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They told me that I would get 60 miles per gallon. I have had this car a year, now, and have only been able to push it up to 54 once and that was on a trip. What is with the EPA estimate of 60 MPG?
 

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EPA mileage is calculated under ideal conditions and don't reflect the real world of driving. The EPA is changing the way they calculate mileage either next year or the year after, not sure. I use a rule of thumb to subtract 15% from EPA estimates to put the mileage at a more realistic number.
 

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CLAUDAIN said:
They told me that I would get 60 miles per gallon. I have had this car a year, now, and have only been able to push it up to 54 once and that was on a trip. What is with the EPA estimate of 60 MPG?
60mpg is the EPA City rating. It used very specific non-real world conditions to arrive at that number. Those conditions specifically work against most cars that idle, but work very well for Prius.

It's quite possible to get 60mpg, but it isn't easy.

The combined MPG is 55, and the Hwy. is 51. You didn't mention your driving conditions, commute type or distance, location, how you drive, etc.

I strongly urge you to completely read the following article and see if it doesn't answer all your questions:
http://priuschat.com/index.php?autocom= ... ticle&id=3
 

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Some cars do hit the EPA numbers. The Kia Sephia I traded in on my Prius was estimated at 25 city, and by golly when I wasn't on a trip somehwere I averaged 25MPG. 36MPG while driving on a highway was above the estimate, but I needed to use X-1R additive to manage that.

The way I look at it, always being over 45MPG on average beats what I had going, so I don't cry much...
 

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Discussion Starter · #5 ·
miles per gallon

I guess that I should know that if this number was going to be used to compare the performance of different cars, the conditions for testing would have to be the same for each model. Then, I am able to assume that 54 mph is pretty good. Efusco wrote that I didn't say what the conditions were. I was on the freeway and it was sunny, and cold with some wind. And I didn't stop from Portland to Seattle. And I put the cruise on at 62, not many cars so I didn't have to change. But, usually around town I manage to keep it in the middle 40's. Guess I should be happy.
 

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QUOTE: They told me that I would get...

Who were "THEY?"

Priusonline and PriusChat forums are your very best source for accurate, real world information on the Prius. The EPA published numbers represent laboratory conditions and few (if, indeed, any) cars achieve those.
 

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60 mpg

60 mpg is the EPA around town mileage with 51 mpg for highway driving. The mix should average around 55 mpg.

I had 62.4 mpg on my last tank for 585 miles. It is possible to beat all of the EPA estimates if you are willing to put any effort into it.
 

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Note that it's not Toyota's test. It's a test cycle established by the EPA, used to test all cars against it for an apples to apples comparison. If you know what your real-world fuel economy is in the car that you are/were currently driving, calculate the % difference from the EPA numbers on it, and then apply the same % difference to the Prius' numbers and then you'll have your "real world" numbers. "Real world" numbers are whatever you individually would get, depending on how you drive and where you live and how you maintain your car. The EPA even states that "Your MPG will vary." ( http://www.fueleconomy.gov/feg/why_differ.shtml )

US EPA Fuel Economy ratings for cars going back to 1985 are available at: http://www.fueleconomy.gov/

The cars are not put on a closed test course, but they are put on a stationary dynometer (rollers under the wheels) in a lab and "driven" in a specified pattern.
http://www.fueleconomy.gov/feg/how_tested.shtml

http://www.fueleconomy.gov/feg/fe_test_schedules.shtml
<quote>
City: Represents urban driving, in which a vehicle is started with the engine cold and driven in stop-and-go rush hour traffic. The driving cycle for the test includes idling, and the vehicle averages about 20 mph.

Highway: Represents a mixture of rural and Interstate highway driving with a warmed-up engine, typical of longer trips in free-flowing traffic. Average test speed is about 48 mph and includes no intermediate stops or idling.
</quote>

For some information published from Toyota on the issue:


Tips for better Prius Gas mileage (near end of Spring 2004 newsletter): http://www.toyota.com/html/hybridsynerg ... ng2004.pdf

Prius Fuel Economy: Explaining the EPA Ratings
Toyota explains what the EPA ratings actually mean, and lists ways to
improve your MPG
http://autos.groups.yahoo.com/group/toy ... sage/71431
http://autos.groups.yahoo.com/group/Pri ... ssage/2742
http://www.priusonline.com/viewtopic.php?t=1079

Prius Fuel Economy Factsheet:
http://www.toyota.com/images/vehicles/p ... conomy.pdf

Can I expect to get over 50MPG in the new Prius?
(see question #6): http://www.toyota.com/vehicles/2005/prius/faq.html
http://www.toyota.com/vehicles/2006/prius/faq.html

Other sources:
More MPG tips are in the Prius User's Guide:
http://john1701a.com/prius/prius-userguide.htm

Gas Mileage Tips from the EPA:
http://www.fueleconomy.gov/feg/drive.shtml

There are also more MPG tips in your Owner's Manual.

There is a Prius MPG calculator for the Classic Prius in the toyota-prius yahoogroup's FAQs, but I don't think anyone has recalibrated it for the 2004-? Prius yet, but it should give you some ideas where you might be losing your fuel economy:
http://groups.yahoo.com/group/toyota-prius/message/6299

In case you can't tell from the above, things like how long (or short!) your trips are, speed, tire pressures, your driving style, terrain, outside temperatures, cabin climate settings, gasoline type used, oil type and fill level, will all contribute to your final fuel economy figures.

meanwhile, on the topic of published EPA ratings, I suggest reading the following article (with plenty of citations for source data):
http://www.bluewaternetwork.org/reports ... ehood2.pdf
"FUEL ECONOMY FALSEHOODS: How government misrepresentation of fuel economy hinders efforts to reduce global warming and US dependence on foreign oil" by the Bluewater Network, 2002
 

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Here is something else to consider. The MPG the computer calculates is an estimate based on the fuel it thinks it's using. For my car, it is fairly close. I've kept a log of the following information when I fill my tank:

- ODO Reading
- Miles traveled (consumption screen)
- Gallons of Fuel
- Average MPG (consumption screen)

Taking the actual miles traveled and dividing by the total gallons of gas pumped (not including the last fillup), I've determined my MPG to be 48.5137091.

Adding up all the Average MPG entries and dividing by the number of entries, my car's computer would say my total MPG is 49.3513158

The differance is less than 1 MPG, but it's something to think about.

The other things I've been able to track are:

AVERAGE GALLONS ADDED PER FILLUP: 9.0380129
AVERAGE MILES PER TANK OF GAS: 437.857143
BEST COMPUTER CALCULATED MPG PER TANK: 54.3
WORST COMPUTER CALCULATED MPG PER TANK: 46.1
 

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CaPriusLover said:
Taking the actual miles traveled and dividing by the total gallons of gas pumped (not including the last fillup), I've determined my MPG to be 48.5137091.
Why would you exclude the last fillup? If you start the entire series with a full tank (and don't count the fillup that got the tank to full at that point), the fillup after each drive replaces the gasoline (and thus calculates the quantity of gasoline) you used to drive since the previous fillup. So you should exclude the initial fillup but include all those that follow, including the last one.

CaPriusLover said:
Adding up all the Average MPG entries and dividing by the number of entries, my car's computer would say my total MPG is 49.3513158
That's a nonsense calculation unless you used exactly the same amount of gasoline between each fillup. Here's an example to demonstrate: Imagine you've filled the tank on three consecutive visits to a service station. The first was when you bought the car. The second was after driving 400 miles, and you filled up with 10 gallons and the computer reported 40.0 mpg. The third was after an additional 200 miles, and you filled up with 4 gallons and the computer reported 50.0 mpg. It's obvious that you've driven 600 miles on 14 gallons so that your overall mpg is 42.86, and that your computer got the correct answer both times, but the simple mean of your two computer readings yields 45.0 mpg, the wrong answer. You need to weight each computer reading by the number of gallons used and divide by the total gallons to get a weighted mean:

[(40.0 * 10) + (50.0 * 4)] / 14 = 42.86
 

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CaPriusLover said:
Taking the actual miles traveled and dividing by the total gallons of gas pumped (not including the last fillup), I've determined my MPG to be 48.5137091.

Adding up all the Average MPG entries and dividing by the number of entries, my car's computer would say my total MPG is 49.3513158
I know that I've had trouble remembering the ins and outs of significant digits, but there is no way that you can have your MPG to have that many digits. Odometer is only to the nearest 0.1 mile, most gas station pumps are only to the nearest 0.001 gallon. You just can't have more digits than your least significant figure...
 

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highroute said:
Why would you exclude the last fillup? If you start the entire series with a full tank (and don't count the fillup that got the tank to full at that point), the fillup after each drive replaces the gasoline (and thus calculates the quantity of gasoline) you used to drive since the previous fillup. So you should exclude the initial fillup but include all those that follow, including the last one.
I started keeping track after 6000 miles. If I fill up my tank and record the ODO reading of 6000 and 10 gallons, my next ODO reading tells me *about* how many miles I got from the tank of gas. If on my second fillup my ODO read 6400 and 9 gallons and included the last tank of gas, I'd be saying I used 19 gallons to go 400 mile. But I didn't!! So I leave off the last tank of gas.

As for the Average the averages, it was something I pulled out of a hat to see what I got. I'll try your calculation and see what I get. It should be more accurate and will give me a clue as to how close the computer really is.

As for significant digits, I'm just reporting the numbers excel produced. To me, anything after 1 decimal place is worth looking at. I just coppied the numbers reportd.

Thanks for the positive (?) feed back! :?
 

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To be even more accurate, for each tank fill (except the first one from when it was dry/new), take the miles driven for the interval, divide by MPG displayed. That's the gallons the MFD says you used. Add them up.
Take the sum and divide into total miles driven.

To take highroute's example:

600/((400/40.0)+(200/50))=42.86

It comes out the same as HighRoute's results in this example because in his example his MFD agrees with the manual calculation.

But lets say that the MFD reads 2 MPG higher.

My calculation: 600/((400/42.0)+(200/52))=44.88
Highroute's calculation:
((42*10)+(52*4))/14=44.86

It's a small difference in this case, since the gallons are close enough for the equation, but still a different answer.
 

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mrv said:
I know that I've had trouble remembering the ins and outs of significant digits, but there is no way that you can have your MPG to have that many digits.
All those digits come from the "Age of calculators." My sliderule never had that many digits. :wink:
 

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DanMan32 said:
To be even more accurate, for each tank fill (except the first one from when it was dry/new), take the miles driven for the interval, divide by MPG displayed. That's the gallons the MFD says you used. Add them up.
Take the sum and divide into total miles driven.

To take highroute's example:

600/((400/40.0)+(200/50))=42.86

It comes out the same as HighRoute's results in this example because in his example his MFD agrees with the manual calculation.

But lets say that the MFD reads 2 MPG higher.

My calculation: 600/((400/42.0)+(200/52))=44.88
Highroute's calculation:
((42*10)+(52*4))/14=44.86

It's a small difference in this case, since the gallons are close enough for the equation, but still a different answer.
That makes sense; your are basicaly calculating the number of gallons the car thinks it has used per fillup, adding them together and then using the result (total gallons the car things you used) to divide into the number of miles you drove. That would give you what the car thinks your overall MPG is.

Then there is that significant digit thing... :wink:
 

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DanMan,

I just implemented your suggestion. On my spreadsheet, I have 77 entries on it. My orriginal calculation adding up all the MPG averages from the computer and dividing by 77 gave 49.35.

Using your suggestion, I get 49.34
Using highroute's equation, I get 49.39.

So, if we want to stick with significant digits and use rounding:

My orriginal calculation: 49.4
DanMan32 calculation: 49.3
highroute calculation: 49.4

If I don't use rounding, we all came up with the same value!

As I see it, my orriginal calculation was damn close! :D
 

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DanMan32 said:
To be even more accurate, for each tank fill (except the first one from when it was dry/new), take the miles driven for the interval, divide by MPG displayed. That's the gallons the MFD says you used. Add them up.
Take the sum and divide into total miles driven.

To take highroute's example:

600/((400/40.0)+(200/50))=42.86

It comes out the same as HighRoute's results in this example because in his example his MFD agrees with the manual calculation.

But lets say that the MFD reads 2 MPG higher.

My calculation: 600/((400/42.0)+(200/52))=44.88
Highroute's calculation:
((42*10)+(52*4))/14=44.86

It's a small difference in this case, since the gallons are close enough for the equation, but still a different answer.
This is the way I do it and earlier this week entered in all the numbers for the first 10k miles on the car.
The MFD lifetime avg. MPG = 46.0
The actual lifetime avg. MPG = 44.9
So the MFD is (on average) 2.45% optomistic. IMO that's pretty darn good.
 

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[quote="mrvI know that I've had trouble remembering the ins and outs of significant digits, but there is no way that you can have your MPG to have that many digits. Odometer is only to the nearest 0.1 mile, most gas station pumps are only to the nearest 0.001 gallon. You just can't have more digits than your least significant figure...[/quote]

mmmmm,

divide 291.3 miles by 5.755 gallons =50.616854 mpg

on my 40 year-old Sharp ELSI-MATE EL600 calculator

Just thought I'd let ya know :eek:
 

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More Trivia!

Now that I have a column that show the calculated number of gallons used between fillups, I can come up with the following pieces of information:

Actual Fuel pumped: 695.927 gal (does not include last fillup)
Calculated Fuel Consumed: 684.265 gal
Number of times more fuel was added than used*: 49
Number of times more fuel was used* than added: 28
Average number of gallons used between fills: 8.887 gals


* The amount of fuel used is the calculated number of gallons used based on the displayed average MPG from the car.

And what does all this mean? I have nothing better to be doing with my time....
 
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