calculated vs. computer MPG - Please post your results

Just refilled gas once it started flashing, 35 Litres, Trip Odometer showed 793 km => 4.41 L/100km = 53.33 mpg

Prius computer showed 4.3 L/100km trip average = 54.7 mpg

2.5% different.

I consider it VERY accurate considering all the unmeasurable variables such as difference in fuel temperatures between last and this fill up, unable to fill up to the exact tank level relying on the fuel pump's auto shutoff, the low fuel flashing alarm may start flashing earlier/later due to inclination of the car, etc, etc.

It was showing 4.1 L/100mpg most of the trip but last week of road conjestion/construction caused it to end @ 4.3 L/100km. Now road construction completed, I'm getting a good start with the new tank of gas showing 4.0 L/100km (58.8 mpg) all in PWR mode driving with Cruise Control mostly between 65-70 km/h (40.4 - 43.5 mph) and Neutral Glide b4 stop.

 

Our Prius mpg's are improving, thanks to weather 55 degrees and over.

Last tank 462.1 miles / 8.566 gal's / indicated mpg 56.7/ true mpg 53.945.

mixed highway and city driving. Real world.

alfon

 

Except for the 1st tank (dealer filled) I have gotten just about the same MPG. 1st tank was 3 MPG off the next 2 tanks have been just about even... I'm at 500Miles on a tank of gas and just went to last bar on gas tank gauge.

Most of my miles are city so maybe that has some bearing in it?

 

I have a 2010 Prius III, purchased 4 weeks ago.

So far (after 2,600 miles, mostly highway @65 mph), my actual (hand calculated) fuel economy has been 55.13 mpg, vs. 58.10 mpg indicated (an error of +5.3%).

 

I'm still getting used to my new car and only have 3 tanks under my belt. But so far it's about 2 MPG less. Best is 54 + MPG... But that is with 1/2 using a/c...

But I have to admit, driving slow...

 

Refill on 8/22/10. 572 miles. 8.30 US Gallons. MFD=70.1 mpg, calculated 68.9 mpg. 2.2 mpg off (all city). After fill hi-way driving. New cellphone nav has mph display 2 mph off 65 actually 63 mph. Still hard to do under 60 mpg with tires at 40/40.
Tony Renier

 

331.4 miles / 6.311 gals / indicated mpg 55.3 / true mpg 52.511

real world driving and 10% Ethanol gas / its all year long in Oregon.

alfon

 

View attachment 25286

Mixed mode driving - 40/38 tire pressure - 10% ethanol

Table is for 2010 year to date

 

My full tank results are quite similar to yours.

However it seems like short fill ups under 100 miles the MPG guage may be more accurate.

I went 79.9 miles and filled up based on the same method, slow speed, and stop at first click was 1.413 gallons for 56.546 MPG, the dash guage read, 55.8 MPG.

I would like to try it more but in this state, Oregon, you are not allowed to pump your own gas and it is quite annoying for the gas attented to pump only 1.5 gallons of gas in your car.

If it is was self serve I would try it over say 5-6 tanks based on less than 100 miles per fill up. I have a hunch that the guage would be more accurate.

Alfon

 

In 8124 miles, 7600 miles of which were on a road trip this summer, my new 2010 Prius's displayed MPG has averaged 3.9% higher than my calculated MPG, with a high of 11.7 % and a low of -0.4 %, in 21 fill-ups. That is similar to the error my 2002 had in the 131,000 miles I drove her. My displayed MPG average on the road trip was 50.5 and the calculated MPG average was 48.9 for the 7557 mile trip. Tire pressures were 44 psi front and 42 psi rear.

I made no effort to improve the mileage while on the trip; I drove at the posted speed limits of 70 mph and 75 mph on cruise control, for many hours on end with the air conditioning turned on. I saw definite improvement in gas consumption (displayed) when driving at 60 and 65. And I saw a marked difference with air temperature and road surface, too, although I don't have data to back that up. I think that it was in Oklahoma that I saw an indicated temperature of 103 F for a few hours. While driving through the Texas panhandle (east to west) I experienced a definite pull to the right most of the time that must have been caused by the camber of the road, although it wasn't visually obvious. Weird. I saw a lot of police activity in western Oklahoma and Texas, too, but not anything in Arizona, or anywhere else for that matter.

Jonathan
'10 8474 mi 49.3 Lmpg

 

Just curious - Why would you top it off if you're only down one or two pips from a full tank?

 

I wanted to check if short fillups, under 100 miles, if the mpg guage
is more accurate than say 400-500 mile tanks.

alfon

 

just finished 8 hours on the interstate with a tailwind. computer says 57mpg for 450 miles. car only has 1200 miles. seats were great and all the stuff plus 2 golf bags fit in nicely. plenty of power and very quiet at 65-70mph. this is a great ride --- the mpg is a fun bonus. saw 4-5 priuses --- they all blew by me.

 

After 19 fill-ups I'm averaging 5.7%, however it runs a pretty wide range from a high of 13.33% to a low of -2.38% ..?? oh well, at least the average seems about ... er .. well ... Average.

You can click on my current stats to get the whole picture.

 

On my 2010 III first tank I got display 52.4; calculated 50.0. What's really strange is the miles remaining on the trip screen. When it indicated I only had 10 miles left, even though I had driven fewer than 500 miles on the tank, and even though the tank is supposed to hold 11.9 gallons, I was only able to put 9.26 gallons in the tank. Anybody else ever experience this?

 

That's about normal. Around 2 gallons left when you are at 0 miles is common.

 

When I fill up our Prius on the slow speed click at the gas pump, when the pump shuts off you can still squeeze in 2 more gallons until you can see the fuel at the top of the neck with no draining. That is max fill, however many Prius owners do not fill up to that level do to damaging the fuel system somehow.

alfon

 

For my first fill up on my 2010 Prius cmputer showed 4.6L/100KM my calculated number was 4.9L/100KM ... I was happy with the mileage since I have read many posts here that indicate that your mileage will improve as the car is broken in and as I learn how to drive the Prius to maximize the fuel efficiency.

 

I have a regular trip I'm making now that is about 480 miles. Gas is cheaper where I live than anywhere else on this trip. When I near that mileage, I have zero miles left and the fuel gauge has nothing showing, not even the blinking last bar.

I fill up and put in about 9.7 gallons. I assume that I have at least another gallon left, but I don't want to find out.

I'm getting about a 2 mpg difference between computer read out and calculated mileage.

 

After five fill-ups I have decided to post my results. The results are stated in calculated mpg/computer mpg:

46.0/53.1
42.3/52.2
50.1/51.6
48.5/52.1
50.3/51.8

I then took the cumulative miles driven (1,574.9) and divided by cumulative gallons consumed (33.356), resulting in an overall calculated average of 47.2 mpg, compared to the average computer mpg of 52.2. This is approximately a 10% average difference, with the computer calculations always being high.

Of the five fill-ups, only the first two were at the same station. I also squeeze in every drop I can. The second time seems to be a fluke, but its statistical significance is minimized when I calculated cumulative totals and averages.

My Prius is less than two months old and I have driven it in hot South Carolina weather with the air conditioner blasting, excepting one 500-mile trip to the mountains. My rough estimate is about half the miles were on interstate highways and the other half is city/suburban/back-roads driving.

I drive in Eco mode about 95% of the time but otherwise make very little special effort to improve my mileage.

I will continue to compare calculated/computer mileage for at least five more fill-ups and see if the difference diminishes or remains about the same.

So far, I am happy with the fuel economy and I LOVE MY PRIUS!!