Accurate MPG display

Not really sure, but I think a fully-loaded Prius in the states is around $30 K.

Most folks here find some discrepancy between the calculated mpg and the displayed mpg. However, either way you're using the car's odometer to tell you the miles (or kilometers) driven. I find a discrepancy between the speedometer and the speed on my Street Pilot. I've also used the mileage markers on the highway and found a discrepancy.

An accurate mpg calculation would have to correct for error in the odometer. And some folks have suggested that the gas pumps are not entirely accurate.

I just don't worry about it. I don't bother to calculate it. I know that the Prius is the cleanest, most fuel-efficient gas-burning car on the road, except for the two-seater Insight, and that's good enough for me.

 

Top o' the day, Habu

A 'loaded' 2007 Prius Touring Edition [Package 6, Options A and P4] is $30,874 U.S. This is the combination with all the 'bells and whistles' - Leather trimmed interior, Navagation system, Front and Side Airbags, 16" wheels with Bridgestone Turanza tires, Tire Pressure Sensing System, HID headlights with Fog Lights, 6-CD, 9 Speaker JBL Sound system capable of MP3 and MP3/Wma playback, Bluetooth connectivity, Backup Camera, SmartKey system, etc. etc. If you want more detail, log on to www.Toyota.com, enter a U.S. postal code [like 75205] and access "Build and Price Your Toyota" where you can find all the combinations available in the South Central U.S.

With the incoming Prius supply getting better, some dealers are offering discounts off Manufacturer's Suggested Retail Price (MSRP). In the Northern area of Texas, you can now fine five or more Prius in dealers' inventory available for immediate delivery.

 

<div class='quotetop'>QUOTE(daniel @ Nov 22 2006, 09:45 PM) [snapback]353330[/snapback]</div>

Indeed. An 'accurate' MPG calculation requires many factors, including properly calibrated odometer, gast station fuel pumps (of which cutoffs will vary by station) and Prius fuel tank characteristics such as the bladder capacity, which is infamously known to fluctuate based on temperature and other factors. Even tire pressure & wear can eventually (marginally) affect your odometer, which in turn will affect your MPG, even if very minor. There's an awful lots of factors that come into play, and to criticize the car for being off by 1 or 2 MPG (calculated) on a tank just seems like an overreaction, IMHO.
<div class='quotetop'>QUOTE(daniel @ Nov 22 2006, 09:45 PM) [snapback]353330[/snapback]</div>

Ditto that. I track mileage for business purposes anyway; I just don't worry if a tank is a little lower or higher than expected. It's just splitting hairs.

 

<div class='quotetop'>QUOTE(Habu @ Nov 22 2006, 03:23 PM) [snapback]353168[/snapback]</div>

Correct me if I'm mistaken. I believe that the UK version of the Prius has a conventional fuel tank, not a rubber bladder. The variability of the bladder capacity based on temperature is the source of discrepancies between MFD calculated mileage and measured mileage on North American vehicles.

 

<div class='quotetop'>QUOTE(Sarge @ Nov 23 2006, 10:05 AM) [snapback]353525[/snapback]</div>

All you need to know is the real distance driven and the real amount of gas put into the car. Individual tankfuls will fluctuate around the actual mpg, but over several tankfulls you'll know your real mpg. The flakey gas bladder is not an issue unless you want an accurate measure on each tankful.

And it's the bladder that gives us the PZEV rating, by preventing evaporation of gas from the tank.

 

According to my spreadsheet - over the past 6 months the MFD and I disagree by a whopping 0.49 MPG. Or to put it another way, the MFD reads high by about 1%. I can live with that.

Now, that doesn't take into account any possibly inaccuracy in the odometer itself - something I currently have no ability to measure. However, if the Odometer were off by X percent, it would affect both the cars readings, and my calculations by the same amount, and the ratio between the two would not change at all.

What I'm getting at here.... is that the MFD's measurement of Fuel Consumed seems pretty much spot on (+/- 1%). If the odometer's off, well, then that's a different issue...

-Ken

 

Looks like the accuracy of the MPG display varies from car to car. My first Prius, a 2005, read on an average about 7% high. It's great for impressing your friends, but not very realistic. I typically got about 48 to 51 mpg but it read 51 to 55 mpg. This was calculated over 35,000 miles using weighted average display readings compared to real mpg, so it shouldn't be affected by individual tank errors.

I've had my new 07 for just 2 tanks so far as of now the error has been 0.03 MPG. Much better.

From what I understand the fuel flow is calculated based on the duty cycle of one of the fuel injectors. I guess if the fuel pressure is slightly off or the injectors aren't well matched you could end up with errors in the calculations.

 

On my 2004 Prius, in a 2-year period, the MFD MPGs read 98.5% accurate compared to hand-calculated MPGs over all the tanks of fuel. To quote an old saying: "That's close enough for government work!"

I have less than 400 miles on my new 2007, still on the initial "full" tank, so I have no readings yet.

 

<div class='quotetop'>QUOTE(kdmorse @ Nov 23 2006, 08:38 PM) [snapback]353612[/snapback]</div>

Most highways have mileage markers. Drive ten miles or so and note the ODO reading at the start and finish and you can calculate the error. (Which might change with tire inflation and wear. I don't know if that would be significant.)