Fuel consumption- computer vs actual




Results 1 to 17 of 17
  1. #1
    Join Date
    Apr 2014
    Location
    Krugersdorp
    Age
    40
    Posts
    389
    Thanked: 231

    Default Fuel consumption- computer vs actual

    So I filled up my Navara today, thinking about the fuel consumtion displayed on the computer, how accurate is it? Or is the manual calculation better? Now my car’s GPS when drving shows about a 5% lower speed than the speedometer so it should translate to the same variation in distance therefore fuel consumption.

    When calculating manualy it came to 10km/l where as the computer was showing 10.8.

    Not that its that important, but just for interest sake.

    Which would be the most acurate?
    Nissan Navara d23 (Leatherman)
    Jeep Cherokee 3.2 (Swambo’s sportscar/ mommy taxi)

  2. #2
    Join Date
    Sep 2010
    Location
    Brymore, Port Elizabeth
    Age
    57
    Posts
    758
    Thanked: 20

    Default Re: Fuel consumption- computer vs actual

    Speedometers usually over-reads, whereas odometers are more accurate.

    On diesel vehicles the computer opens the injectors for a specified time, during which diesel is injected. Pressure and orifice size determines how much diesel is actually delivered, while the computer calculates fuel consumption on the amount that would have been injected at normal pressure through normal orifice.

    On my original injectors the computer displayed a consumption worse that actual. Seems the replacement injectors have bigger holes delivering more fuel per injection period, having the computer displaying a better consumption than actual.
    Last edited by BarOne; 2018/07/02 at 09:13 PM.
    Pieter
    ------
    2008 Fortuner 3.0 D-4D 4x4

  3. #3
    Join Date
    Mar 2008
    Location
    De Wildt
    Age
    56
    Posts
    30,226
    Thanked: 6336

    Default Re: Fuel consumption- computer vs actual

    You GPS is accurate to a couple of meters. Your speedo, odo and fuel flow sensor is not.

    The only way to determine true fuel consumption:

    - fill tank to first click
    - reset trip data on GPS
    - drive until reserve light comes on
    - fill up to first click
    - record liters and trip kms
    - repeat x 2

    you now have a running average which is 700 millionty trillionty times more accurate.

    Your onboard consumption indicator is just that, an indication, not reality.
    2012 Jeep Sahara Unlimited 3.6 V6
    Ela Diablo: Land Rover S2A 109 PUP: SOLD

  4. The Following 2 Users Say Thank You to jelo For This Useful Post:


  5. #4
    Join Date
    Jul 2011
    Location
    Durban
    Age
    54
    Posts
    4,411
    Thanked: 418

    Default Re: Fuel consumption- computer vs actual

    Quote Originally Posted by jelo View Post
    You GPS is accurate to a couple of meters. Your speedo, odo and fuel flow sensor is not.

    The only way to determine true fuel consumption:

    - fill tank to first click
    - reset trip data on GPS
    - drive until reserve light comes on
    - fill up to first click
    - record liters and trip kms
    - repeat x 2

    you now have a running average which is 700 millionty trillionty times more accurate.
    Your onboard consumption indicator is just that, an indication, not reality.
    I dunno, my Fortuners computer was very, very accurate when compared to the tank to tank calculations that I did over two years.
    EDIT: Not using the GPS
    Last edited by dirtshark; 2018/07/03 at 09:51 AM.
    FJC - Just Cruising

  6. #5
    Join Date
    May 2011
    Location
    Pretoria
    Age
    49
    Posts
    555
    Thanked: 425

    Default Re: Fuel consumption- computer vs actual

    The difference between my 2.4 GD6 Hilux OBC and Fuelio App is about 6% more on the OBC. Comparing the Fuelio with GPS results fairly close!
    One of the stupid mistakes in life is to underestimate peoples level of stupidity!

  7. #6
    Join Date
    Sep 2011
    Location
    durban/himeville
    Age
    55
    Posts
    110
    Thanked: 60

    Default Re: Fuel consumption- computer vs actual

    Quote Originally Posted by jelo View Post
    You GPS is accurate to a couple of meters. Your speedo, odo and fuel flow sensor is not.

    The only way to determine true fuel consumption:

    - fill tank to first click
    - reset trip data on GPS
    - drive until reserve light comes on
    - fill up to first click
    - record liters and trip kms
    - repeat x 2

    you now have a running average which is 700 millionty trillionty times more accurate.

    Your onboard consumption indicator is just that, an indication, not reality.
    I agree with this strongly and irrespective of how accurate your computer is , this can be done and only takes a small effort. Keep a notebook and pencil and jot it down. Call it back up )) I do this with favourite routes and I have a good idea what the usage is for these trips.
    Last edited by KK20; 2018/07/03 at 10:03 AM.

  8. #7
    Join Date
    Jan 2013
    Location
    Friemersheim, Southern Cape
    Age
    56
    Posts
    3,255
    Thanked: 1594

    Default Re: Fuel consumption- computer vs actual

    Quote Originally Posted by jelo View Post
    ......

    - fill tank to first click
    ...........
    Not all first click's are created equal.....

  9. #8
    Join Date
    Mar 2008
    Location
    De Wildt
    Age
    56
    Posts
    30,226
    Thanked: 6336

    Default Re: Fuel consumption- computer vs actual

    Quote Originally Posted by Prof View Post
    Not all first click's are created equal.....
    It's as close as you can expect to get outside of a lab. The couple of hundred ml's that it could deviate with are not significant enough over the distance of an entire tank. Hence my advice on 3 x to get a proper running average.
    2012 Jeep Sahara Unlimited 3.6 V6
    Ela Diablo: Land Rover S2A 109 PUP: SOLD

  10. #9
    Join Date
    Feb 2009
    Location
    Windhoek
    Age
    35
    Posts
    5,744
    Thanked: 1562

    Default Re: Fuel consumption- computer vs actual

    For me it is not so much the complete accurateness of the calculation but rather how much trust I can put into the consistency of the OBC and odo. On the Amarok I could trust the OBC to withing 0.5km/l. ON the Treg, it seems to be 0.8km/l.

    This allows me to work on the range left.
    VW Touareg V6 Tdi Escape
    Bush Lapa Boskriek 816

  11. #10
    Join Date
    Jul 2007
    Location
    Putfontein, Benoni
    Age
    50
    Posts
    1,902
    Thanked: 1168

    Default Re: Fuel consumption- computer vs actual

    I have found the actual range left display on audi/vw vehicles to be very accurate. You don't have to calculate it based on consumption, it tells you directly what you need to know.
    Audi S6 2008 - v10 Quattro
    Audi A6 Avant - 2005 - 3l TDi Quattro
    Audi Q5 - 2009 - 3l TDI Qauttro
    Audi 90 Coupe - 1995 - 2.8l V6 quattro
    VW Touareg - 2005 - V10 TDi Awd
    VW Passat CC - 2013 - 2l TDi bluemotion(repair project)

  12. #11
    Join Date
    Nov 2013
    Location
    Bloemfontein
    Age
    37
    Posts
    388
    Thanked: 62

    Default Re: Fuel consumption- computer vs actual

    I always measure from "first click to first click", not always against a GPS though. My onboard computer is not that far off an are usually more conservative. I would for instance calculate 11.6km/h, onboard computer shows 11.1/11.2.

    So for an everyday (very good) indication of what consumption I get, what range I have left, my onboard computer is more than sufficient.
    Last edited by Kambro; 2018/07/03 at 11:00 AM.

  13. The Following User Says Thank You to Kambro For This Useful Post:


  14. #12
    Join Date
    Oct 2010
    Location
    Pretoria
    Age
    59
    Posts
    1,233
    Thanked: 244

    Default Re: Fuel consumption- computer vs actual

    Disco 3 and 4 has a very optimistic fuel consumption on the computer, out by at least 10%

  15. #13
    Join Date
    Sep 2006
    Location
    Kempton Park
    Age
    51
    Posts
    13,732
    Thanked: 805

    Default Re: Fuel consumption- computer vs actual

    kombi is very accurate, no speedo error at all, Amarok the same. For also quite accurate. Drove friends v6 hilux. You get 20 but computer says 14
    Turnkey Construction Projects, Commercial, industrial, Domestic
    Importers: Diving gear, Compressed air cylinders for diving and airgun industry, 4x4 equipment.
    Manufacturers: Pofadder Kinetic ropes, Recovery kits, Synthetic winch ropes
    Vehicles: Modifications and installations, Special application vehicles
    Driver training: 4x4, Defensive
    [email protected]
    +27824453301

  16. #14
    Join Date
    Sep 2008
    Location
    Vanderbijlpark
    Age
    49
    Posts
    1,727
    Thanked: 136

    Default Re: Fuel consumption- computer vs actual

    I always keep record using the tank-to-tank logbook method. On my '15 Ranger, the trip computer is a little bit optimistic, but not by too much.
    ZS6VL


  17. #15
    Join Date
    Nov 2013
    Location
    Bloemfontein
    Age
    37
    Posts
    388
    Thanked: 62

    Default Re: Fuel consumption- computer vs actual

    It's sometime interesting to keep an eye on that real time consumption figure. For instance: although you do not feel it necessarily, a strong headwind is a consumption killer. Especially in something as un-aerodynamic a bakkie! Hard acceleration (in any vehicle) makes that figure spin like a slot-machine!

  18. #16
    Join Date
    Jul 2007
    Location
    Putfontein, Benoni
    Age
    50
    Posts
    1,902
    Thanked: 1168

    Default Re: Fuel consumption- computer vs actual

    Yup. Immediate consumption is not a display I like to put on often for the two v10's. My S6 will easily see 42-45 l/100 with your foot flat. The touareg not far from there.
    Last edited by Stephan van Tonder; 2018/07/10 at 09:33 AM.
    Audi S6 2008 - v10 Quattro
    Audi A6 Avant - 2005 - 3l TDi Quattro
    Audi Q5 - 2009 - 3l TDI Qauttro
    Audi 90 Coupe - 1995 - 2.8l V6 quattro
    VW Touareg - 2005 - V10 TDi Awd
    VW Passat CC - 2013 - 2l TDi bluemotion(repair project)

  19. #17
    Join Date
    Jun 2012
    Location
    Benoni
    Age
    43
    Posts
    775
    Thanked: 365

    Default Re: Fuel consumption- computer vs actual

    Quote Originally Posted by Stephan van Tonder View Post
    Yup. Immediate consumption is not a display I like to put on often for the two v10's. My S6 will easily see 42-45 l/100 with your foot flat. The touareg not far from there.
    I suspect zee Germans programmed the ODC to never show more than 45l/100km, I have tried a few times to get it above than number to no avail. Towing a heavy load under hard acceleration I suspect the instant consumption is a fair bit more than that
    2012 Q7 4.2 TDI
    Birkin SR20DET race car


Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •