Inaccurate Gas Pump?

[MPGomatic]

I filled up Slambo after 195 miles of clean driving yesterday (knock wood, she's been running really well, the weather's been perfect, and the roads were clear). The fuel gauge was in the 3/4 range. I expected a meager 4.3 gallon fill (or thereabouts), based on careful instrumented driving.

The attendant (hey, it's jersey) pumped in 6.891 gallons.

This was my normal station (of late), but a different pump and grade (switching from regular to premium).

The '99 Civic HX has a 11.9 gallon tank.

Where did the extra 2.5+ gallons go?

Could the pump be that wildly miscalibrated?

Note: I usually wait until below half full to refuel, but I wanted to have a full tank from my normal station before taking a trip up north this week.

[user removed]

Best guess would be you filled before at the same pump then changed pumps and got the greater than expected fill.

If so then refill at the prior pump at the same point on the gas guage. If it stops at the amount you had expected, as it had done before, then pull over to the premium pump and see if you can get 2+ more gallons.

Your rear end was lower than the front one the earlier fills, not so at the premium pump.

Try it and see what happens.

regards
mech

[user removed]

Most states have people who drive around unannounced to gas stations and buy exactly 5 gallons of gas, in a container precisely capable of measuring 5 gallons within 99.99 percent accuracy.

If the stations pumps are off by any decent amount they close them down and they could be liable in a class action suit in some states.

regards
mech

[MPGomatic]

Originally Posted by Old Mechanic

Best guess would be you filled before at the same pump then changed pumps and got the greater than expected fill.

If so then refill at the prior pump at the same point on the gas guage. If it stops at the amount you had expected, as it had done before, then pull over to the premium pump and see if you can get 2+ more gallons.

Your rear end was lower than the front one the earlier fills, not so at the premium pump.

Try it and see what happens.

Thanks for the suggestion, Mech! I've never seen anything this extreme before.

I'll go back to the first pump on the next visit. Both are on the same side of the island. From memory, it's level, but I'll give it a good look. Perhaps the tires were off the concrete pad on one side or the other …

[MPGomatic]

Originally Posted by Old Mechanic

Most states have people who drive around unannounced to gas stations and buy exactly 5 gallons of gas, in a container precisely capable of measuring 5 gallons within 99.99 percent accuracy.

If the stations pumps are off by any decent amount they close them down and they could be liable in a class action suit in some states.

Ah, the Silver Lining! This might be the opportunity/excuse to shoot a video segment on the Bureau of Weights and Measures.

[user removed]

Gas tanks under the rear seat are not very "tall' at all. With a filler neck 3 feet long and not coming in at the very top of the tank, the level of the car is critical.

Watch your gauge and see how many miles you go to that exact same level you mentioned in you original post. If my ASSumption is correct then you should have traveled considerably further if your fill was more complete.

If that is the case, get a foot long 2x4 and drive the wheel closest to the filler neck on the board to gain some elevation on that corner of the car. Fills should be come much more consistent.

And all that advice did na cost ye a dime LOL.

regards
mech

[user removed]

The wife's Murano would auto shut off the pump, but I could easily trickle another 2.5 gallons in the tank, listening to the gurgling noise until it got to the filler neck. Never go to the top of the filler neck or you could saturate the charcoal in your vapor recovery tank. For that reason, I just fill until the pumps auto stop on slow speed and leave it at that.

Are Jersey gas pumps still attendant only?

regards
mech

[RobertISaar]

Originally Posted by MPGomatic

Note: I usually wait until below half full to refuel,

this is possibly why or at least contributing. fuel gauges are not always linear, though certain vehicles are far worse offenders than others. every GM vehicle I've been in likes to hang onto Full for nearly 4 gallons of usage, then drops fairly rapidly down towards empty, then when on empty, there can be anywhere between none and ~2.5 gallons of fuel in the tank.

it's kind of dumb, but it works well enough.

[MPGomatic]

Originally Posted by Old Mechanic

Gas tanks under the rear seat are not very "tall' at all. With a filler neck 3 feet long and not coming in at the very top of the tank, the level of the car is critical.

Watch your gauge and see how many miles you go to that exact same level you mentioned in you original post. If my ASSumption is correct then you should have traveled considerably further if your fill was more complete.

If that is the case, get a foot long 2x4 and drive the wheel closest to the filler neck on the board to gain some elevation on that corner of the car. Fills should be come much more consistent.

And all that advice did na cost ye a dime LOL.

More great stuff!

I'm looking for my highest tank MPG ever, if the amount pumped yesterday was true (allowing for an ultra-full tank) and driving conditions permit. The variables are infinite … only time averages them out …

[MPGomatic]

Originally Posted by RobertISaar

this is possibly why or at least contributing. fuel gauges are not always linear, though certain vehicles are far worse offenders than others. every GM vehicle I've been in likes to hang onto Full for nearly 4 gallons of usage, then drops fairly rapidly down towards empty, then when on empty, there can be anywhere between none and ~2.5 gallons of fuel in the tank.

it's kind of dumb, but it works well enough.

Aye, yup! Contributing, I'd buy. But the discrepancy is crazy big.

I test a different vehicle every week. Not sure if any of them are linear. It's always fun to watch the Distance to Empty numbers changed based on driving style.