Warnning: MPG gauge meter is inaccurate for all prius

I'm not arguing the case, just asking a question. Would people really complain about a median of 3.14% (as evidenced on Epiphany2000's car) on a 30 mpg car? That's less than 1 mpg. I think the only reason that it is as noticeable is that it's on a 50 mpg car. But even still, 1.57 mpg off isn't really that bad. I came from a 2001 Saturn that didn't have a gauge... so I'll take it any day of the week. Even off by a little bit.

 

Are the Gen 2's accurate? I wonder what changed?

 

I'm not sure about the difference between the Gen II and Gen III Prii, but my Gen II is off by about 3.1% (see my previous post). This seems to be on par with what I've read from other Prius owners.

I would agree that it's possible for the MFD to report the MPG accurately, but most of the time it is marginally overstated. Moreover, given the expanding/contracting nature of the bladder in the gas tank, it is virtually impossible to calculate the the MPG for an individual tank. Thus, one has to use long-term averages in order to draw any reasonable conclusion regarding MPG.

I use Torque on my phone while driving. Assuming that it reports the fuel consumption accurately, I could calculate my MPG on a per-trip basis, but I don't think it's worth the trouble. Then again, how accurate is the odometer? Thus, anyone expecting to calculate their exact MPG is living in a fantasy world.

 

When GenIII first came out, the difference seemed to catch many GenII owners, and former Honda owners, by surprise. Even Wayne Gerdes was annoyed.

While the GenII's mpg display was not perfect, it seemed that very many owners had much closer numbers with it than with the new GenIIIs.

 

Good point. I believe people tend to emphasize the MFD reported vs. manually calculated MPG because...

1. The Prius is known for its high efficiency
2. High MPG is a major selling point of the Prius, and
3. A disproportionate percentage of Prius owners (relative to the average car owner) are hypermilers, or otherwise inclined to pay much closer attention to detail

The average person just gets in their car and drives it and assumes they are getting approximately the EPA reported MPG. Meanwhile, they speed up as they approach a red light, only to apply the breaks a few seconds later. but I digress...

 

It may increase the mpg because you will have lower rolling reisistance, and also slightly larger tire height. this will not cause the MFD to read any better because it goes off the cars odometer, not a gps. I am not positive about this but I have no gps display on my level 2.

so I think you are right extra 10 psi will give you better mpg, but it will not cause the gauge to stop over estimating the mpg. to do that toyota should calibrate the gauge, buy 4% according to most people. or they could easily make a user calibration so you just calculate your mpg and enter it and after a few times the gauge will be very accurate and calibrated well.

 

Gps some freeway runs and compare. it appears to be off even with the shorter diameter oem 16" wheel spec. Makes me feel a lot more confident to "upsize" wheels as all of the "close" tire sizes are smaller than the oem 15" tire diameter. All are about dead on with the 195/50/16 which is about 1/3 of an inch shorter diameter than the 175/65/15 which equates to about 1.2% OFF. This type of thing is pretty normal, a first gen SCION xB for example was sold in the North American market with 185/60/15 yet came stock with 185/65/15 in all other markets. and it's ecu/speedo/odo were set to the 185/65 specs.

Good thing is our cars are seeing less miles on the odo than are driven AND our mpg is higher than we think because of the extra miles being traveled.

 

No big deal really... try buying a car with 32 Hwy 25 City on the sticker (SRT-4)
only to get 22 Hwy and 18 city. Keep in mind this was 2003 and gas was $1.54 for
a gallon of "Required" Premium (Turbo Timing)... After Katrina in 2003 is when gas prices exploded in the US, if you are that old you may remember seeing $5.25 a gallon for premium on the east coast right after the storm.

 

I do remember that. The Chevy dealership in my town at the time had a great deal going. Buy one 1/4 1500 Sierra and get one free for a wonderful price of $10,000. They couldn't get them off the lots.

 

Automobile manufacturer's "Three Horsemen" of Fuel (Fool?) Economy:

1) MPG numbers they submit to EPA for blessing.
2) MPG numbers their vehicle computers report.
3) MPG numbers the owners actually achieve.

 

True... but 1 is lower than what the majority are achieving on 3 for the PC. As far as 2 it's only ~3% off.

 

Agreed, it's all just a perception of magnitudes...but, perceptions are reality to those who hold them.

...and, FWIW, the manufacturers can DIRECTLY control the accuracy of #1 and #2, and IN-DIRECTLY control the accuracy of #3.

 

I wouldn't mind if my reported mileage was a bit more accurate. However, I am absolutely delighted that my PriusC and I exceed the EPA mileage estimates. I suppose I could choose to be annoyed, but I prefer to be delighted!

 

an instant guage meter would have to be inaccurate because it is such a small sample. itz close enough though for my purposes.

 

...sorta like the GI's saying: "...close enough for government work..."?

 

i agree please tell me that when your car tells you the temp out side is 108 degrees and you know its only low 90's that you don't believe that too? there are variables with electronics, its just for estimating thats not what they base their ads on, fueleconomy.gov

 

Actually the reading on at least the 2009 is off by almost -10 mpg usually. Due to our involvement in the Auto X prize we had to install an external "racing" tank in the car. It is a 5 gallon tank. Very easy to measure exact distance/consumption with this system. So for example, if the displayed mileage (which is an average by the way) indicates 45 mpg, usually the actual measured mpg is 55 to 60. This is across a diverse range of driving at altitude, sea level, mountains etc. Due to the complexity of designing, building and installing this system I doubt there are any others out there who can verify our findings.

 

By substituting an external tank, you have confused the MPG calculation since the tank float information from the original tank shows no fuel usage (in conflict with the information from the fuel injectors). The error is a percentage, not an absolute MPH amount and is a function of your tire's revs/mile. I often compare my 2004 Prius speedometer reading with the reading from my Garmin and it does indicate a somewhat higher reading on the speedometer (about 3 MPH high at 60 MPH or +5% error). This is with my Nokians WRg2 tires which have a bit lower revs/mile than the OE Goodyear tires.

JeffD

 

If you own a Prius and you don't like the mileage, by all means trade it in for a Volt
or some other all electric car. If you can't understand that setting at a stop light running the
A/C or flooring the accelerator will cause your millage to go down, you don't need a hybrid.
For those of us who love the Prius, and it's performance, we are satisfied. Trade yours in,
our kids need Prius's and if you all flood the lots with them, perhaps the used price will
go down and we can get bargains for our university bound students. Please get rid of the
piece of junk, so we can buy them. My ex son in law loved to tell us that the Prius didn't get
50 MPG, he was right, on a trip the Sacramento I got 65. He was so wise!