calculated vs. computer MPG - Please post your results

Got that one wrong. Took 6.916 gallons, 45.4 mpg.

 

My 2010 Prius IV has over 23,000 miles and is almost two years old. The on board computer says that I am getting between 49 and 52 mpg. My iPhone Gas Cubby application calculates 44.85 mpg. I have been keeping records since we received delivery of the Prius in October 2009. The mpg calculation comes from miles and gallons used. The miles come from the same source, the odometer. But the gallons used come from the gas pump and the method use by the Prius computer. I suspect the Prius computer and the gas pump are not in agreement. By the way, how does the Prius computer calculate fuel consumption?

This is still better than my 2008 Toyota Tacoma which get about one half the Prius mileage.

 

Forget about the calculated mpg if your gas tank has a bladder. the computer mpg is more accurate.

 

Last fill up read 48.2 and calculated 45.5

Around 6% diff.

 

That is what I am seeing, with multiple checks. My car must be a gas hog, though. My "lifetime" average is only about 47 (actual calculated from fill ups), while others are reporting near 60. OK, it's probably my driving that makes my car a gas hog.

 

I don't see that, at least not for accumlated mileage. Do 3 or 4 fillups, record what you put in, and how far you went, do the math, and you will get an accurate fuel economy number. Variations in tank-to-tank fullness at fillup will cancel out over multiple fills.

 

I have a brand new 2011 prius and I'm seeing the same issues on my first 4 to 5 tank fill ups. I'm using fueleconomy.gov to track my MPG. I'm tracking my MPG based on hand calculated and comparing to the computer MPG. These are so far my findings:

Odometer Gallons Hand MPG Computer MPG Diff
621.6 8.86 NA NA
1089 8.59 54.4 58.1 3.7
1618 9.65 54.4 58.4 4.0
2052 8.04 53.9 57.8 3.9

I have used the same gas station and pump on all these fillings and I'm getting around 4 MPG difference between hand and computer derived MPG values. But still, it is much better than the 22MPG that I was having on my previous car.

 

charlie_rivera1 I see that unfortunately you get about 6% discrepancy - pity that Toyota's MFD is so off...2-3% would have been OK, but >5% is a bit too much for my liking...
PS: congrats on your very good MPG!

 

Using multiple checks, I find my Prius MPG calculator to be about 5-6% high, which is pretty much in line with other cars I've had, including GM, Chrysler, VW, and, most recently, MINI. All car companies make them read high. I'd rather they didn't, but that's the way it is.

If you really want to know the MPG you are getting, check the odometer accuracy (mine is very close), and calculate your MPG from multiple fillups. With the Prius' high MPG and small tank, one tank is certainly not enough to get a good check.

 

I'm getting to be a broken record, but: Honda underestimates mpg, at least with the HCHII.

 

My 2006 Corvette averaged 1% low when I checked it for 10 consecutive tanks.

 

Maybe I should know, but what's an HCHII?

 

The GM cars I had which read high were a '98 Grand Prix and an '06 Malibu Maxx.

 

Sorry: second generation Honda Civic Hybrid, model year 2006 & onward. They're just reviewing the 3rd gen at CleanMPG, and it seems to be following the tradition of under-reporting mpg. It's a mixed review though: good mpg for the average driver, but frustrating for the avid hypermiler testing it.

 

I have a new 2011 blizzard IV with Solar
I have 650 miles on her
two half tank top offs.
Calculated 49.3 MPG
dashboard reading is 49.1

very close!! and THRILLLLLLED with my mileage thus far on 50/50 highway city
in Florida with AC on 90 percent of the time.

WOW

 

Just finished a 350 mile trip in my new Prius, four weeks and 3000 miles on OD. Started with under 100 miles. Trip included mountains for 100 miles, 55to45 mph speeds. Used ac for 100 miles of trip and power mode to climb. the rest was 250 miles of interstate driving. Cruise set at 72 most of the time. A few passes at 80 plus mph, and cruise for maybe 50 miles at 75. Combined fuel mileage is 59.3 on computer. I'll check actual when I fill up, but usually the actual calculated mpg is about 1 to 2 mpg lower than computer. I love the car, and I have, and in the past have always driven big sport UTE's and lifted 4x4 trucks. My friends and family are shocked, I bought two 2011 new Prii, one for wife too.

 

Have had my 11 prius 4 since July so only have a couple of tanks and my expectation is also that the first few tanks are breakin. With that said, I do almost all my driving in Houston with an overall average of about 29 mph.

My current rule of thumb has been computer readout of 53.5 is about 50.5 and 56.5 is 53.9 (my best tank so far).

I base my actual measurements using the actual traveled computer miles divided by the number of gallons I put in (typically 9.5 to 10). I stop right after the pump clicks.

 

Ours is also off by about 3.5 mpg fairly consistently. The 2006 Honda Civic hybrid always read 1-2 mpg in the negative. So if the computer read 50 mpg you were actually obtaining 51-52 true calculated mpg's. Just the opposite of toyota...

 

It seems to me that my delta is getting worse....last one was 8%... I also firmly believe that they steal fuel at the tank by showing bigger volume than what they actually sell (but they have to be careful because if somebody ends up fuelling more than the tank....)...