)

The first fill-up at Lukoil was Full Serve and they filled it until it automatically stopped. The mileage was EXACTLY the same as the dashboard reading.

The second was Self-Serve, I filled it until it automatically stopped. The measured mileage was almost 3 MPG better than the dash reading.

I just filled up the tank at Hess on Self-Serve and the pump stopped at 9.02 gallons. Then I got curious---I decided to keep on trying to max it on up...well it took about another 1.5 gallons!!! Stopped at 10.5. If I go with the 9.02 I get 44.62 MPG vs. the 41.6 MPG on the dash (3 MPG difference); If I go with the 10.5 gallon reading, then I end up with 38.3 or 3.3 MPG LESS (a swing of 6.3 MPG).

Now I plan to measure and add to the database based on the 9.02, and add the 1.5 to the next tank (I expect another 60-70 miles more on the next time before I am on 3 clicks of the gas gauge).

I am very confused and frustrtated...perhaps Honda is dead on on the dashboard reading however...makes me wonder....and be dazed and confused...

 

Tank fill issues average out in the long run. Compare your display to your calculated results after 10 or more fillups, you can't tell what is going on in the short run. Do not overfill! If you do the extra gas goes into your vapor recovery system.

 

Thanks Lakedude. I do know about the Vapor Recovery System-but the gas does get used in there so far as I understand...

I'm only going to let it go until the pump shuts off.

 

Lakedude's right, it'll work itself out over time (and enough fill-ups).

Keep in mind that different gas pumps shut off at different points (even at the same gas station). I do try to fill up mostly at the same station or two, for various reasons:
(1) Price.
(2) Convenient location.
(3) Potentially more consistency with the gas itself.
(4) Potentially more consistency with the pump initial and subsequent shut-off points. At least they're all the same brand and were probably calibrated similarly initially (for flow rate, shut-off points and gallon-measurement accuracy), and may get re-calculated similarly from time to time.
(5) I can remember (barely) where these two are!

 

Bummed over getting about 40mpg?

My old full size conversion van got 11!

From what I have read here, fuel economy will improve even more after 3000 miles.

Be patient.

This thread may be of interest to you:

https://www.greenhybrid.com/discuss/...tips.7702.html

 

I have actually found that my mpg displayed is within +/- 1.5 mpg calculated. The display is usually under the calculated.

As ppgroup stated, your mileage will improve after 3000. My average went from 44 - 46 to about 49 - 51 since I broke 4500 miles on my car. I was originally happy with getting mid-40's (my previous vehicle was a full size pickup so I was only averaging 15 mpg with the same trip). Now that my last 3 tanks have been about 49 - 51, I would be a little bummed with mid-40's, although I expect to take a hit in the winter.

As far as overfill, I do fill it up to the max as I drive about 155 miles/day (I have over 7000 miles on the car and I got it on 4/10/06) so I want to make sure I can make at least 600 miles/tank (that way I only fill up every 4 days). From my observations, I found that I can top off about 1.6 gallons after the first click. I usually do just under 1.5 gallons to avoid any spilleage. Since I started this top off method for my last 4 - 5 tanks, I have not seen any degradation of mileage, so I doubt that I am losing any fuel do to the vapor recovery system.

Just my observations....

 

That is the main reason why I always get my gas fill-up from the same gas station - And even whenever possible from the same pump.

I have noticed that the pumps of different gas stations seem to be more sensitive and trigger at different points during the fill-up process. Some trigger on the mere presence of the gas air bubbles (Gasoline foam?) as they climb up the pipe others trigger because of the actual fuel level rising in the pipe.
I was told at one point that some gasoline brands introduce their own additives to their gas and this factor is often responsible for the behavior I noticed.

So, to get around this discrepancy I simply fill at a neighboring gas station. At least I get consistent fill-ups. In the end I get very consistent and predictable milleage even on my non-hybrids.

Regards;

MS

 

Thanks folks! I'm not upset with the mileage, just the method of measure. From now on, to the auto-off and done! At 400+ miles between fill-ups, I am not complaining about my mileage, just the method!

The interesting thing with this station, it is the first one I've seen in recent times that does not have 10% ethanol added (to replace the 10% MTBE from winter) I am not sure if they still are adding 10% ethanol at other places or if they forgot to remove the stickers for summertime.

(Side Note: Hess refines their own gas, most other brands in downstate New York use a Mobil-Exxon owned refinery-I've pretty much boycotted Exxon since the Exxon Valdez, only 2 tanks of Exxon or Exxon-Mobil since then and now am boycotting BP-Amoco for their March spill in Alaska)

 

Heh. Not to dampen your spirits anymore but...most cars running OEM tires actually have an engineered MPH error of about 3% too fast. That means when your speedometer shows you have traveled 100 miles, you have actually only traveled 97 miles. And that means your real gas mileage is a tiny bit worse than what the car is calculating. Sometimes it's worse than 3% (the worst I have ever seen from the factory was about 7%). You can check to see what your real speed is if you can find a place where there is one of those radar based "your speed is" signs on the side of the highway. Just be sure to pass by the sign at a steady speed with no other cars close to you. Using the sign's speed verses what your speedometer says, you can calculate the percent error. Then the next time you replace your tires, get tires that reduce the turns per mile by the same percent of your error and your speedometer will read closer to your true speed, and therefore your true driving distance. Note that you still need to stay with low rolling resistence tires, which also help with your gas mileage. Also note that your calculated gas mileage will DROP if you match your tires more closely to your speedometer (this is because the current gas mileage estimate is too HIGH because of the error -- and this is assuming that the speedometer is reading too high...I have also seen cars from the factory where the speedometer reads lower than the actual speed).

Another variability is the accuracy of the gas pump. Despite the "weights and measures" certification most states require, the accuracy of the pump still varies quite a lot, especially between when the gas station tank is nearly full verses when it is nearly empty. And some pump equipment (not the gas brand but the actual pump equipment used at the station) will consistently under report or over report the amount of gas dispensed. For the gas station owner, they prefer equipment that over reports the amount of gas pumped, yet still passes the state accuracy requirements. You, as a consumer, would most benefit from a pump that under reports the amount. So, if you are looking for the best mileage, you should try different gas stations (try one station for a number of tanks to help smooth out variability) to see if you can identify a station where you have the advantage.

Also keep in mind that you buy gas by volume (by the gallon in the US), but you (technically) burn gas by weight. You will achieve better gas mileage if you buy gas that is cooler, because cooler gas will contain more pounds per gallon. All other things being equal, you will get better gas mileage if you consistently buy your gas in the cool morning verses in the warm evening. The difference will be slight but it is there.

Bottom line: There is a lot of variability out there and the best you can do is average your mileage over a long period of time. And if you are a fanatic about it (and who of us isn't ), consider the things above as well.

 

Well I did go by a few radars--and you assume those radar signs are calibrated (usually not) but the MPH was DEAD ON to the dash in all cases-rather surprising... (odd to look at 28 on the dash and 28 on the sign). We have 2 right near my home and another 2 right near my folks home.

I think the digitial speedometer/odometer is more accurate than the analogue ones even though they both use the same methods to measure. Perhaps the factory calibrates the digital ones (much easier to than an analogue one).