Is this a good fuel consumption

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#1285136 15-Apr-2015 21:25

joker97: In lab conditions or real life? Very different numbers you'll find

Interestingly enough the Mazda 6 does very close to the numbers they describe. Our lease company monitors this across their fleet and it's within 0.2 l/100kms from memory. This is for both diesel and petrol. They are the only brand that seems close to their claimed number.

alasta

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#1285138 15-Apr-2015 21:27

My vehicle manufacturer quotes 6.4l/100km as the combined consumption. My own combined consumption with minimal city driving is about 7.4l/100km but I can manage around 6l/100km on a trip. The manufacturers' figures don't reflect what you will achieve in the real world but the methodology is consistent so at least you can make a meaningful comparison between vehicles.

Interestingly the trip computer in my car seems to understate fuel consumption, although I've never tested it scientifically. The figures that I have quoted above are calculated from my log book.

1eStar

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#1285441 16-Apr-2015 10:57

alasta: My vehicle manufacturer quotes 6.4l/100km as the combined consumption. My own combined consumption with minimal city driving is about 7.4l/100km but I can manage around 6l/100km on a trip. The manufacturers' figures don't reflect what you will achieve in the real world but the methodology is consistent so at least you can make a meaningful comparison between vehicles.

Interestingly the trip computer in my car seems to understate fuel consumption, although I've never tested it scientifically. The figures that I have quoted above are calculated from my log book.

From my testing the quoted fuel usage on an in car display are inaccurate. Some have a tank average but most seem to display optimistic feel good numbers. It's quite difficult to get true readings for even a tank average as even a litre variation in your "fill" can throw results wildly. Even if you try to fill it to the brim (btw not recommended) it's dependant as to whether the car is level, loaded etc. to have certainty that it's really "full". You need to average your fuel usage over several tanks to get a picture of your cars real economy.

The most economical car I drove recently for an extended period was a 2006 Toyota vitz 1.5 cvt. Regularly would do 600km on 35litres. 5.8 l/100km

MikeB4

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#1285456 16-Apr-2015 11:02

The quoted figure by the manufacturer is pointless really. So many factors affect consumption rates, temperature, road conditions, traffic conditions, fuel quality, condition of the vehicle, tyre pressure, weight being carried use of accessories and driving habits.
The car displays are good to indicate how one is going with regards to economy in general but really not accurate.

heylinb4nz

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#1285479 16-Apr-2015 11:30

KiwiNZ: The quoted figure by the manufacturer is pointless really. So many factors affect consumption rates, temperature, road conditions, traffic conditions, fuel quality, condition of the vehicle, tyre pressure, weight being carried use of accessories and driving habits.
The car displays are good to indicate how one is going with regards to economy in general but really not accurate.

The best car display to use is the trip meter

(Litres of Fuel to fill up / Kms travelled) X 100 = litres per 100 km

I typically do this on a Hamilton to Auckland run, fill up do a return trip, fill up again....and take note of the driving style. This give me Highway mileage.

When partner uses car to go to and from work during week, I fill it on Friday night and this gives me city mileage.

For mixed I record those as well and over course of a year get a mixed average.

Doing this gives you 3 base line figures which you can then monitor against to know if something is amiss with your car.

Jase2985

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#1285529 16-Apr-2015 12:28

1eStar: . Even if you try to fill it to the brim (btw not recommended)

care to explain why?

garvani

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#1285536 16-Apr-2015 12:33

Currently sitting on 5.4l/100km for my 2014 Jazz hybrid (CVT vtec 1.3ltr). Thats probably around 80% town driving, i don't have a light foot either heh heh so could get it down further but when you have a fuel card why bother.

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old3eyes

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#1285561 16-Apr-2015 12:53

My wife's 2013 Toyota Corolla 1800 motor is currently on 6.7/100 metro driving and goes down to about 6.3 / 100 on a trip. My 2008 Mondeo 2.3 liter motor sits at around 10.9 to 11.5 city / motorway driving. haven't done a long distant trip in it yet..

Regards,

Old3eyes

DravidDavid

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#1285584 16-Apr-2015 13:23

Jase2985:
1eStar: . Even if you try to fill it to the brim (btw not recommended)

care to explain why?

I'm not sure if there is more than one reason. But a lot of modern cars have one or more sealed flaps before the actual petrol storage tank to keep dust and contaminants out. If you fill it right to the top, you risk forcing that valve open and washing dust, dirt and grime near the top of the filler cap in to the tank. Not such a bad thing if done once or twice I guess. But it builds up over time.

If you've got a dusty dirty driveway like mine, it's definitely not good!

Batman

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#1285596 16-Apr-2015 13:35

The car computer does not measure all the space in your tank so amount and distance is not accurate

Fuel consumption is measured at fuel delivery or fuel pump so it is very accurate

Jase2985

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#1285608 16-Apr-2015 13:49

joker97: The car computer does not measure all the space in your tank so amount and distance is not accurate

Fuel consumption is measured at fuel delivery or fuel pump so it is very accurate

generally speaking a fuel pump is pumping all the time, at a fixed rate (with reason) so its not that

it would be injector duty cycle x flow rate of injectors for fixed value of fuel pressure, then distance traveled/speed of vehicle

complex calculation :)

Batman

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#1285638 16-Apr-2015 14:38

ok my bad, but my fuel consumption is pretty accurate.

don't forget that when we calculate fuel consumption ourselves, there are many inaccuracies namely
- how much fuel you think you've put it. every pump stops giving fuel inconsistently, possibly every time too, depending on the person doing it.
- there is more fuel when it's cold, and less fuel when it's hot.
- etc

RUKI

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#1285663 16-Apr-2015 15:17

joker97: The car computer does not measure all the space in your tank so amount and distance is not accurate

Fuel consumption is measured at fuel delivery or fuel pump so it is very accurate

At the fuel delivery (i.e. injectors)
Not at the fuel pump. The pump's role is to create constant pressure in the fuel rail, excess is discarded back to the tank.

In new cars it is easy to monitor via OBD-II scanner

Fuel consumption is mesured by monitoring the total time (variable) of the injector being opened and the known (constant) injector throughput.

In old school Toyotas (pre-OBDII) e.g. Starlet 98 or Carina ED 97 or the like there is also a way to monitor fuel consumption.
I've been offereing a solution a while ago - was popular (plug and play cable + soft) among other metrics (including RPM, Oxygen Sensor performance, Temp etc) it was capturing the fuel consumption. Manual entry of the injector performance was required to calculate consumption with high accuracy.

I can make that tool again if needed.

Jase2985

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#1285708 16-Apr-2015 16:21

joker97: ok my bad, but my fuel consumption is pretty accurate.

don't forget that when we calculate fuel consumption ourselves, there are many inaccuracies namely
- how much fuel you think you've put it. every pump stops giving fuel inconsistently, possibly every time too, depending on the person doing it. This is true but if you fill your tank up till you see the lever of fuel every time this minimises the inconsistencies.
- there is more fuel when it's cold, and less fuel when it's hot. highly unlikely, the fuel is stored in an underground tank, and there is thousands of liters in there so the outside tempertaure isnt going to make much of a difference when putting it into your tank. as for putting it into your motor it will make minimal difference. not to mention NZ doesnt have very big tempertaure swings like other countries

see above for some replies to your points

1000 gallons of fuel cooled by 25 degrees ends up being about 990 gallons, so reducing it to car sized volumes, 10 gallons to 9.9 gallons, which is about 0375L so next to no difference.

the fuel pump will warm it up a little when being pumped, the fuel rail will be warm as it on top of the engine, so by the time it gets into the engine it will be warm again :)

Azzura

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#1285726 16-Apr-2015 16:42

Mazda M2 averages about 6.6l/100 driving to Auckland and back. But usually it is 7.6l/100.

I picked up one of these years ago -

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