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Discussion Starter #1
It's been 3 months since I bought my SE. I still love this car.

I've noticed that the dashboard calculation of MPG since fill-up is almost 2 mpg more than when I manually calculate mpg on my gas receipts. I fill up every time, and I go do different gas stations.

The computer calculates 24-25 averages, but my receipts are telling me 22-23.

Anyone else have this issue? I am saving my receipts and will be going in to the dealer in the next few weeks. I've had only one other issue, but did not want to spend time going to the dealer for small things multiple times. (FYI the other is that the driver head rest does not lock all the way down, but on the first click up & it moves up on me since I am a shorty who likes it all the way down)
 
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The MPG difference sounds pretty normal to me, my 2015 Limited was the same way most of the time, the display was seldom right on, usually a bit optimistic, same for my 2016 Hybrid so far, first tank calculated actual was 33.9, display said 36+. Can't help with the headrest issue, sounds like there is no detent position at the bottom of travel, perhaps someone else or the dealer will offer a solution.
 

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I've noticed that the dashboard calculation of MPG since fill-up is almost 2 mpg more than when I manually calculate mpg on my gas receipts.
That's closer than mine is. Don't worry about it. To make it perfect would require some NASA engineers designing the computer measure, and also filling your tank.

We are waiting now for you to discover all four of your tires are properly inflated but the Tire Pressure monitor light comes on. Gawd, can't Toyota design better customers?
 

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I think it has to do with the speedometer being off. Use your phone GPS app and compare your actual speed to the speedometer reading and you will see its off.
 

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My 2015 Limited AWD is the same, sounds normal to me. My average below works out to 22.7 mpg, same as yours.
 

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Discussion Starter #6
That's closer than mine is. Don't worry about it. To make it perfect would require some NASA engineers designing the computer measure, and also filling your tank.

We are waiting now for you to discover all four of your tires are properly inflated but the Tire Pressure monitor light comes on. Gawd, can't Toyota design better customers?
Well, I can tell you the tire pressure monitor is highly subjective to temperatures. Been there, done that for years. No need for the snark.

I'd be okay with some NASA engineers filling my tank though.

Otherwise, thanks for the input.
 
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I think it has to do with the speedometer being off. Use your phone GPS app and compare your actual speed to the speedometer reading and you will see its off.
Great idea. I will try this. Thank you.
 

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Computer in the car is never 100% accurate. In my last car (Lexus CT200h), the car always said I was getting around .2 - .3 l/100km better than the calculated mileage. My new RAV4 is also reporting better mileage than the calculated.
 

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I've spent a good portion of my engineering career working with combustion engine controls (mostly emissions) on stationary commercial engines. These are sometimes called prime movers, and in my case pump natural gas through interstate pipe lines. What I can tell you is that the reason there is such variability in mileage calculated on the ECU is that automobiles have no actual fuel flow meter, so the amount of fuel used is not measured with tremendous accuracy. What modern fuel injected engines do map and measure is the time that the injectors are open and they then multiply by the regulated fuel pressure spec to estimate fuel use. There is a lot of variability in this in that fuel pressure has many variations and irregularities in real life that are not factored in. What automobile fuel injection is superb at is measuring down stream exhaust chemistry and making incredibly accurate adjustments when more or less fuel is required. The volume of fuel used is simply a loose side calculation that varies with fuel feed dynamics, temperature (gasoline density varies hugely with temp)and a list of other factors. It wouldn't quite take NASA technology to make it accurate, but it would take an accurate, temperature compensated, fuel meter (which autos don't have) and an accurate odometer, which it generally does have within a few percent, and your GPS could correct if needed. Actually, in my opinion, with all the variables involved, its amazing they are as close as they are these days.
 

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Why does it always seem like the computer is showing a higher mpg average?

I don't think I've ever seen a report of it showing lower than what a driver has manually calculated.
 

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Lots of variables in that equation but the most likelywould be that when manufacturer

Why does it always seem like the computer is showing a higher mpg average?

I don't think I've ever seen a report of it showing lower than what a driver has manually calculated.
Lots of variables in that equation but a major contributor is likely that when manufacturers build vehicles to the federal requirements, the spec for speedometer calibration is written such that they are allowed to be several percent fast (optimistic) but 0% slow. They have to write a pretty complex algorithm to translate fuel injection cycle time to into fuel flow (volume/minute), and compensate with a lot of real world corrections. If you were them, and it cant be perfect, would you write it so that errors tend to be optimistic or pessimistic?
 

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If you were them, and it cant be perfect, would you write it so that errors tend to be optimistic or pessimistic?
If I were them, I'd have worked toward getting it more accurate a long time ago. The computers being "optimistic" analogy isn't a new problem. It's been optimistically inaccurate for years. I just find it hard to believe they can't nail this a bit closer. However, I'm no expert.

Then again, if I were them, I'd probably be perfectly fine with my customers thinking they're getting better mpg than they actually are.
 

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I think it has to do with the speedometer being off. Use your phone GPS app and compare your actual speed to the speedometer reading and you will see its off.

Be careful about using GPS for speed readings though as your Police might be like our New Zealand Police who refuse to accept them.They say that they have not been calibrated so their accuracy is in doubt.
 

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Filled up today - Fuelly calculated 7.9 l/100km, but the in-car display since last fill-up read 7.3
 

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Even we 4.3 owners have noted the same discrepancies between the dash computer figure, and actual mileage as determined by actual distance driven since the last tank fillup divided by the amount of fuel actually required to fill the tank.
 

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Discussion Starter #17
Filled up yesterday and for once the manual calculation and the computer calculation matched. Both said 25.2, but I am suspicious as I went to a different gas station to fill.

I don't know... if the pumps were off and giving me less than what it said, the mileage would be worse. How often does a gas pump give you more than it registers?

Not that I am complaining about 25 mpg... I'll take it.
 

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Filled up yesterday and for once the manual calculation and the computer calculation matched. Both said 25.2, but I am suspicious as I went to a different gas station to fill.

I don't know... if the pumps were off and giving me less than what it said, the mileage would be worse. How often does a gas pump give you more than it registers?

Not that I am complaining about 25 mpg... I'll take it.
There can be a considerable difference in pumps in terms of when they shut off. For accurate comparisons you should stay with using the same station and pump whenever possible. But its not so much whether the pump is measuring correctly, its a question of how much the pump will allow you to put in.

Variations in pumps will even out over 10 tanks or so, so you should rely only on averages measured over several tanks.
 

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My RAV, my Elantra and my Sonata that I traded in on the RAV all had readings that were about 2mpg below the computer readout. My speedometer is also off by about 2mph. I think I could go with a larger tire and solve the mph problem and it should help the mpg issue.
 

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In all honesty the dashboard reading is just an estimate, or a suggestion. If you want to know your MPG's then do it the old fashioned way. Common sense prevails.
 
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