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Discussion Starter · #1 ·
I put some miles on my car, pretty much the same route every week. I started to notice some whacky drops in mpg (calculated and recorded using fuelly). I think I found the reason. I think I've got it down to one particular gas station.... they are always about 5 cents/gal cheaper.... but my mpg is characteristically lower (almost 10%) when I fill up there. I doubt I would have noticed this without fuelly. I will avoid that place going forward, 5 cents is far from 10% clobbering of my mpg.

Just figured I'd share, and ask if anyone else has uncovered volume shortages.
 

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You might want to report them to your state's weight and measures department.
 

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In our county, every pump has to have a certification sticker from the county auditor verifying its accuracy for five gallons of flow. No sticker less than a year old, time to call the
Auditor's office.
 
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I have found something similar, and I think this is actually what your seeing here. Most stations flow rates are around the same but a few stations the low setting is putting out allot more fuel. This will cause the pump to kick off early, giving you a low MPG from actual. I've had it the other way too, where it gives you more fuel than normal. On the next fillup after this occurs, the DIC is very close to pump MPG or reading low(from a more consistent pump at a different station).

Strangely of all the brands I have tried BP is the best running fuel in my cruze, however their stations around here have the most inconsistent pumps between them. Also when I had a scanguage you need to calibrate it at fill up. Once you get it dialed in though calibrating it over and over will just give you a 0.4+/- gallon variant per fill up. I'm guessing this difference is more than likely due to when different pumps kick off.

All pumps are checked by the state here occasionally, heard they only check city's over 5,000 population annually.
 

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Discussion Starter · #6 ·
I have found something similar, and I think this is actually what your seeing here. Most stations flow rates are around the same but a few stations the low setting is putting out allot more fuel. This will cause the pump to kick off early, giving you a low MPG from actual. I've had it the other way too, where it gives you more fuel than normal. On the next fillup after this occurs, the DIC is very close to pump MPG or reading low(from a more consistent pump at a different station).
Yeah.... but I don't stop at the click off... I stop when I see fuel pooling up in the tube, I think I'm consistent with that... But I guess I could try that station again, to make sure. I"m usually pumping close to 10 gals, so I don't think there is enough variation potential in the volume of the fuel tube to affect my mpg by 10%.

I don't see much difference in mpg across brands, nor do I see much across octane ratings. But I've been running 89 rather than 87 because the low rpm driveability is markedly better.

SW PA terrain is rough on your mpg. If you're not going uphill, you are going downhill. While I have only been averaging about 35, I'm pretty happy with my overall mpg given the terrain here.
 

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IIRC, the OM states that you should stop filling when the pump clicks off to avoid overfilling the system and possibly damaging the vapor recovery system. It's not unique to the Cruze as the OM for my car states this also as does the OM for the 12 year old P5 we have.
 
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IIRC, the OM states that you should stop filling when the pump clicks off to avoid overfilling the system and possibly damaging the vapor recovery system. It's not unique to the Cruze as the OM for my car states this also as does the OM for the 12 year old P5 we have.
While true, by doing this the OP has been getting "consistent" fills.

To the OP, did this start when the temperatures started dropping. Cold weather drops my ECO MT's fuel economy by 15 to 20%.
 

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While true, by doing this the OP has been getting "consistent" fills.

To the OP, did this start when the temperatures started dropping. Cold weather drops my ECO MT's fuel economy by 15 to 20%.
Two thoughts on this.
1. How accurate is the low flow, start/stop pump delivery when you reach the shut off point and then "squeeze" that last amount into the tank and filler neck? Also, how accurate is the car computer if the tank is overfilled beyond what the tank sensor can read?

2. What is the thermal expansion/contraction of gasoline when being pumped from the constant temperature of the underground tank and then being placed in the uninsulated gas tank of the car? In warm weather, you risk overfilling the system if you fill to the top of the filler neck.

I think both of these would be sufficient to alter the mileage calculations for each fillup. I came to the conclusion a long time ago that it's better to rely on long term averages and let each tank fill up just factor into that. Fortunately, I found that the computer in my car is accurate enough to give me individual tank mileage so I don't have to mess with tank by tank calculations. Also, since the system also tells me the last four averages for the trip odometer, I can spot short term trends easily.
 

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Discussion Starter · #10 ·
Data shows no pattern with regards to temperature. No pattern with regards to brand of fuel used prior to that particular station fuel. If I'm that bad at filing consistently, the one station wouldn't show up with such prominence. I guess I should turn them in....
 

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And change station.
 

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Yeah.... but I don't stop at the click off... I stop when I see fuel pooling up in the tube, I think I'm consistent with that... But I guess I could try that station again, to make sure. I"m usually pumping close to 10 gals, so I don't think there is enough variation potential in the volume of the fuel tube to affect my mpg by 10%.
Filling that way is much less accurate than just letting the pump kick off on its own, you end up being part of the variable as well then(besides possibly damaging the EVAP system).
 
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