It’s well documented that Ian is obsessed with fuel consumption and I fear he’s got me hooked as well:)
The Mondeo has been acting strangely and neither of us can come up with a reason why it happens.
The first time was on our trip to Cornwall in June with the caravan on the back.
Obviously the fuel consumption read out dropped, and then settled, at around 29mpg after an hour’s drive.
We stopped at Sedgemoor and as soon as we pulled out again it started to drop consistently all the way to Cornwall reaching 26MPG by the time we got there and was able to drop the van off.
On the journey home it settled at around 28.4mpg and stayed there.
With normal use back home we were delighted to get to 50.7MPG where previously the best we could manage was 48.6 MPG.
On a trip to France a couple of weeks ago (without the van) the same thing happened and it dipped to 47.9 for no apparent reason, but returned to 50.6MPG back home again.
Last weekend we had to go to Scarborough and decided to go the pretty way via Lincoln, Humber Bridge and Beverley and return via M62, M18 and the A1.
Sure enough, around an hour into the journey up there, the fuel consumption started to drop slowly and finally settled at 48.2 on the journey home where it is now.
The amounts are certainly not critical but nevertheless, extremely annoying as neither of us understands why it happens whenever the car is not doing local, short journeys.
Surely the fuel consumption should be better on a long motorway journey?
On every occasion there has been no obvious reason such as a head wind, change of driver or filling the tank up with a different brand of fuel.
So, I throw this open to the technical minded ones on here to solve the conundrum because the best we can come up with is that the Mondeo must get homesick!
Pat
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I wonder whether your car has a DPF that regenerates on the longer journeys Pat? Would that use more fuel? Seems strange its every time though... If I was driving it'd probably just be a result of me (unconsciously) speeding up towards the end of longer journeys to get it over with!!
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It does have a DPF Peter, or so I understand and I have googled this before posting here.
I found that it shouldn't make any difference to the MPG though as it is only a small initial burst of fuel...or something like that!
Perversely, I drive it fast and furious and Ian drives fuel efficiently...I always drive locally:)
Pat
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Perhaps it's just because everywhere is uphill from where you live then! More efficient coming home as you're then going back down ;-)
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The road to Cornwall is quite hilly and twisty, lots of braking and acceleration. I suggest that is why you are getting higher fuel consumption.
The last time I drove to Cornwall I made the mistake of leaving the cruise control engaged, that resulted in poorer consumption, as the car was being braked on the descents and floored on the uphill bits.
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>> It does have a DPF Peter, or so I understand and I have googled this
>> before posting here.
>>
>> I found that it shouldn't make any difference to the MPG though as it is
>> only a small initial burst of fuel...or something like that!
>>
>> Perversely, I drive it fast and furious and Ian drives fuel efficiently...I always drive locally:)
>>
>> Pat
>>
>>
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DPF regen has significant fuel economy impact on the Insignia; imagine it's the same on your Mondeo. Ruined my last hyper-mileing attempt.
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I presume the MPGs are all instant readouts from the computer? Did it only vary significantly on the trips you mention Pat, or it it an ongoing issue?
If so, it could be the computer, rather than the car, that's misbehaving. Ian can check this easily by keeping a note how much diesel he buys and the mileage at each refill. I'm not suggesting you do it - it seems he enjoys that sort of thing :-)
I had a 3 series with an analogue mpg readout that used to swing wildly between infinite (now there's a selling point!) to < 10 mpg but comparing the service station receipts showed it was doing a steady 28-29 mpg.
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>> I presume the MPGs are all instant readouts from the computer?
Instantaneous fuel consumptions go up and down like a yo-yo, and hence have no value. Well, that's my experience with all the cars I've had which had trip computers. If I take my foot off the reading goes up to a maximum of 99.9 mpg which is meaningless. A friend had a British Leyland something or other which gave readings in the hundreds of mpg when the accelerator was released which was even more meaningless.
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>> Instantaneous fuel consumptions go up and down like a yo-yo, and hence have no value.
..unless you want to know your instantaneous fuel consumption presumably? It's only doing what it says on the tin :)
>> If I take my foot off the reading goes up to a maximum of 99.9 mpg
>> which is meaningless.
It does require you to insert 'at least' into your interpretation, so it's more imprecise than other readings, but I wouldn't class it as meaningless, unless you are talking about average consumption (which isn't what it's for).
>> A friend had a British Leyland something or other which gave readings
>> in the hundreds of mpg when the accelerator was released which was even more meaningless.
Surely less imprecise, given that presumably it could give readings up to 999.9mpg before he needed to insert the 'at least'?
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It is the average fuel consumption read out and it only ever varies on the long trips we do which really are few and far between.
Lygonos, I always have a window open (smoking!) and that's why I don't like flying!
It's not traffic related as the trip to Scarborough at the weekend was all stop start going and we sailed home early on Sunday morning on cruise all the way.
I will get Ian to do another check but he is beginning to complain that he enjoys doing it at work as he gets paid a fuel bonus every three months and only gets grief from me in the car!
Pat
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Windows up vs windows down (eg having a fag?)
AC on vs AC off.
Following a mimser.
Using cruise control.
Overtaking.
Sitting behind a lorry.
etc etc
So many factors involved including invisibles such as prevailing wind direction can all influence consumption by 5-10% so your variabilities appear well within normal distribution.
If DPF regen uses around 0.1 litres of fuel per pop (can't find a definitive amount on t'interweb) = perhaps the equivalent of 1 mile worth of diseasel, thus would 'cost' about 1mpg over a 50 mile test. I wouldn't have thought a regen would be necessary more than about once per tank though - no doubt a real engineer can correct this assumption!
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Pat, I assume you're looking at the average fuel consumption reading on your trip computer. It sounds to me like it's defective. Just out of curiosity, over what distance does it calculate the average? Incidentally, I treat trip computers as being toys which are not to be taken too seriously.
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Air temperature change ?
This and tyre pressures seem to have an effect on Diesel fuel economy, or so I have found out.
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>> Incidentally, I treat trip computers as being toys which are not
>> to be taken too seriously.
The trip computer in my BMW is optimistic by 6%. It's consistent, which means it is perfectly useable as a measure of fuel consumption.
It's no more a toy than the speedometer or fuel gauge, neither of which manage better accuracy than that.
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>> The trip computer in my BMW is optimistic by 6%.
How did you arrive at that figure? What was your method of calculating the consumption?
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Brim to brim calculation over the first 4000 or so miles. After which I got bored.
Miles on trip / litres added to second click *4.55
Last edited by: DP on Thu 19 Sep 13 at 09:40
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I keep a log of fuel and miles and as I always fill the tank it's a reasonably accurate method of calculating consumption.
The trip computer varies by up to 10% either way against my calculations.
An old motorist taught me the trick of keeping a log of fuel and miles as, in his experience, a fault never caused a car to use less fuel. It's certainly indicated a few problems before they've become serious.
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>> An old motorist taught me the trick of keeping a log of fuel and miles
>> as, in his experience, a fault never caused a car to use less fuel. It's
>> certainly indicated a few problems before they've become serious.
>>
An unusual noise is also a good indicator of a problem, usually the longer you leave it the more it costs to fix.
Last edited by: Old Navy on Thu 19 Sep 13 at 10:21
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The idea of DPF regeneration is a good one.
I think DPF regeneration is triggered by the output from a differential pressure sensor on these, so, if the DPF is becoming blocked, the car will go onto frequent regen cycles when the other necessary conditions are met, i.e., the engine being up to temperature, and speed is sufficiently high for a period of time.
So, a blocking or blocked DPF is a possibility, as is a problem with the differential pressure sensing. To check this, needs live data on the differential pressure sensor output while motoring.
Has low ash oil been used?
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>>Has low ash oil been used?
ie. does the engine oil spec have a "C" rating amongst the Ax/Bx bit.
Plenty of 'turbo-diesel' oils do not have a low ash rating, and they do not specifically advise against using in DPF equipped cars on the packaging (Mobil-1 0W-40 for one)
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Non "C" rated oil in a turbo diesel (DPF or not) can also cause EGR valve fouling. Not good for fuel consumption either.
Last edited by: Old Navy on Thu 19 Sep 13 at 10:42
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The car I have now is the first with a MPG readout. It only shows average consumption from a manual reset - no instantaneous readout. I generally fill to brim beginning of month and top up as required through the month and note the total mileage covered and what it has taken to fill back to full and the end of the month. I compare the readout with a manually calculated version. It always comes out at less than 1% difference MPG readout showing higher. This is a consistent month on month figure which I deem to be reliable enough for me.
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Firstly, the variations you are looking at are fairly small anyway, so even if they were for apparently identical journeys the random variation would probably be on that scale.
Secondly - what are you actually reading? Do you keep resetting, or is it some sort of rolling average? Rolling averages (e.g. the average for the last 100 miles at any point) do odd things, because any change you see depends not just on the data points you have just added, but also on the ones that have just been dropped.
My fuel economy is all over the shop. My computer left to its own devices will auto reset whenever it the engine has been stopped for four hours or more. So for most journeys I get a fresh start (I can switch to manual reset which I have never reset, and so gives me a cumulative figure from new). Three consecutive overtakes on the way back from Cambridge yesterday (I had been there less than four hours so the average was for about 90 miles at the time) dropped the mpg by a whole mpg.
Speed of course makes a big difference owing to air resistance increasing by the square of the speed. With caravan this is really marked and at a true 60 on a motorway I get about 26, dropping back to lorry speed increases this to about 30.
Traffic speed makes a big difference. On a slow A road behind a lorry, leaving a big gap and smoothing out the speed variations I get great economy. Acceleration costs fuel, so speeding up and slowing down a lot is bad - I always struggle through Milton Keynes because of slowing down every half mile for a roundabout, even when I avoid stopping. Wind ditto. You would hardly notice a 5mph wind but if that moves from behind to in front it will make a material difference.
But to make any sense of this I'd want to kow what you are measuring.
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To be honest Pat I think that your variations of 26/28.4/29 and 47.9/48.2/50.6 are in line with what I'd expect due to differing route and driving dynamics.
Your non-van figures are similar to both my current Alfa and the C5 before it except the C5 was exceptional on a long modest speed run getting nearer 56mpg.
I did one tank to tank with the Alfa to judge the computer reading and since then have used the computer.
Mine has an average that you have to manually reset in the menus which I've not done since I bought the car... so the figure hardly alters because it is already a long term figure.
It also has a "B" menu with all the same figures but for the latest journey. This auto resets so as you take a new trip the next day you can compare the long term to the current day. That seems to accurately reflect driving and route types so I'm happy to trust and quote it.
Last edited by: Fenlander on Thu 19 Sep 13 at 11:34
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The average is just that and we only manually reset it when we hook the caravan on (and off).
I knew this one would be difficult to explain!
Take the journey to Cornwall as an example: Manual reset leaving home and average MPG had settled by an hour into the journey.
Two hours later we stop at Sedgemoor and when we pulled out it dropped slowly all the way to Looe for the next 3.5 hours.
It was just the same at the weekend when the figure was steady for the first hour or so then suddenly continued to drop slowly for the rest of the weekend.
It hasn't been used since so I don't know what is happening.
I'm sorry but you've lost me with oil as it goes back to the Ford dealer for servicing and never needs a top up between services at all.
I think at the back of our minds is that it may be an indication of something wrong and I think it was NC (Grrrr, I wish I could see all the posts while posting) hit the nail on the head and voiced our worries.
Pat
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>> (Grrrr, I wish I could see
>> all the posts while posting)
Click the wheel on your mouse on "reply to this message" and it should open in a new tab. You can then flip between tabs to see your reply and the complete thread. Just a thought.
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What a brilliant idea crankcase, why ever didn't you tell me that before?
Men tut!
Pat
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Re the DPF thing my C5 would do it and the instant reading would fall massively but the average was hardly affected unless you were only taking the average over a short distance.
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>> Surely the fuel consumption should be better on a long motorway journey?
>>
Completely different car, but my daughter commented that the trip computer MPG had fallen off a cliff in her Mitsubishi Colt (it's a 1.1L 3cyl petrol).
It normally will nudge 50MPG even on urban journeys but was suddenly doing 40MPG. This co-incided with a change in job and she now does a 15 mile motorway run to work. After much investigation we've concluded that the car just doesn't like doing 70MPH!
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My fuel consumption suffers when SWMBO drives. It doesn't go down too well when I suggest slower uses less, as would use of the two upper gears.
Perhaps your daughter drives like my SWMBO BP?
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My Jazz has an instant mpg readout but I still log miles and fuel. It reads about 9% optimistic.
Hills = bad news- even if the downhill = uphill and you coast you can never recover the extra fuel due to speed limits and traffic and other fings. And above 60mph, fuel consumption rises quickly - hardly surprising.
Stop/start driving murders consumption even if engine is warm.
I have learned to drive with a light right foot but if I press on or am careless can increase consumption by up to 15%.. As for driving up a hill from cold and accelerating uphill, increase consumption by 25% +
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Edit
Consumption over 4k miles (effectively from new):
stop/start 37-40 mpg
A roads: 52-57 mpg
Motorways : 54mpg (approx)
Average YTD 42mpg. Mostly urban driving.
Average last 1500 miles : 45mpg (summer and run in?
Worst seen: 35mpg: in snow and ice
All adjusted down by 9% (see start) to be "real".
Last edited by: madf on Thu 19 Sep 13 at 12:41
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>>>My fuel consumption suffers when SWMBO drives
Same here... not being unkind it's just a fact. And she overheats the brakes.
She's been using the Alfa most days for the past few weeks and the clues are there... like the contents of the centre console thrown out into the footwells and the parking money in the open centre console ashtray g-forced into the impossible to reach area down round the seat sliders.
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Fuel consumption must be the only form of motoring OCD that I don't have, as long as my car is doing roughly 125 miles per quarter tank it is about right. :-)
Last edited by: Old Navy on Thu 19 Sep 13 at 16:07
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>> My fuel consumption suffers when SWMBO drives. It doesn't go down too well when I
>> suggest slower uses less, as would use of the two upper gears.
>>
>> Perhaps your daughter drives like my SWMBO BP?
>>
No, but my wife does! She'll accelerate nicely away from lights and then at the point where the next thing to do is change to 4th, she'll stop accelerating and just keep going in 3rd!
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That used to happen in our Panda.
Now we have an auto, it is bliss not to be grinding teeth and biting tongue as too low a gear is held while SWMBO chatters on!
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Fuel Consumption Conundrum - PeterS
