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Unfortunately, it is very difficult to get great accuracy in such a measurement. But we can settle for consistency. Mine seems to be quite consistently 3% too low (about 1.4 to 1.5 mpg).... I am finding a large discrepancy between mileage as calculated by the car's trip computer, and manual calculation. It is consistently about 2 mpg higher on the trip computer.

Except you need to average over several tanks, since exactly when a pump cuts off is less consistent than the trip computer. You'll see this if one fill-up is abnormally high when compared to the trip computer, and then the next is abnormally low. Or vice versa.I've a 9th gen and sometimes I see that.

I stick to the calculated old-fashioned way, as it's nearly foolproof.

I actually track 3 values: what the pump says, what the trip computer says, and an adjusted value where I "shift" some, usually a half gallon, between two fill-ups where this happens. Here the blue line shows the truest trends, and the green one shows the truest values. The red is what I'd get if I believed the pump each time.

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- Jack

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Nope...not "mathematically"you don't....Except you need to average over several tanks, since exactly when a pump cuts off is less consistent than the trip computer.You'll see this if one fill-up is abnormally high when compared to the trip computer, and then the next is abnormally low. Or vice versa.

All I care about is when I put(approx.) 16 gallons in, what was my MPG

If I'm strictly using actual miles driven divided by actual gallons pumped..that IS the mileage...regardless of what a computer ever "says" it is.

Any theory about where that pump or another one clicks off, is unreliable data..and should never be part of the equation

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I suppose it is better for the reality to be better than the computer, but I always feel a bit shortchanged when I watch the trip computer's display. I'd FEEL better if the trip computer was more accurate, and even a bit over-optimistic.....

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However, even if you don't accept the idea that a pump cutoff might cause a different rate of gallons used vs miles, other things, such as driving in headwinds or tailwinds, lots of hills, high speed driving, stop and go driving, outside temperatures; that might all be different between different fillups, will cause significant changes in the mpg figures you get on each tankfull of gas. For that reason, I average my fuel economy both over the last tankful of gas AND, the total miles/total fuel used since I bought the car. The overall mpg is what I use to judge fuel economy, but the last tankful mpg tells me if something has suddenly gone horribly wrong with my vehicle. If there is a significant difference between the two, I ask myself, "What were the driving conditions on the last tankful?"Nope...not "mathematically"you don't....

All I care about is when I put(approx.) 16 gallons in, what was my MPGover the miles driven"...

If I'm strictly using actual miles driven divided by actual gallons pumped..that IS the mileage...regardless of what a computer ever "says" it is.

Any theory about where that pump or another one clicks off, is unreliable data..and should never be part of the equation

- Jack

JeffJo is right. There is an error introduced by the automatic shutoff of the pump. You don't know if you filled up to the exact same volume of gas as when you started your trip. This is why you do from full tank to fill tank, unfortunately you have no accurate way of knowing if the tank is rally full or not...just approximate. If the error is 1/2 gallon, that could be 4% of the tank. But if you do, let's say 10 tanks of gas, your error of 1/2 gallon stays the same since it's only the first and last time you fill up.... Which now becomes, say .04% error.Nope...not "mathematically"you don't....

All I care about is when I put(approx.) 16 gallons in, what was my MPGover the miles driven"...

If I'm strictly using actual miles driven divided by actual gallons pumped..that IS the mileage...regardless of what a computer ever "says" it is.

Any theory about where that pump or another one clicks off, is unreliable data..and should never be part of the equation

My '19 HAH mpg is consistently better at the pump than the trip mater. It's on average about 2.5 mpg better than the trip meter, and that's measured over 31k miles. I've seen it as high as 4.1 mpg over.

Also, I pump at the same 2 pumps all the time and I NEVER top off.

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It matters not if the tank is full..period.JeffJo is right. There is an error introduced by the automatic shutoff of the pump. You don't know if you filled up to the exact same volume of gas as when you started your trip. This is why you do from full tank to fill tank, unfortunately you have no accurate way of knowing if the tank is rally full or not...just approximate. If the error is 1/2 gallon, that could be 4% of the tank. But if you do, let's say 10 tanks of gas, your error of 1/2 gallon stays the same since it's only the first and last time you fill up.... Which now becomes, say .04% error.

My '19 HAH mpg is consistently better at the pump than the trip mater. It's on average about 2.5 mpg better than the trip meter, and that's measured over 31k miles. I've seen it as high as 4.1 mpg over.

Also, I pump at the same 2 pumps all the time and I NEVER top off.

That's if all you care about is actual MPG...not "miles per tank"...

Which is what the original question was:

The thread title is, and was:

Remember:

He's not looking for miles per tank he's looking for MPG...at the end of the day, that's all he really wants.

This not a EV....where your concern should be capacity of the "tank"(meaning the battery capacity)

The MPG calculation is going to be more "accurate" base on a

For example, The OP is not going to lose 2 mpg just because he did one average of a full tank and another average on a tank with two gallons left in it...that won't skew the data enough.

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Except you need to average over several tanks, since exactly when a pump cuts off is less consistent than the trip computer.

Well, I'm a mathematician and an engineer, which is why I say that mathematically, you do. Mathematically, "click-off-error" affects your calculation, but not the actual mileage you say you are looking for.Nope...not "mathematically"you don't....

The problem is that with our (you have a hybrid, right?) 12.8 gallon tank, you may:

- Fill it to 12.2 gallons, where it clicks off.
- Drive 500 miles, using exactly 10 gallons (so the tank is at 2.2).
- Fill it up again, but this time it clicks off at 12.5 gallons.

But if you use 3 tanks, driving 500 miles each time, using 10 gallons each time, and again starting at 12.2 and ending at 12.5? Your calculation, as an average, will be 1500/30.3=49.5 mpg.

Exactly. You are assuming it clicks off at the same point every time. The point of averaging is that you don't know that, and can't estimate it. But if you use, say, three tanks? The potential error in gallons will be the same, but over three times as many miles.Any theory about where that pump or another one clicks off, is unreliable data..and should never be part of the equation

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[Edit]

What matters is the fact that it isn't filled to the same point each time.It matters not if the tank is full..period.

No, it should be based onhis manual calculation should be based onactual gallons pumped,not thesize of the tank.

Number of gallons pumped is only an estimate of number of gallons used. It is off by the difference between where you stopped pumping in the intervening fillups.

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No, it should be based on, notnumber of gallon usednumber of gallons pumped ...

Actual gallons used is what's "pumped"! That's how your getting your volume.

From both the last time and what you pump

You have to trust an/or assume that that gas pump meter you use...is metering correctly.

That's really the only wild card, all things being equal.

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Only if you fill it to the exact same level each time. If there is a difference between fill levels - which is what happens when different pumps "click off" at different places - then there is an error.Actual gallons used is what's "pumped"! That's how your getting your volume.

No one has doubted that. The difference is that different pumps, or even the same pump on different days, have a different definition of what "full" means.You have to trust an/or assume that that gas pump meter you use...is metering correctly.

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Well, I just completed a hypermiling tank of gas where my goal was to take on a challenge that OG1 suggested to me when he posted he got 801 to a tank of gas. So, my goal was to see if I can get past that almost unbelievable number. Well, I did it.

OG1 posted his odometer showing 801.9 miles to a tank of gas with consumption of 64.3mpg. But his manual calculation showed he got 66.81mpg after a fillup at the pump of exactly 12 gallons.

Well, here is mine. I just completed the hypermiling challenge with my odometer reading says 810.1 miles done on a tank of gas with consumption of 66.1mpg. I filled up with 12.6 gallons. My manual calculation is 64.3mpg, which is lower than what the car says; 66.1mpg.

Here are pictures of my just completed hypermiling run...

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MPGs has been discussed ad nauseum since Ive been on this forum...everything from what the computers says to what the actual mileage is(read: the manual way...or old fashioned way...which has been done since the Model T)

And the general consensus is...,<drum roll, please>the computer has never been and will never be as accurate as the old fashioned way when computing MPG.

So why do we have it?

Because humans, in general, want to be as lazy, fat and stupid as possible...without using their actual brains!

Oh dear! it took me about a minute! Good god...

That's going to take time away from me ordering my triple decaffeinated half-caf latte with a mocha twist from Fourbucks!!

Oh the humanity!!!

You're arguing about tank size when that has zero to do with what the original question was....It's way too much work to do what I've outlined right??

TOO much time! Id rather push a button! I'd rather be brainless!...and then we wonder why it's inaccurate.

It's a reference guide. Period.

It's not accurate.

IT wasn't meant to be.

You're still not understandingOnly if you fill it to the exact same level each time. If there is a difference between fill levels - which is what happens when different pumps "click off" at different places - then there is an error.

No one has doubted that. The difference is that different pumps, or even the same pump on different days, have a different definition of what "full" means.

Always to see someone with a STEM background and science writing skills make their point in here. Chemist/biomedical engineer here.Well, I'm a mathematician and an engineer, which is why I say that mathematically, you do. Mathematically, "click-off-error" affects your calculation, but not the actual mileage you say you are looking for.

The problem is that with our (you have a hybrid, right?) 12.8 gallon tank, you may:

You actually got 50 miles per gallon, but your calculation will say 500/10.3=48.5 mpg.

- Fill it to 12.2 gallons, where it clicks off.
- Drive 500 miles, using exactly 10 gallons (so the tank is at 2.2).
- Fill it up again, but this time it clicks off at 12.5 gallons.

But if you use 3 tanks, driving 500 miles each time, using 10 gallons each time, and again starting at 12.2 and ending at 12.5? Your calculation, as an average, will be 1500/30.3=49.5 mpg.

Exactly. You are assuming it clicks off at the same point every time. The point of averaging is that you don't know that, and can't estimate it. But if you use, say, three tanks? The potential error in gallons will be the same, but over three times as many miles.

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[Edit]

What matters is the fact that it isn't filled to the same point each time.

No, it should be based on, notnumber of gallon usedornumber of gallons pumped(which I never suggested).size of the tank

Number of gallons pumped is only an estimate of number of gallons used. It is off by the difference between where you stopped pumping in the intervening fillups.

Lol, you are quite literally the one not getting it.You guys are not getting this....

I'd actually argue that the computer is more accurate. At any time the car knows exactly which injectors are firing, when they are firing, and how much fuel is passing though them each time they fire. Alternatively the car probably also knows at what speed the fuel pump is running and how much fuel is passing through it. I would imagine that measuring fuel use at the injectors or fuel pump is more accurate than the fill up method due to the reasons that JeffJo has pointed out. I'm not going to go over what he has said because I think the explanation was quite good...the computer has never been and will never be as accurate as the old fashioned way when computing MPG.

Tank size is not the point and that's not what JeffJo is saying. The point is when you fill the tankYou're arguing about tank size when that has zero to do with what the original question was....It's way too much work to do what I've outlined right??

I would take another read though his post again and try and see if you can see why you're wrong.

2017 Honda Accord, Coupe, Touring (V6, 6AT), 2017 Honda Accord Sedan, EXL V6 w/ Navi, Sensing

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