calculated vs. computer MPG - Please post your results

It's not just Toyota - all car manufacturers are, more or less, optimistic/not precise. It also has to do with how expensive it is to make it perfectly accurate or even 1-2% accurate. For most people/buyers out there it would not mean much - too bad for Toyota that most Prius drivers are *actually* calculating the fuel consumption per hand, keeping track of everything and finding out pretty quickly how much it is approximate...

 

How Vehicles Are Tested
Measuring Fuel Use
"For vehicles using carbon-based fuels (e.g., gasoline, diesel, natural gas, etc.), a hose is connected to the tailpipe to collect the engine exhaust during the tests.
The carbon in the exhaust is measured to calculate the amount of fuel burned during the test. This is more accurate than using a fuel gauge."

Ken@Japan

 

Honda Civic Hybrid, second gen, in my experience and a lot of other forum poster: was consistantly pessimistic in it's predictions of mileage, by a small margin. As an example: if the dash said 5.0 liter/100km, calculated usually came in at 4.8~4.9.

I can appreciate slight inaccuracy will happen, but 6-10% error, always to Toyota's benefit, kinda smells.

 

Yes - but do we know how precise are BMWs, VWs, GMs, etc.? I don't - any resource on the web for this?
I don't expect any of the above mentioned to be "saints" either.

Too bad I have never calculated the error of my VW Polo before trading it in - that would have been interesting....

 

Here is my first comparison based on a small sample.

Date Gallons Miles Actual MPG Comp MPG Pct Diff
20-Apr 3.278 148.8 45.39 46.9 3.21%

 

Sorry if I am going back to an earlier discussion or post, but isn't there a bladder in the Prius III tank that will throw off my manual calculation of gas mileage?
I asked a dealer tech about the differences and he told me to trust the car's computer. He told me the Prius III is the closest thing to the Space Shuttle on four wheels. He has been to training sessions on the car and said it's a work of art. This guy is a Volkswagen convert from the 1960's days of VW buses and Beetles, so I trust him! :rockon:
Fred

 

Renault Scienic 2004, 1,9dci: 1% - 2 %

 

So you say the display MPG is correct. I am always 2-3mpg lower when I calculate myself. My AVG s 48 MPG on my first 3700 miles of mostly highway. Any tips on highway milleage?

 

my Prius was made in 2/2008. I have nearly 97,000 miles on my car, and have calculated mileage with every tank, and I have a notebook full to prove it. It gets, in the summer, no A/C every used, no headlites, and no heat, 49.7 mpg. I have tried very hard to get to 50. during the winter with studded snow tires it drops to 41.3 mpg. also the heat, headlights, radio are on. I am wondering if the 2010 pries gets better mpg than earlier versions? I am the only driver of this car. The computer read-out is always within one mile per gallon, and has been very accurate. Not all cars can be the same, but my prius has been a prince.

 

NO. The 2nd Gen Prius had this, but not the third. My car is typically giving a +5% FCD display to the actual mileage. Very disappointing. The car almost does as well as my 2nd Gen , by the FCD, but factoring in that 5% error, and its not even close....

 

I filled up at a BP gas station once 13 Gal But my gas tank takes only 11 Gal, so you cannot trust the gas station much.

 

No, no bladder. And, any disparity in fill technique may throw off the calc for one tank, but calc 2-3 or more tanks, and any variations will average out. If you're able to track the total miles you've travelled and the total gas you've put in, you can make an accurate calc. One calc might be high, the next low, but the overall will be right.

Really... Would you be interested in buying a bridge?

 

Prius III built Dec 2010 purchased 13 March. Currently have 2000+ miles and very concious on fuel economy! I am seeing about 3mpg difference between what the onboard computer says and what the actual fill up is. Onboard computer reads high! Currently getting about 57 mpg highway here on dairly flat roads in central Florida. Great car to pass the gas stations! I commute 65 miles each day to work. Stan in Central Florida :rockon:

 

Miles Actual MPG Comp MDG Pct Diff
148.8 45.39 46.9 3.21%
381.7 48.30 49.9 3.20%

 

Remember, when you fill up and the pump clicks off
you can still get in another 2 gallons until it fills up
to the top of the tank neck.

I am sure that the tank capacity is probably a little over
13 gallons from bone dry to full top of neck capacity.

al

 

Below is my data on my first 8 tanks. Note the MFD (MultiFunction Display) error v.s. calculated miles per gallon. 2011 Option 3. So far my mileage is about 3-4 MPG less than my 2005.

Date Miles Gal Cost MFD Miles MPG Miles Ave Days Miles MFD
MPG Driven Day Miles Tank Tank Error
21-Mar-11 280 9.164 $35.00 38.0 275 30.0 55.0 55.0 5 days 275 26.63%
23-Mar-11 555 5.345 $21.00 48.0 275 51.4 137 78.6 2 days 275 -6.71%
27-Mar-11 999 10.260 $40.00 44.5 444 43.3 111 90.4 4 days 331 2.83%
5-Apr-11 1440 11.124 $43.93 45.1 441 39.6 49 71.8 9 days 359 13.76%
8-Apr-11 1889 8.042 $32.00 51.7 449 55.8 149 81.9 3 days 377 -7.40%
13-Apr-11 2316 8.753 $35.00 49.6 427 48.8 85 82.5 5 days 385 1.67%
19-Apr-11 2563 5.419 $22.00 44.3 247 45.6 41 75.2 6 days 365 -2.81%
26-Apr-11 2987 10.077 $41.00 47.9 424 42.1 61 72.7 7 days 373 13.84%

 

I have noticed (only once though - need to test this further), that if I don't top off, I get about 3-4% error, instead of 6% when I top-off. Maybe the MFD is "accurate" when one does not top off...?

 

I've noticed that as my mileage improves, the disparity seems to increase as well.

My tanks have shown mileages of 0.978, 0.951, 0.942, 0.952, 0.940, 0.945, 0.933. My mileage has increased from 50 to 60. Others have said the differential decreases with better mileage.


I'm going to start shopping around and see if the station makes a difference.

 

Over 18 tanks, the average error was 2.8 mpg or 4.8%. The trip mpg was always higher than the calculated mpg. Date of manufacture was 7/10.

 

I have 2000 miles on my 2011. Over 4 tanks the computer is reading 5% higher than calculated. This seems in line with everyone else. A little disappointing but I would expect them to err on the high side and 5% isn't that far off.

It reminds me of the programmable thermostats I bought years ago. Of course on the package they claim big energy savings. One of the reasons? The thermometer reads 2 degrees F warmer than it actually is in the room. So if you set the thermostat to the same temp that your old one was set to, you'll be keeping your house 2 degrees cooler! Not a bad thing to get people to save some energy, but a bit dishonest.