Mpg When Driving The Prius "normally"

[DrCez]

Your error sounds about right.

In my case the computer mpg is just over 7% optimistic. This varies quite a lot between individual tanks, from 2% to 12%. So my overall true consumption is 56.6 mpg, while the computer figure is more like 60.7 mpg.

The previous Gen II was closer, with an error of 3% (true 55.4mpg, computer 57.1), but a much wider variation (from -6% to +14%).

If you think that the Gen III fuel consumption isn't much better than the gen II, that's because, over a similar timescale, the Gen III has seen two winters, while the Gen II was just one. And of course, correspondingly less summer.

Just to back up your findings, the statistics for my Gen III are showing a very similar trend.

Overall true consumption (from Fuelly/spreadsheet): 50.5 mpg; computer figure: 53.8 mpg; error: 6.4%

Also my discrepancy for individual tanks is similar, ranging from 0.9% - 12.9%. Some variation will be due to differences in how full I end up filling the tank each time but it is interesting that the Prius always overestimates the mpg compared with the tank-to-tank calculation. The great thing about things like Fuelly is that the long term average gets more and more accurate so it is quite clear that the Prius systematically over-estimates mpg.

When using fuelly we are assuming that the volume of fuel delivered and the distance covered by the car are accurate but my impression is that these two parameters are reliable.

[Ancient Nerd]

When using fuelly we are assuming that the volume of fuel delivered and the distance covered by the car are accurate but my impression is that these two parameters are reliable.

Yes, I think those two are accurate. Petrol pumps are calibrated regularly, and I think car odometers don't have the inbuilt 10% error. The dynamic measurement of fuel used is probably less accurate, although the consistency between our experiences suggest it's proably not as bad as I would have expected.

The other thing that is not easy to confirm, but I am sure is true, is that the mpg figures read higher after you've filled the tank, and gradually reduce towards the end of the tank. I must try confirming that somehow.

In the same vein, the estimated range also tends to reduce as the tank empties. And before you say it, I mean the tank range, not the miles left to empty

It seems that the hardest thing to measure here is the amount of fuel in the tank, which is needed for the range. Does anyone have any idea how this is measured?

[Jan&tone]

The measurement of fuel remaining in the tank must be very difficult.

Most, if not all, garages are level and if you are filling the tank it's simple, it's either full or it isn't. But, when you park on a hill, or on a steep camber what happens then. "how is the measurement done" is a good question!

[dwilson]

but it is interesting that the Prius always overestimates the mpg compared with the tank-to-tank calculation.

This is not the case for my Gen 2 Prius

David

[jont-uk]

Been 65+ indicated over last week or so - run to Coventry yesterday saw 69 - Liz's weekly run to north Kent gets around 60 - better than the 35 from the Mercedes !

Jon

[Doesn'tExist]

maybe your missus should teach mine on how to drive.

[Ancient Nerd]

but it is interesting that the Prius always overestimates the mpg compared with the tank-to-tank calculation.

This is not the case for my Gen 2 Prius

David

Agreed. My Gen II varied over a range of -6% to +14% (average 3%) over 40,000 miles. So it only overestimated around 80% of the time

On the other hand in 45,000 miles, the Gen III (2.1% - 11.6%, average 7.2%)has NEVER underestimated the mpg.

[DrCez]

I found this link where bwilson4web presents some actual vs. indicated mpg data from PriusChat for the Gen 3 Prius:

http://ecomodder.com/...9840.html

His best fit line through the data is

actual = (.85 * indicated) + 5.3, converting to UK gallons that's

actual = (.85 * indicated) + 6.32

Using this line gives the Gen 3 error at 50 mpg as 2.3% and 4.4% at 60 mpg - slightly better than what I am seeing but backed up by more data.

It seems that the hardest thing to measure here is the amount of fuel in the tank, which is needed for the range. Does anyone have any idea how this is measured?

According to the references below, fuel tank level is determined from the position of a float in the fuel tank. When the tank is full, the float is pushed up against the top and cannot move down until the fuel level drops lower than the bottom of the float, so the gauge remains on full for a while after brimming the tank. When the tank nears empty, the float may ground on the bottom of the tank at which point fuel level can no longer be measured. The car's computer can correct the gauge measurement for a non-uniform tank shape, and even out variations as the petrol sloshes around the tank.

I don't know if the Prius uses this system but it does tally with the observation that the fuel gauge stays on 10 bars for a while when the tank is completely filled.

http://auto.howstuffworks.com/fuel-gauge.htm

http://en.wikipedia.org/wiki/Fuel_gauge

[Jan&tone]

Mpg when driving normally?

Yesterday, A130 Pitsea to Chelmsford, A12 to Ipswich, A14-a140 to Cromer, 63.6 mpg.... I'm happy with that!!

[Grumpy Cabbie]

I like this one - Harrogate center to Leeds center - 16 miles at 80 mpg or there abouts. Not bad for a Mondeo sized automatic petrol car!

[AEB-UK]

I like this one - Harrogate center to Leeds center - 16 miles at 80 mpg or there abouts. Not bad for a Mondeo sized automatic petrol car!

Was this downhill most of the way?

What was the MPG on the return journey?

[Grumpy Cabbie]

It was downhill some of the way yes. If you know the area there is a mile long hill down Scott Hall Road A61 from the B6159 roundabout down to the BMW garage. It's great as it gives you a full Battery so you can make the following 2 miles on mostly EV.

To balance this though, there are a few smaller hills from Harrogate and then the half mile long hill UP Harewood Hill (a mile from Harewood Hill Climb Club!), so I'm not cheating. ;)

Sure I could have shown the economy from the top of Beamsley Hill (nr Skipton) all the way downhill to Harrogate (about 15 miles) and show 100 mpg but that really would be cheating

Obviously one can choose the route you want to show the Prius at its best, but you I GUARANTEE you couldn't get anywhere near 80 mpg on that same route out of a diesel Mondeo with manual transmission let alone an automatic petrol. I doubt you'd get it out of anything other than maybe a Smart diesel and even then I really doubt it.

Perhaps there should be an eco challenge among taxi drivers?

[kithmo]

It was downhill some of the way yes. If you know the area there is a mile long hill down Scott Hall Road A61 from the B6159 roundabout down to the BMW garage. It's great as it gives you a full battery so you can make the following 2 miles on mostly EV.

To balance this though, there are a few smaller hills from Harrogate and then the half mile long hill UP Harewood Hill (a mile from Harewood Hill Climb Club!), so I'm not cheating. ;)

Sure I could have shown the economy from the top of Beamsley Hill (nr Skipton) all the way downhill to Harrogate (about 15 miles) and show 100 mpg but that really would be cheating

Obviously one can choose the route you want to show the Prius at its best, but you I GUARANTEE you couldn't get anywhere near 80 mpg on that same route out of a diesel Mondeo with manual transmission let alone an automatic petrol. I doubt you'd get it out of anything other than maybe a Smart diesel and even then I really doubt it.

Perhaps there should be an eco challenge among taxi drivers?

I did once get 76 mpg showing on the trip with a manual Mk3 TDCi Mondeo coming from Hornsea down to the M62, it soon dropped to it's usual 56 mpg when I was cruising at 70 mph on the M62 and down the M18 though.

[Jan&tone]

Mpg when driving normally?

Yesterday, A130 Pitsea to Chelmsford, A12 to Ipswich, A14-a140 to Cromer, 63.6 mpg.... I'm happy with that!!

On the return trip i used trip monitor B, 68.5 mpg, but there was 4 miles of jams which let me use EV all the time!!

Trip A, which was the total of the trip up, running around in Cromer/Weybourne/Wroxham and the trip back has given me a total of 62.8 mpg over 342 miles of varying road types.

Who couldn't be happy !!

[kithmo]

Yesterday I went from Rotherham to Grosmont (near Whitby) and averaged 68.7 mpg (on the trip) on the outward journey, driving normally, as in keeping up with traffic and up to speed limits. The return journey dropped the average to 67.2 mpg for the overall journey (more motorway on the return leg and some 75-80 mph stints on A1M).

I was pleasantly suprised at how easily it went up the 1 in 3 and 1 in 4 hills around Grosmont and how well the transmission held the car back, down the hills, in "B" mode.

[johalareewi]

Maybe we should head over to Mr T and take part in the latest promotion...

Bags I go when it is really warm and sunny :)

http://www.toyotaownersclub.com/news/date/2011-04-07/title/toyota-hybrid-challenge-how-low-can-you-go

[Carltona123]

Oh that the weather was always this warm!

I drove from Solihull down to Banbury on Saturday afternoon. Kept to A roads, drove at the speed limit. Hardly any flat bits - some very big hills and a slow crawl hrough Stratford. I know it was only a short run but my 70 mpg (indicated) was more than acceptable.

M

[Andy in Bristol]

On Sunday, I drove from Bristol to Wiltshire and back. No motorways, and the temperature was over 20 degrees. Can you believe I got better than the officially reported figures over a distance of 80 miles? Take a look for yourself...

I'm well impressed!