calculated vs. computer MPG - Please post your results

Update:

6/14/10 / 384.5 miles / indicated 49.5 / calculated / 47.632

6/20/10 / 289.5 / 51.8 / / 49.554

6/27/10 / 346.1 / 55.1 / / 53.131

6/28/10 / 286.9 / 58.3 / / 56.823

For some reason the average for the last four tanks is under 2 MPG discrepancy. It use to run around 3 MPG.

The last tank with 286.9 miles, when my wife and ,took a trip from Seaside Oregon to Cabelas in Lacy Washington. Via Hwy 30 from Seaside to Interstate Hwy 5 to Lacy Washington.

Temps were in the low to high 60's on average. Speeds were from 55 to 70 mph with at least 40 miles, maybe more, on cruise at 71 MPH indicated, probably 70 MPH true, on Highway 5 were the legal speed limit, in some areas is 70 MPH, for passenger cars.

I was really suprised at 56.8 MPG, that was round trip so everything is equal. Also only 1.5 mpg off the computer.

Impressed, considering we were only getting in the mid to high 40's MPG(calculated) a few months ago.


alfon

 

Hello everyone,

I noticed that the calculations from the dash are clearly not the reality at the gas tank...thrilled to see others posting on the topic.

According to the dash, i'm getting 52mpg on average.
According to the math, I'm getting 43mpg on average.

Would be really happy of the 52mpg were real, rather disappointed with the 43mpg.

 

2-3 MPG, consistently across the first five tanks.

 

I recently did a drive of about 1400 miles and like others, I noted that the displayed MPG was a couple percent more than that calculated based on gasoline purchase.

What I'm thinking is that Toyota calculates fuel delivery based on injector delivery only, while ignoring the fuel vapors delivered to the engine via the closed evaporation system for the gas tank. If the tank is well ventilated so that vapors are continuously removed from the tank, then perhaps evaporation delivery is significant. This would be the case for all vehicles, but it's just more apparent when fuel consumption is so minimal.

For example, if I'm only using one gallon per hour, then each 1.28 oz. evaporated per hour would make a change of 1% in calculated mileage.

The "additional" delivery from gas tank vapors would not affect combustion since oxygen senors would compensate.

 

I am a new owner and have about 1700 miles on th car and the most I have seen is 45. Also, my battery never reaches 8 bars? Does the car gave to break in? I drive mostly in ECO mode.

 

O7/05/10
106.8 miles / 1.846 gals / 58.0 indicated / 57.854 calculated

mostly highway 35-60 MPH /
weather 75 degrees / sunny and dry
AC on about 20% of the time.

Three of us in the car plus fishing gear, cooler etc.

alfon

 

That seems waaaay off. I've put a little over 5000 miles on my car and the displayed MPG and the calculated MPG typically differ by 2 - 3 mpg.

Is the 52 vs 43 based on one tank? Lifetime of the vehicle? A one time event or consistently off by 11 mpg?

 

Over the last 21 tanks, I've gotten the following discrepancies (+ is higher than actual, - is lower than actual):

+4.3%
_____
+1.6%
+5.3%
+5.7%
+7.8%
+4.2%
+2.9%
+5.2%
______
+1.6%
+6.1%
+4.3%
+5.1%
+5.6%
+4.2%
+1.1%
+6.3%
+4.6%
+5.3%
+5.0%

You can't really average the percentages, but an eyeball says its around 5% high overall. With my year-long average of 48.24 MPG, that yields an average of something like 2.4 MPG too high.

 

first 3,500 miles on March 2010 production is Prius says 61.2 mpg, Pump says 59.5 mpg or Prius reads 1.7 mpg high. Ted

 

First fuel-up!

48.1 Calculated
48.5 Computer MPG

 

We've got 12k miles on our type 2. Flogging I95 at 70-78 consistently gets 40 mpg calculated. AC on, cruise on and using hand speed control. I don't look at the instrumented mpg stuff.

 

I just updated my spreadsheet with a bunch of gas receipts I was accumulating in the upper glove box of my Prius built June 2009 and find I have complete figures on 18 tanks full of gas. The difference between the spreadsheet calculated MPGs and the Prius calculated MPGs varies between 1.3 and 3.1 MPG per tank full. That is, the CONS value of the on board display is 104% to 109% of the actual hand calculated value. I do mostly city driving and these numbers are based on getting only 34-39 MPG in a tank full. It concerns me that my mileage is so different from what everyone else appears to be getting. I'm not an aggressive driver. I practice pulsing and coasting, etc. When I questioned the service manager about this where I bought my car, he said I should drive faster! I'm thinking I might have a lemon. I'm wondering if anyone else has experienced such low city mileage.

 

Note:

31,000 miles on our Prius.

Michelin Energy Saver Tires/ 195x65x15 with 44 psi max pressure
in all 4 tires, Costco Nitrogen.

Over 20,000 miles on tires.

Oil, 0x20 Valvoline Synthetic / 4 quarts only / so not over filled

245.9 miles / 4.716 gals / indicated 52.8 / actual 52.141

225.9 miles / 4.020 gals / indicated 58.1 / actual 56.194

both tanks filled on 07/25/10

last tank, 56.194 mpg / highway driving only, 55-70 mph with AC
on 70% of the time. outside temps / ranged from Seaside Oregon
57 degrees / to our destination, Lacy Washington, 88 degrees

alfon

 

Through 13916 miles I recorded 294.115 gallons: 47.31 mpg. Displayed MPG before fill-up was consistently in the 51-52 MPG range. Best was an actual 436 mile trip @ a displayed 59.1 at fill-up was an actual 55.7. There is clearly a display error of ~6% better than actual. That seems excessively high to me.

One wonders whether the fuel mileage software has a customizable calibration parameter.
If not, it should.

 

I agree it should.

Between what people are reporting and what Ken said about his Toyota source, is looks like there is an intentional 5% optimistic error in the system.

If you consider that there are station pump errors (usually very small), driver top off differences and plain old human error, I'm guessing that if Toyota were set it 5% more pessimistic, then most of them could be about right +/- about 1%.

 

Okay, 11,500 miles, I get only 37 computer, 35 manually checked. I have a 2010 Prius IV, I live in south Florida and use the A/C all the time. The dealer says there is nothing wrong and I have to learn how to drive a Prius. This is my 3rd Prius. I know how to drive it. Any suggestions.

 

My experience is Honda was +8% and VW was +10%.
I think Toyota is also watching other car numbers.

Are there any cars which have the calibration capability?

Ken@Japan

 

Please see following post.
http://priuschat.com/forums/gen-iii...-answer-these-questions-esp-if-youre-new.html

Ken@Japan