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Had to get gas just before getting on the freeway this morning for my 45 mile trip to work, so I reset the mpg and decided to leave it on for the trip. 45 miles, all expressway, gently rolling (this is KY after all!). I didn't do any "hyper-miling" tricks, or drive any different than normal. Most of the trip was 70-75 mph, about half the time with cruise on, and about 3 miles of stop and go idiots. Got off the ramp to the office, and the gauge read 26.4 mpg - unbelieveable!!
 

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Sorry to burst your bubble, but the computer is optimistic. There is only one way to accurately determine fuel mileage. No doubt driving slower like that will get respectable mileage, but you may find it more in the 22-23 range. The computer is usually 10%-14% optimistic.
 

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Sorry to burst your bubble, but the computer is optimistic. There is only one way to accurately determine fuel mileage. No doubt driving slower like that will get respectable mileage, but you may find it more in the 22-23 range. The computer is usually 10%-14% optimistic.
:rolleyes:
 

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Best way to calculate your actual mileage is doing the math...miles driven divided by gallons consumed.

The avg mileage calculation shown on EVIC is a data snapshot of mileage at the time but not an overall average for the whole trip.
 

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The best I have done so far is a long trip on I-10 and mine got 25.4 with MDS. I have since disabled MDS so now about 22 is the most I have gotten using mileage & fuel calculation.
 

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I got over 30mpg in my 2012 C on the 200 mile trip home from the dealer I bought it from. You can see my overall average in my sig. Seems my car easily gets 30+ on highway section but REALLY plummets when you have to stop&go.

Also, I don't think I've ever been on a forum where they don't try to say that the (Brand X) trip computer is "optimistic" however of the 3 cars I've had with such a computer I've never calculated an actual mileage more than 1 mpg different than the trip computer, and in any of the 3 brands (Cadillac, Mazda, Chrysler) it is not consistently optimistic or pessimistic. It is my personal belief that the trip computer is more accurate and that the variance is probably related to the difference in fill level when I refill since different pumps behave differently and I sometimes top off to get to a round $ on the total price.

Since with modern fuel injection the computer should be aware exactly the fuel used as well as miles traveled it seems like this is the most accurate. However I don't understand this about the EVIC showing a "snapshot" of your average. How do they determine what the average time is? Also, if it's just some random snapshot how is it always so close to my calculated?
 

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My Mazda's computer is 12%-14% optimistic. That's calculated over four tanks of gas a couple of years ago. My Ram's computer is about the same. Neither my wife nor I can drive slow enough to get north of 20 on the C. Her best is just a tick under with four people and a fair bit of luggage and all interstate.
 

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Interesting... I do Fuelly for the 300 with every fillup and I think the only time it was off by more than 1mpg was when I had re-set it not in sync with a fillup... and it was 2mpg pessimistic in that case.

Also, where are you seeing that the average fuel economy is not the actual average fuel economy but a "snapshot"? According to the manual for my 2012

"Average Fuel Economy / ECO Fuel Saver Mode —
If Equipped
Shows the average fuel economy since the last reset.
When Average Fuel Economy is selected,"
 
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