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mpg shot up over past few days

Discussion in 'New A3/S3 (8V Chassis)' started by cemerson, Mar 10, 2014.

  1. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    The mpg in my car has really gone up over the past few days, by 10 or 15%. It seems to have coincided with the recent warm weather, but I'm not entirely sure. I normally fill up at Sainsbury's but put £30 of shell fuel in on Friday, so could be that as well. Or it could be that my engine has suddenly decided it's done enough miles and loosened up all of a sudden, but that seems unlikely - I've done 9000 miles now. I've also recently turned off my heated seats after being on every time I drive nearly all winter, but that was a while ago so don't think it's that.

    Anyone else with the 2.0 TDI seen anything similar in the warm weather? Going to continue trying different things to find out what it could be, whether it's the fuel or the weather!
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  3. Snook
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    Snook Mr_Snook

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    [Mar 10, 2014]
    What's it quoting on average? Can't wait to collect mine end of April!
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  4. Daveotto
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    Daveotto Well-Known Member

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    [Mar 10, 2014]
    Not noticed an increase yet on my 2.0TDI yet. But did noticea slight drop of about 2 mpg as me moved from Autumn into Winter just after I got the car but put that down to being more liberal with the accelerator once the engine bedded in.

    On my previous 1.4TFSI petrol there was always a 2mpg difference between summer and winter driving
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  5. NickC84
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    NickC84 Member

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    [Mar 10, 2014]
    Highly likely to be the warmer weather, my MINI has done the same.
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  6. Migwire
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    Migwire Member

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    [Mar 10, 2014]
    Doesn't cold air, being denser hold more oxygen? Therefore I'd have thought it would run slightly better in colder weather. Probably offset though by the greater demands on the electrical systems though. I'm just theorising here though so could be wrong.
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  7. NickC84
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    NickC84 Member

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    [Mar 10, 2014]
    Humidity plays a factor but primarily its will be the time it takes for the engine to heat up and electrical system as you say.
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  8. Gazwould
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    Gazwould Active Member

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    [Mar 10, 2014]
    Definite improvement since warmer weather .
    #7
  9. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    A journey (80 miles) that I was getting ~48mpg on previously shot up to 54mpg on Friday, and my work trip (usually 47 - 48) gave 53 today, and I wasn't even trying! Got 54 on the way home on Thursday without trying too hard as well, and it's usually rare that I barely scrape 50 (queue to get out of Loughborough, A roads and villages in between, queue to get in to Nottingham... although it does do very very well setting at 30 in 3rd or 40 in 4th on the ACC without any disturbances).

    On my old petrol it definitely performed better in Winter because of the denser air, not sure it was more efficient though. I suspect the temperate of the fuel in the tank makes quite a big difference over most other things.
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  10. M_D_O_London
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    M_D_O_London Member

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    [Mar 10, 2014]
    I also saw a moderate improvement on mpg for my car this weekend, all be it a 1.8 TFSI S-Tronic, and not a TDI.

    Was doing a run to Heathrow and back and was getting 51 MPG on the motorway section (climate control off, no windows open and with the roof open slightly on tilt) - didn't go over 75 at any point.
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  11. s3_trev
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    s3_trev 3 door or no door!

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    [Mar 10, 2014]
    This is where my money would be going. I wouldnt take any car near a supermarket for fuel, if that tells you anything. I think there is a few threads on this very subject on these forums.
    #10
  12. desertstorm
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    desertstorm Well-Known Member

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    [Mar 10, 2014]
    Been driving diesels for several years now and this is typical.Diesels are so much more efficient than petrols that they take longer to warm up especially when it's cold. I have found that as soon as temperatures hit 12-15 degrees the car starts warming up quicker and you start to see better fuel economy. However when it gets too hot over 20-22 degrees it gets marginally worse.
    Also helped by things like the supplementary electrical heater not having to do anything glow plugs not running for longer. You will probably find the pressure in the tyres up a bit as they will be hotter.
    Shell fuel is better than your average supermarket stuff as well.

    Sweet spot is around 18 degrees.

    Karl.
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  13. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    I have a heavy right foot at points, and wasn't really trying for economy, didn't even take the motorway back yesterday, used the A5 with all its roundabouts instead to make the journey a bit more interesting, wasn't even thinking about economy - but it was still up there!
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  14. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    Why is that I wonder?
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  15. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    I'm not convinced - mpg started shooting up on Thursday, but I visited Shell on Friday. Could be a coincidentally economic journey just before I filled up but I'm not convinced.
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  16. warren_S5
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    warren_S5 Moderator Staff Member Moderator VCDS Map User

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    [Mar 10, 2014]
    Colder weather means the cold start ends up fuelling the car more heavily to offset the cold dense air.

    In the olden days when people had pitchforks and such the like it was called using a choke, then in the 80's when EFI came to prevalence a fifth inject / cold start valve was used to keep engines running smoothly until they got up to temperature. These days all that jazz is likely just controlled by the HPFP/ECU. The warmer the ambient air temps get the less reliance there is for excess fuel to offset the cold dense air, hence MPG will increase marginally.

    Not sure why in extreme heat MPG would drop again???
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  17. Pasper2
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    Pasper2 New Member

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    [Mar 10, 2014]
    Our company vans Mercedes Sprinters return a better mpg on Shell diesel if thats any help
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  18. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    By how much though? Surely not 15%...
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  19. Pasper2
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    Pasper2 New Member

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    [Mar 10, 2014]
    No its approx. 10%, the rest might be due to the warmer weather?
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  20. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    I had just over half a tank when I put the shell fuel in there, so it's mostly Sainsbury's fuel anyway, with the shell fuel mixed in, and like I say - the mpg started improving before I put any shell fuel in. I'm not convinced fuel makes that much of a difference with a diesel to be honest. With petrol - yes, but not diesel.

    Assuming the weather stays pretty constant, I'll start using Sainsbury's again to see what happens.
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  21. warren_S5
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    warren_S5 Moderator Staff Member Moderator VCDS Map User

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    [Mar 10, 2014]
    ECU's need to adapt to fuel, you don't get a magical MPG boost. The fuel that is in there may burn a bit cleaner and more efficiently, but 10-15% increase.... their marketing teams must be clapping their hands together!

    How about one of these: HowStuffWorks "10 Fuel-saving Device Hoaxes"
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  22. dieselguy
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    dieselguy Member

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    [Mar 10, 2014]
    Last night I noticed on a motorway run (200 miles) I got 54.8 mpg. The same trip in January I got 51.4 mpg. So maybe there is a slight difference.
    However, there are too many factors than just temperature outside. I had a full car load last night with Shell V-Power Diesel compared to an empty car in January with BP normal Diesel.
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  23. adamss24
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    adamss24 Well-Known Member

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    [Mar 10, 2014]
    It's a mixture of things: summer diesel, hotter weather and timing advance all will result in better Mpg...
    #22
  24. Flibble
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    Flibble Member

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    [Mar 10, 2014]
    Diesel engines are also physically heavier and so take more energy to heat up due to greater mass of metal.
    Not sure on the high temperature thing, air con in use?
    #23
  25. Anarch
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    Anarch Member

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    [Mar 10, 2014]
    A bit off topic - I've collected the car last Saturday and the average mpg seems to be working fine, but the one that should indicate current fuel consumption is completely crazy - it seems to be showing a completely random reading every other second. How does it work in your cars ?
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  26. warren_S5
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    warren_S5 Moderator Staff Member Moderator VCDS Map User

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    [Mar 10, 2014]
    Is average, and the other is real time?
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  27. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    Well yes, current fuel consumption does vary wildly, so it reflects that! It's only really helpful if everything is 'stable' - you have constant pedal pressure, constant gradient, constant wind / airflow, constant road surface etc... all these things can really affect it.
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  28. Anarch
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    Anarch Member

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    [Mar 10, 2014]
    I did figure that much out - I knew it could vary. Taking into account that it's a new engine, I would assume that the mpg would vary between 40 - 31 mpg depending on the conditions you've mentioned. But spontaneously jumping from 1412 - 24 mpg (0.2 - 12 l/100km) is rather weird. I also don't think that running engine can at any point do 1412 mpg.
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  29. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    if you are covering miles but the engine is using no fuel (eg, coasting or going downhill), you are doing 'infinite' mpg at that moment. Never seen 1412 though, mine goes up to 300 then turns to 3 dashes ('---') to indicate it's too high to measure I guess!
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  30. Anarch
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    Anarch Member

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    [Mar 10, 2014]
    I actually had it set to l/100km (It's more intuitive for me) and I did a quick conversion to mpg for you guys - that's probably why I didn't get 3 dashes. I'll have a look at this while on a highway and see whether it stabilizes.
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  31. cemerson
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    cemerson Well-Known Member

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    [Mar 10, 2014]
    On a flat surface with cruise control on (or a steady foot) it stays roughly constant, though still changes every second or so. The only reason it doesn't update faster than that is because the display has to have a limit at how often it updates!
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  32. Anarch
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    Anarch Member

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    [Mar 11, 2014]
    Thanks - I'll give it a go
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  33. cemerson
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    cemerson Well-Known Member

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    [Mar 19, 2014]
    Well, went to Newcastle yesterday (from Nottingham) in the morning using ACC all the way up the motorways and A roads, and arriving in Newcastle just before 9am (ie, rush hour - lots of queueing), and still managed 61.7mpg :D Drove home today, this time leaving Newcastle during rush hour (to Loughborough) and managed 56.6mpg, though it was very windy so that may have had something to do with it! The entire lot (plus work and back on Monday) took out only 3 lights on my fuel gauge too.

    Pretty happy with that!
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  34. smk82
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    smk82 Member

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    [Mar 19, 2014]
    Will be interested to see what it works out when you manually calculate at fill up time..
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  35. cemerson
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    cemerson Well-Known Member

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    [Mar 19, 2014]
    Yeh, not really done a proper brim to brim test like that yet - but the mpg and the fuel guage tally with each other so they must be fairly close.
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  36. dieseldoug
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    dieseldoug Member

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    [Mar 19, 2014]
    Dieel engines warm up very fast due to the cooling size and water flow across the engine alone with the thermostat and the electric heater. Fuel economy is usually best with garage fuel and not supermarket fuel we do see 64 mpg on the A3 and A1 the Q5 is now showing constant 38 mpg compaired to 32 mpg so all looks good
    #35
  37. cemerson
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    cemerson Well-Known Member

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    [Mar 22, 2014]
    Hit 518 miles when the fuel warning came on today... with another 45-50 miles to go. 570 miles from my tank makes me happy :)

    And even then, there is always some spare when you are done, so may well have made the 600 mark. Especially as I haven't exactly been 'driving for efficiency' over the past couple of days...
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  38. cuke2u
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    cuke2u Well-Known Member

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    [Mar 22, 2014]
    I have a test I do with my car, to compare the mpg with my previous remapped Mk3 1.6 Ecoboost Focus. It's not really real world motoring but it does demonstrate the under certain conditions the manufacturers quoted figures can be achieved if not exceeded. I fill the car up with fuel, supermarket, then drive the 5 miles home, not driving like a granny and keeping to the speed limits but short shifting. The result was my old Focus used to get 57-59mpg consistently, but my A3 managed 85mpg driving it the exact same way the first time I tried it....
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  39. steviedr
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    steviedr Member

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    [Mar 22, 2014]
    Managed average 64mpg at 70mph on flat motorway, very surprised and pleased!
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  40. Daz Auto
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    Daz Auto Active Member

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    [Mar 22, 2014]
    ... now you're talking. I average around 600 miles per 55L tank from the Mk6 GTD. Looks like you are going to beat that with a 50L tank.

    I did hit the 0 miles warning after 630 miles driving once. I think it was maxol fuel. Though it has not happened since. Maybe it got colder. Usually the 0 warning is between 570-600 miles. The most I have driven after the 0 miles warning is 30 miles with the heater off, aircon off, radio off. Never doing that again. My 55L tank held over 57L :eek:

    This thread was making me think of Charlton Heston in True Lies, "So far, this is not blowing my skirt up gentlemen."
    #39
  41. cuke2u
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    cuke2u Well-Known Member

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    [Mar 22, 2014]
    It is colder, today it didn't get over 10c...
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