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Actual Toyota Prius mileage doesn’t equal the readout

I’ve had 3 Toyota Prius’s. I’ve calculated the mpg on each of them and all are 6-7 % less than what the meter in the car says. I’ve calculated on different pumps and stations and always the same.

That’s about as accurate as a dash readout will be.

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Rant? Or question?

Apparently you keep making the same buying decision and getting exactly the same result. Are you surprised at that result?

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I think it is fair to say that this is something that will vary from one make/model/manufacturer to another. On my car, the disparity is less than 2%.

If it’s consistently off (like my Hyundai Tucson is 7% high) then you just make a correction.
Problem solved.

I never really concerned myself with the accuracy of the mpg read out. I reset the trip odometer when I fill the tank. The next time I fill the tank, I note the mileage recorded on the trip odometer and the number of gallons I put in the tank. I round each number up or down so I can do the division in my head. The mpg readout and I are usually close. I have never felt an overwhelming need to calculate my gasoline mileage to the millionth of a gallon.


This only seems like a problem if you run your gasoline to near empty. Even then, it tells you that you have a certain number of miles to zero al least my car does (not a Prius). If you are just puzzled by the difference, don’t be even industrial instruments are often performing well if they have an accuracy of around 5%.

Miles per gallon and miles to empty are two different displays.

Estimated MPG on the dash readout doesn’t need to be accurate, just consistent. And it appears that over 3 different cars you have found them all to be within 1% of each other. Sounds pretty consistent to me.

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I literally haven’t looked at the mpg display in my Corolla in years. I can toggle the display to show mpg, outside temperature, elapsed time, or clock. Of those, the only one I find useful is clock so that’s where the display stays. I calculate my mpg the old fashioned way whenever I get gas

Yes, but on most cars it’s pretty easy to “toggle” from one to the other.
I normally keep mine on “avg mpg”, but if I’m on a long trip I sometimes toggle over to “miles to empty” just to give me a general idea of how soon I need to fill up.

So now you know, just subtract 7% from the cars readout.

How did we ever make it in the old days when we didn’t have a readout for the average mpg, the instantaneous mpg, the distance to empty, etc.
I would gladly swap.these readouts for an oil pressure gauge and an ammeter.


The only reason I look and the average mpgs is to check on the health of the engine. If I get a lower number than I’ve seen in the past, maybe it is time to replace the thermostat.

Distance to empty is more useful.

And none of this stuff is as accurate as scientific equipment because it doesn’t have to be.

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That’s true but the miles to empty number is being derived from the erroneous mpg number.

The “error” is well within normal tolerance and appears consistent. I have always taken time to get accustomed to any new to me car nuances like this.

Checking your car’s MPG is essentially a quick–albeit superficial–diagnostic.
I like to check the average MPG readout, but it tends to be boring because my driving habits and patterns vary so little that the readout rarely shows much of a change. But, if I do see a drastic drop in MPGs (and if I wasn’t stuck in stop & go traffic for a very long time), I know that it is time to assess whether the engine needs attention.

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