calculated vs. computer MPG - Please post your results

Interesting to see that 6% is the world average for the overestimation of fuel consumption....at least it is consistent....

 

I would have to agree with the majority here that MFD and calculated MPG is very different. I am finding that the MFD shows about 3 MPG higher than the calculated. Note, I only have about 3200 miles so far though.

What I find more iritating the variance in the speedometer. Actual speeds vary by 5 miles an hour versus actual using GPS. Seems to be greater variance under crusie control. On normal highway driving i am seeing a consistant 2 miles an hour slower on the speedometer vs GPS. In other words to achieve 65 miles an hour, I have to drive 67 miles an hour. The biggest varaince is under cruise, Often the speed difference can vary by 4 to 5 miles an hour, in otherwords, the speedometer does not always show the change in speed, when driving up or down hills or slight inclines. Just Wierd, never have this problem in my other cars (Chrysler Crossfire / BMW 740)

 

2010 Prius Gen III bought April 2010. My actual mileage and computer readout are close, both are terrible. I consistently get ~ 50 on the highway, but in town is about 32-33. I have taken my car back 4 times to the dealer. They gave me advice which I followed the first 3 times, and was ttold they had adjusted the valve settings. Last time they told me they had called a Toyota engineer and he said my mileage was not unusual, and there was nothing wrong with my car. I called the Toyota consumer satisfaction number and a very nice agent said there was nothing he could do if the dealer said my car was mechanically ok and working correctly. The only recourse he mentioned was to undertake arbitration. This is my first toyota, and it will be my last at this point. The mileage I get is no better than what I got in my 99 Mazda Protege. Has anyone ever undertaken arbitration, and if so, how did it turn out. Thanks for letting me ventilate!

 

With the data you collected, if you traveled a distance of 65 miles (based on MDF) in reality you actually traveled 67 Miles right? So the MPG is actually correct?

 

Perhaps you should go back to the mazda, it is a great car.

 

If you get 50 on the hwy and 33 in town, there is actually nothing wrong with the car - otherwise you would not get 50 on the hwy. Did you get that with your Mazda?
33 in town is pretty bad for a Prius, but good compared with other cars out there with similar size/weight/power, Diesels included.
This might help - try it for a while and see how it works.

 

Hi all,

I've calculated the difference between indiciated (HSI) tank averages, and the actual, pen-on-paper consumption. Due to my ineptitude with forum coding, I'm unable to work out a way to enter this data as a table that I can share with you. However, the data is available by clicking on the mileage icon in my signature below.

The summary of the last 10 tanks, at any rate, is that my car reads around 11.5% optimistic - this seems awfully high compared to what others are reporting. For example, a tank which the HSI indicates should have been 4.5 L/100 km (52 MPG), is actually 5.0 L/100 km (47 MPG).

I find it disheartening to pull into a gas station with a satisfying 4.3 L/100 km (55 MPG) tank average indicated on the HSI... only to calculate that it's actually a very thirsty 4.9 (48 MPG). I hope Toyota hears our concerns, and offers a software patch to rectify this discrepancy - or at least bring that offset value down closer to actuality.

-Iain

 

Along with everyone else my display is optimistic by about 5-6%.

Avg. display over the 10 fill-ups is 52.8.

Lifetime calc is in my sig.

Manufacture July 2010.
55mile RT commute, sea level to 1800' to 75'
Tires at 37/35
No mods.

Cheers.

 

Perhaps your state's lemon law can come to your rescue here? Have you checked that you aren't driving in "B" gear setting? Too restrictive an air filter? If nothing works then perhaps I would trade it in for a 2011.

 

Another thing I would do is to actually have the car driven for a week or tank by someone you know that also drives a Prius (preferably a G3) to see how it compares to his/her car. If it compares favorably then perhaps it has to do with the way you drive and/or the specific routes/terrrain you drive on.

 

Also, I just saw this excellent questionnare/check list:
http://priuschat.com/forums/gen-iii...-answer-these-questions-esp-if-youre-new.html

 

That sounds pretty normal to me. When I go to San Francisco, there are so many stop signs and slopes in the residential area that my city mileage is probably also around the 30's (I just see it creeping downward all day). But most of my driving is on the high way, so overall, I get 40's. It's highly unlikely that there is anything unusual with your car. The numbers you are getting is probably due to the design of your route.

Now does that translate into whether you should be satisfied with the car? That's up to you. Obviously your expectations were set higher than what you experienced, and it always sucks to get excited about something and then let down.

A lot of new/non-hybrid drivers don't realize that the MPG's for hybrids is greatly dependent on so many factors, such as the specific route, weather/road conditions, traffic, personal driving style, temperature, tire pressure, etc... the list goes on.

Also, as another person pointed out, the 33mpg you got with the mazda is probably either combined city/hwy, or mainly hwy. What overall MPG do you get with the Prius?

 

Mine is 11.5% optimistic, calculated over my last 10 tanks of fuel.

Is that the highest/worst "off" reported thus far?

-Iain

 

Iain - maybe a silly question - is the average calculated based on tanks on the same gas station/company? or did you fuel up at different places.
And just to be sure and to understand: did you fuel up always in the same way? do you top-up?

You 11.5% is quite off the chart, IMHO.

 

Because I averaged it over 10 tanks, it shouldn't matter... but I do always fill up exactly the same way. I wait for click-off, then apply one more half-pressure pull on the handle until that clicks off, then terminate the fueling. I typically use the same station, however there may be one or two other entries in that lot of 10 I used to calculate. I use spritmonitor.de to track my fuel consumption (like you) - so you can see my entries for the car's HSI vs. my calculated averages.

For example, today's fill up read 4.1 L/100 km on the HSI, but was actually 4.52, which meant a 10% error.

-Iain

 

My error range is from 3% up to 12%. OK it's impossible to refuel to exact same level. I just finished my winter cycle (changed from winter to summer tires) and I've got 8% error on distance 4898 km (I can say that refueling error can be neglected in this case).

 

Mmmmh - sounds all OK - you are fuelling the same way I do. With the only difference that I practically never fuel up in the same place - I search for the cheapest place each day I need to fuel up.
If your computer calculates correctly, or as most say including me, with 6-6,5% error, then it looks like where you fuel up they are giving you 4% less fuel. If the computer is really 10% off, then by changing gas station, you should always be around 10%.
Please note that my average is calculated over 42 fuel ups, my min was 2,23%, my max 10,66%, with 17" and 16" (winter) tires.
Try to fuel up for a while at a different gas station and see what the average looks like. If it is still around 10%, then your computer seems more off than anybody else.

I have looked at your spritmonitor profile - question: why did you have an oil change at 7500km? the first one should be at 15.000km.

 

To be 100% true on your mpg's
calculated vs computer generated
this is what is required:

Fill up at the gas station, stop pumping
gas when its is to the top of the neck
and completely full so you can not
get another drop of gas in the tank
or it would spill out.

Drive off and after a few hundred miles
fill up exactly the same way.

Now divide the amount of gallons of gas
into the miles driven.

The figure you receive will be your
true MPG's.

I know some of you will say, you can't do
that it will hurt your fuel system..

I filled up several times that way
and my car is still running fine after 46,000
miles and no check engine light went on
or anything that would have me concerned.

Also, when the pump first clicks off you can pump
in at least another 2 gallons of gas before it is
completely topped off... Thats another
90 to 100 extra miles.

al

 

The only "official" statement (I am aware of ) on computer MPG inaccuracy in these vehicles is from the principal investigator for the DOE.

quote: Jim Francfort, principal investigator at the Idaho National Laboratory in Idaho Falls, which is operated for the Department of Energy.
...
Francfort and his team also determined that the computer dashboard readings for fuel economy—which most drivers use to base their judgment rather than manually calculating the actual mpg—inflates mileage numbers by somewhere between 10 to 20 percent.
Air Conditioning and Hybrid Mileage | Hybrid Cars

 

I don't think consistant behaviour at the gas pump matters in calculating mileage matters much, and diminishing so as the tankfuls accumulate. Any error will balance out with multiple tanks.

My dash vs calculated error has averaged 7.9% since start of year.