My 2014 Camry tells me what it figures my current mpg to be.

Right now it's at 24.5mpg

I hand calculated my mpg after filling up yesterday and got 29.0. It's usual for me to get a higher number than what the car tells me.

What's the deal with this car being a dirty liar?

Did you reset it back to zero after you filled up last? Not the trip odometer but also the fuel economy calculator?

In my Jeep Wrangler reset it a while back.

In my Jeep Grand Cherokee, it shows my all time fuel economy because I've never reset it.

one tank isn't enough to judge accuracy, do it over at least 5 tanks and see. My car does show almost 2 MPG better than I hand calculate, and that's over every fill up on average.

HollywoodBQ said:

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Did you reset it back to zero after you filled up last? Not the trip odometer but also the fuel economy calculator?

In my Jeep Wrangler reset it a while back.

In my Jeep Grand Cherokee, it shows my all time fuel economy because I've never reset it.

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I did reset my trip meter.

Resetting the mpg indicator is not an option from what I can tell but I would need to dig into the manual.

I've got a digital reading of my mpg that I can toggle thru as I toggle thru total miles and Trip A and B miles but it also has an analog gauge for mpg, which is a waste of a gauge. Can't reset that one.

maroon barchetta said:

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it also has an analog gauge for mpg, which is a waste of a gauge.

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I always have a laugh looking at the graduations on the analog mpg gauge in my BMW.

maroon barchetta said:

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HollywoodBQ said:

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maroon barchetta said:

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it also has an analog gauge for mpg, which is a waste of a gauge.

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I always have a laugh looking at the graduations on the analog mpg gauge in my BMW.

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As much as you laugh at having a turn signal indicator?

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It's the car that makes the driver do it - at least I'm partially convinced.

I'd be testing the roll bar if I drove like that in my Jeep.

Mine usually shows 1 MPG less than the hand calculations

Are you asking how to make the car accurate to match more closely with your hand calculations or are you asking why it doesn't match closely as it is?

BrazosDog02 said:

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Are you asking how to make the car accurate to match more closely with your hand calculations or are you asking why it doesn't match closely as it is?

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Why it doesn't match.

maroon barchetta said:

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BrazosDog02 said:

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Are you asking how to make the car accurate to match more closely with your hand calculations or are you asking why it doesn't match closely as it is?

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Why it doesn't match.

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The reason for all discrepancies (I think) is because you are using direct non variable math and the car is deriving it. You know how many miles you went exactly. You know how much fuel was burned because the gas station told you how much you put back in. Its miles you went per gallon you burned. Perfect.

The car doesn't know any of that. It knows injectors, injection pulse width, fuel pressure, how hard you mash the pedal, fuel tank percentages, and who knows what else. It's deriving the miles per gallon indirectly. It has some assumptions about how much fuel is injected per pulse width and pressure, and that may or may not be perfectly true for your particular car over its lifetime.

I think of it like trying to figure out a water depth in a well by throwing a rock in it and listening for the sound vs putting a measuring stick in it.

Carmakers would need a super high precision fuel meter that measures in milligrams to do what you do by hand. That would be costly and they don't need it since they just calculate close enough otherwise.