What's happened to my mpg?

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  • What's happened to my mpg?
  • Premier Icon Bregante
    Subscriber

    I’ve had a Honda FRV 2.0 Vtec for the last 7 years which has been utterly faultless over 80, 000 miles. No matter how hard I drive it has always averaged in the low to mid 30’s mpg. Over the last few weeks I’ve noticed this drop to 26. I’ve checked the tyre pressure and its just been serviced this week so is running nice and smoothly. The only other thing that’s been changed is I had a new battery about a month ago. Is it possible that the engine management system has been somehow disrupted when the battery was disconnected?

    I know it’s been cold the last few weeks but don’t think it’s ever had an adverse effect on mileage before.

    Any ideas?

    Edit: the garage checked the brakes weren’t dragging too.

    Premier Icon maccruiskeen
    Subscriber

    How are you arriving at the average? Are you going on the figures the car is reporting or are you getting all Peter Poddy about it and actually doing real sums? I tend to use hire cars a lot and usually for 1000mile motorway cruises and there seems to be some variation in the way they calculate their average and their responsiveness to changes in driving style/conditions. Some cars seem to be taking their average over quite a large range. I had a toyota earlier in the year and it took about 400 – 500 miles of gentle cruising before the reported average started to improve (it had presumably been used for a lot of town driving previously), after that it continued to rise steadily over the next 600 miles before I gave it back. It was reporting 32mpg when I got it and 49mpg when I handed it back after 1100 miles and was still climbing. So maybe the battery disconnect has introduced a blip that is still being accounted for in the average.

    Sum
    Member

    If the engine management system had been reset when the battery was changed then this can affect the engine but it shouldn’t take long for the engine management system to ‘relearn’ the correct settings. Usually you just let your car idle for a bit.

    Cold weather can affect economy as the lights and electric heated windows tend to be used more.

    Premier Icon easygirl
    Subscriber

    Do you reset your average fuel often, or do you leave it ofr long periods?
    If you leave to get a true average, it will take a while to get back to the previous average
    Because your battery has been changed the averages will have been reset

    Premier Icon Bregante
    Subscriber

    I’m simply going off the indicated mpg. I’ve only covered about 200 miles since the new battery went in so it might well be as you say and the EMS needs to re learn its settings. I’ll see how I get on. Ta

    Premier Icon myheadsashed
    Subscriber

    Cold air is more dense the warm air…add that to the extra demand from heater, fans, and lights etc

    The car is working harder also more fuel is used from a cold start in winter as it takes longer to reach temp>

    Premier Icon bruneep
    Subscriber

    or are you getting all Peter Poddy about it and actually doing real sums?

    Brilliant!

    Premier Icon Bregante
    Subscriber

    Easygirl: occasionally the car might not move for a couple of days but no longer than that. Also I tend to reset the average whenever I refill and as I say I think the lowest it’s ever returned is 32.6 over a full tank. I haven’t changed my driving habits either and it’s just a bit disconcerting to see such a marked drop.

    deadlydarcy
    Member

    I hope I don’t lose anything in Manchester and have to rely on Bizzies to find it for me. πŸ™‚

    Premier Icon Bregante
    Subscriber

    I wondered how long it would take for Dadly to turn up. πŸ™‚

    Premier Icon maccruiskeen
    Subscriber

    or are you getting all Peter Poddy about it and actually doing real sums?
    Brilliant!

    πŸ™‚ He does actually do that though and I think thats an important distinction because the cars own reporting can be bullshit.

    deadlydarcy
    Member

    Been up all morning Breggie. 😐

    (Sorry, not much hep I’m afraid but hope you’re well. πŸ™‚ )

    b r
    Member

    Maybe air filter, take it out and have a look.

    Also could be a lambra sensor on its way out, or a sticking caliper.

    tron
    Member

    Check the thermostat and temperature sensors. If the car isn’t getting warm / thinks it isn’t, then it will run a bit rich and this will put your fuel consumption up.

    Premier Icon Bregante
    Subscriber

    Brakes are fine, as above. Also new air filter fitted this week as part of the service.

    I’ll see how I get on over the next few hundred miles, am giving it a run down to the south east over Xmas so that should give a better indication.

    DD, I feel for you but it does get easier in 5 or 10 years! πŸ™‚

    PeterPoddy
    Member

    He does actually do that though and I think thats an important distinction because the cars own reporting can be bullshit.

    I do and it is. Apart from that this is a very flattering thread. πŸ™‚

    Reasons I’ve found for reduced MPG include

    Weather
    When it’s colder like it has been of late engines take a lot longer to warm up. Any journey of under about 20 miles will show this up. The longer the journey the less the effect because you spend less percentage of time running cold.

    A change in route or use
    This is the biggie as it effects everything. I’ve got a graph of something like 40,000 miles stored for out car and you can see average long term fuel consumption rise and fall over a period of months and I can tell you exactly why it happened.

    Changes in the car
    Not as in a different car but stuff like servicing, tyres etc. I noticed a slight improvement after we had the first new set of spark plugs. The engine was noticeably smoother and more responsive and this seemed to translate into better MPG. Eco tyres didn’t seem to make the slightest jot of difference but pressures do, slightly. Retro fitting cruise control made ours worse. That, I think, is partly because its not as sensitive as an OE system and partly because I’m one flippin’ light footed bar steward and I can beat the cruise at its own game.

    Personally, for the OP, I’d say there’s a slight chance it’s a mechanical issue but more like the fact that this happens all the time, but not being a geek (hello!) you’ve mover noticed it before.
    I’d be tempted to say its the weather to be honest. πŸ™‚

    sbob
    Member

    b r – Member

    Maybe air filter, take it out and have a look.

    Also could be a lambra sensor on its way out, or a sticking caliper.

    Is that a Freudian slip, revealing br’s sexy ovine tendencies? πŸ˜•

    Premier Icon maccruiskeen
    Subscriber

    I’ve got a graph of something like 40,000 miles stored

    I fear I have opened Pandora’s box!

    druidh
    Member

    Everything PP says, but a big WTF!!! to “low to mid 30’s” as an acceptable average πŸ™‚

    Premier Icon molgrips
    Subscriber

    Eco tyres didn’t seem to make the slightest jot of difference but pressures do, slightly

    Eco tyres made a big difference for me on the Passat, but not on the Prius, but I think the tyres that it came with may have been somewhat eco orientated (although they were not great tyres).

    I went from about 53mpg on my regular long route to about 58mpg, so around 10%. That was moving to Nokian H for summers and Nokian WR G2s for winter tyres, from Dunlop Sport.

    Cruise control helps me, but not because it’s light footed. Consistent speed helps a lot ime if you actually are cruising, not if you are on windy hilly routes.

    But this is not what the OP asked. Presumably he’s doing everything the same, whether that’s good or bad, but the mpg has suddenly dropped. Not sure why tha tmight be tbh but I’d guess some kind of engine sensor or injector problem or something. But then you’d expect any sensor issues to get flagged up.

    PeterPoddy
    Member

    Here you go. Off a phone app called Road Trip


    Untitled by PeterPoddy, on Flickr

    The first big rise (look at the average line, not individual figures) is from when we drove the car over a snowy winter to me driving the same route along the M4 back and forth to Bristol. Then it dips slightly as I come off that same route and switch to more varied driving, then the car gets left at home more and does a 20 mile run to reading and back it dips a bit more, but it’s still used for several longer journeys. The last few tanks have been frm when it’s being doing a regular 20 mile commute on A/B roads in cold icy weather. That’s killing it.

    EDIT
    Stats were reset on 9th November. The first three figures in 2010 are from 21 November, 6 & 24 December. Wasn’t it snowy then?
    Look at it jump after then

    Premier Icon geoffj
    Subscriber

    Been listening to any new music?

    Premier Icon geoffj
    Subscriber

    30,000+ miles a year! 😯

    Edit: 15,000 miles a year 😳

    PeterPoddy
    Member

    That’s 2 years, dates at the bottom. I was driving for work though. You can add 8500 miles to that.

    PeterPoddy
    Member

    You wanna be TRULY shocked by a statistic?
    Check this out, under the FUEL section, bottom left….


    Untitled by PeterPoddy, on Flickr

    And then add this to it


    Untitled by PeterPoddy, on Flickr

    Just under Β£6800 in fuel in 2 years
    Oh plus the the two bikes, another Β£1700 between them.

    Β£8500?

    That’s why I’m anal about fuel.

    Premier Icon bruneep
    Subscriber

    But how do you know that data is right?

    Premier Icon myheadsashed
    Subscriber

    PP thats quite good 😳

    I used to have a Discovery I was doing 45000+ a year in – stick a one infront of your fuel cost for the bill 😯

    It’s now gone…………..

    PeterPoddy
    Member

    But how do you know that data is right?

    Because I collected it using the most accurate figures available over a large number of samples spread over a large sampling time. Without fitting a calibrated speedo its impossible to be more accurate.

    PeterPoddy
    Member

    I have to point out the Omega. That mileage was in just over 3 months, the car was an old, high mileage 2 lite auto that cost Β£400. I spent Β£100 in repairs on it, I reckon it saved me Β£70 in tyre wear on the Focus above it and Β£75 for a new tyre when I got a piece of steel through one tyre that I didn’t replace, then we got Β£170 scrap for it. Less than Β£200 that car cost me, excluding fuel πŸ™‚

    Premier Icon maccruiskeen
    Subscriber

    You wanna be TRULY shocked by a statistic?
    Check this out, under the FUEL section, bottom left….

    I recently worked out that my van had been through 54,000 litres of diesel (666 tanks of fuel) when it passed its 300,000th milestone The first of those litres would have cost 77p the most recent around Β£150, so that vaguely averages to Β£54k. Thats 144 tons of CO2 which is about 80,000m3 which is approximately the volume of the Albert Hall.

    sbob
    Member

    druidh – Member

    Everything PP says, but a big WTF!!! to “low to mid 30’s” as an acceptable average

    Driving pleasure is directly proportional to fuel consumption. πŸ’‘

    😈

    druidh
    Member

    MacCruiskeen wrote:

    You wanna be TRULY shocked by a statistic?
    Check this out, under the FUEL section, bottom left….
    I recently worked out that my van had been through 54,000 litres of diesel (666 tanks of fuel) when it passed its 300,000th milestone The first of those litres would have cost 77p the most recent around Β£150, so that vaguely averages to Β£54k. Thats 144 tons of CO2 which is about 80,000m3 which is approximately the volume of the Albert Hall.

    How many Wales’s is that?

    monogramman
    Member

    I’m currently averaging 16mpg! Don’t know how good you have it you lot πŸ˜€

    Premier Icon maccruiskeen
    Subscriber

    How many Wales’s is that?

    exactly one Wales, if you spread the Co2 0.00385mm thick

    PeterPoddy
    Member

    I recently worked out that my van had been through 54,000 litres of diesel (666 tanks of fuel) when it passed its 300,000th milestone The first of those litres would have cost 77p the most recent around Β£150, so that vaguely averages to Β£54k. Thats 144 tons of CO2 which is about 80,000m3 which is approximately the volume of the Albert Hall.

    Lovely. GEEK TO THE MAXXXXXXXXX! πŸ˜‰

    davidjones15
    Member

    How many Wales’s is that?

    Oi! πŸ‘Ώ

    boblo
    Member

    That 2l Omega lump did quite well on fuel compared to your much newer Focus (1.6l IIRC). Shows how crap the Focus (and many other newer cars) is really.

    Premier Icon molgrips
    Subscriber

    Shows how crap the Focus (and many other newer cars) is really

    Not really. The type of drive varies which skews the averages and the Focus still comes out ahead.

    boblo
    Member

    Moly, you must be very clever to extract that conclusion from the data shown…

    However, yes it comes out ahead. But, a knackered old lump (PP in this case πŸ™‚ ) in an old auto Omega is only ~4mpg better than a much newer, manual 1.6l Focus?

    You’d have thunk the gap would be biggerer no?

    Premier Icon maccruiskeen
    Subscriber

    You’d have thunk the gap would be biggerer no?

    cars keep getting heavier though so older cars perform better than you’d imagine for their older tech, the new ones are are pulling more weight around. I think the current fiesta is double the weight of the first ones.

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