I've averaged about 35 mpg in my diesel Avensis over the last 3,500 miles (6,500 to 10,000). I thought it must be my style of driving - heavyish right foot - and so I tried to baby it along: gentle acceleration, smooth driving, hardly any above 70 mph.
Result: 43 mpg, brim-to-brim. Which is crepe.
So I filled up with Shell V-Power. (Not sure it made any difference to anything.)
Pootling at an indicated 70 (slightly over 66 mph according to the computer) on the M6 Saturday afternoon, and using the computer (I know, I know) I seemed to be getting about the same 40-ish mpg. I reset it and it dipped to around 30 mpg (still at "70").
I remembered reading something here about regularly pushing the revs to 4500, so I did that for maybe a mile (perhaps less), about 50 miles from home. I then kept a steady "70", for the next 50 miles (mix of A66 and A1(M)) and got just over 51 mpg (again, according to the trip computer).
It seems a remarkable result. I presume the 4,500 rev thing blasts out the pipes (I hope I'm doing no damage) and I propose to repeat this for the rest of the current tankful, and for the next.
Anyone else had this experience?
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What's happening is that you've reset the computer awau from your normal heavy-footed to-and fro and discovered the better economy you normslly get on a constant speed cruise.
There's no secret to it (certainly not 'trick' fuels, which, because they cost more, and anything but cost-effective) other than a properly maintained car driven well at consistent speeds. Flog it if you want to, but you'll pay.>> I've averaged about 35 mpg in my diesel Avensis over the last 3 500 miles
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Not sure you give a good breakdown of what is motorway, good A road and around town for the miles.
Also how many MPG are you expecting? Not the manufacturer's figures surely???
On mostly motorway runs with little stop-start (but some) my Mazda6 gives about 44mpg now (getting better as the engine loosens.... around 8k so far). Around town it is a lot worse and so was the previous Mondeo TDCi and the Passat 1.8T Sport.
Am I unhappy? No. Average pence/mile around 11-12p which is excellent considering the cost of fuel!
But I used Shell V-Power by mistake (started filling and thought what the heck) and also Sainsbury's and I might have got a few more MPG. I normally use Tesco. But for the extra hastle and loss of Clubcard points I'll continue using Tesco for now. And my lease company/employer encourages use of supermarket fuel anyway.
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I'd be devastated by those figures - my MB C270CDi estate auto will do low 50's on a long enough steady run.
Today I went up the M6 and across the M65 to Colne - drove low 70's and pretty well uphill all the way, but of course downhill on the way back (although the car never quite seems to gain as much downhill as it loses up hill). 168 mile round trip and 49.6MPG on the trip computer (had been 50 at one point).
I do try to make a point of opening it up every now and then, but you're supposed to do it under load and my car just takes off if I floor it and I wouldn't keep my licence long. If I run in a lower gear then that's not really under load.
Edited by Bill Payer on 31/03/2008 at 21:44
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Don't remember my 2000 avensis non d4d being quite so heavy on fuel, but there was a very distinct difference when taking it steady obviously.
I too think your cars do seem heavy on the juice, SWMBO gets a constant 30 (computer ignored) out of her 3 litre hilux, a 2 ton brick, and she deffo don't take it steady, and thats all shortish running round.
Why are the new shape avensis so heavy on fuel.
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I have a new shape diesel avensis. Mixed use, urban/rural/motorway, averaging 51mpg over the last 11000 miles.
If anyone's is doing 35mpg there is something wrong, either with the car or the driving style.
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"49.6MPG on the trip computer"
MB trips computer might be accurate but all others in my experience are not.
My example of around 44mpg included some town driving, some heavy acceleration on the motorway when need to avoid the numpties and it's still loosening up. Oh and some town driving including being stationary whilst I let Sarcozy and his wife pass last week near old Windsor ;-)
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My experience with a Mazda 6 diesel over 3yrs was 44 mpg yet the computer always indicated approx 49 mpg.
A Mondeo and a BMW belonging to friends both have optimistic trip computers. Reading this thread makes me query the value of these devices.
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After 52000 miles my 1.9Tdi Audi auto has given me around an overall 43-45 mpg (Brim to brim calculations - not the rubbish computer which lies by about 10%). I guess 60% - 70%is on motorways at about an indicated 75-90 mph (depending on country). Sometimes I've had everything and the the kitchen sink on the roof bars too (driven slower then!), the remainder is stop-start driving in town.
I'm happy enough.
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I've got a 57 reg 5k miles) D4D Avensis and even with my hevay right foot never get less than 45mpg - usually sits at 47.something.
I have found that using 6th gear to climb a hill is not a good idea though - it drinks the diesel faster than a Sierra Cosworth drinks petrol!
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Mine's a 55 reg i-CTDi Accord with 62k miles. Mixed motoring with little town and probably 70% motorway has seen an overall average of 41 mpg. Bikes on the roof drops that to about 37 on a single tank. Fancy fuel can bring it up to about 43 at best, have never seen better than that.
Strangely, the third tank I ever put in I got 54 mpg brim to brim. I've never been anywhere near that again.
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This topic is a regular - just do a forum search. From all the contributions various points emerge:
- cars' computers are probably accurate to about 10%. They will be useful as a guide to whether you are driving more or less economically today, but if you want to know your car's true consumption, record your fuel purchases and distance travelled over 1000 miles or more. Trading Standards make sure that fuel is dispensed accurately, and your car will measure miles travelled, usually overestimating by 1 to 3%. You can allow for this if you calibrate it against the motorway markers or use GPS.
- some people's diesels give consumption figures so poor that their engine's systems must be either misadjusted or clogged. HJ advises us to use conditioner occasionally to clear the injectors (or you can buy super-diesel at some stations which do it). You may find that a new air filter works wonders, but a newish car shouldn't need that. My own car's consumption started to deteriorate despite doing this and needed the timing adjusted, which cleaned up the exhaust too. It is also true that a good blast helps from time to time. But I would guess that a car with lousy consumption (<45 mpg IMO) won't pass the MoT emissions test?
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not the rubbish computer which lies by about 10%.
In this and other similar posts I note a general consensus that trip computers are inaccurate as far as mpg are concerned. Can someone explain in simple terms how these thing work - where do they get the fuel consumed amount from and why are they are inherently inaccurate ?
Edited by CGNorwich on 01/04/2008 at 11:58
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The computing part of the computer will be more than adequately accurate. It's the input data it is working with that are a litle suspect.
The engine management unit may report what the injection duration is, and how often injection pulses are happening, but the engine management unit does not actually know how much fuel is actually being injected. The amount is calculated, and as far as the engine goes, small corrections are made via the mechanism of the lambda probe in the exhaust.
The trip computer relies upon summing up all of these injection events, so even a tiny error in the assumptions which are used to calculate fuel usage from injector pulses will accumulate.
The same cumulative error will come from the vehicle speed sensor. Usually, this is done by counting wheel revolutions. There are at least two obvious systematic errors here. First, the wheel rolling radius changes as tyres wear, and second, the peripheral speed of the wheel, and the road speed are only the same if the wheel is not experiencing any tractive or braking forces. For the wheel to generate any force, it must slip a little.
The best use for a mpg estimation from these computers is the instantaneous reading. Don't believe the absolute value it tells you, but use the relative numbers to help guide you towards efficient habits.
Usually, an averaged value is more representative than an instantaneous one - but, in this case, where the errors are systematic rather than random, that isn't the case.
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I have found on the trip computer in my Saab that it gets closer to accurate if you let it run on for large distances, the last couple of times I have let it run more than 1000 miles between resets it was within 0.5 mpg of the measured figure.
Given that I don't know how accurate the mileometer is that's about as close as I'm going to get I reckon.
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Thanks Number_Cruncher - most informative
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I suspect that when a car is not moving, the trip computer stops calculating mpg, i.e. the fuel used to keep the engine idling does not count in the running average. A town run is therefore less accurate than a motorway run.
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I suspect that when a car is not moving the trip computer stops calculating mpg
Mine doesn't stop. I watch the average mpg reduce at traffic lights.
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Which engine do you have? With the D-4D 180 engine this seems to be a well known problem. Go to the Toyota forum: toyotaownersclub.com/forums/index.php? and look in the RAV4 and Corolla Verso sections as well as the Avensis area. There are quite a few threads on this topic.
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Thanks all.
Must be the DPF, I suppose.
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i can't buy into that
i have the t180 in an auris
i just drove for econonomy on a trip computer reset on a round trip from work yesterday. I got 47.3mpg
I got 53mpg on the same test last summer when the whether was better.
Avg even with a very heavy right foot is 43mpg. 45.4mpg being the official combined figure.
I can't believe these cars only get 35mpg and 41mpg at best. Infact i drove an avensis last weekend for a day a 2.0d4d. I reset the trip computer and got 47mpg for the day. 44mpg when pushed. Brand new as well.
I even get 41mpg out of our 2.2d rav4 which is also a year old. Can get more on a long run and thats a big, heavy car.
You sure your not pressing the accelerator down too much? You know you can sit at the same speed with very little pressure on the accelerator. Always make sure you dont labour the engine and keep the revs around the max torque range. Also its best to accelerate quick quickly up to speed then come off and lightly apply enough pressure to maintain speed. Also come off throttle much earlier before stopping reducing the amount of braking you do.
You carrying any extra weight, constantly use air con and checked your tyre pressure?
Edited by OldSkoOL on 03/04/2008 at 00:48
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To quote an old petrol advert "Decoke Daily While You Drive" (but do watch out for the cameras as the "Speed Limit Ends" sign doesn't mean that anymore)
A colleague quite a bit older than me said that during the war he was on bombers. They would cruise the engines gently except for a minute or two every quarter of an hour during which time they would thrash the engines really hard. When this was done loads of burning carbon would be ejected from the exhaust pipes. Allegedly if this was not done the engines would clog-up and be no use when full power was needed. This decoke method is still a good technique today. For example my "new" Rover 800Di was a huge disappointment at first, being roughly 30mph slower than the Rover 825SD that it replaced. (Admittedly the 825SD would cause whinging at the MOT when they stamped the accelerator to the floorboards and made black smoke. I would say "What do you expect? I don't drive like that, there's no black smoke when I'm driving!" ) Anyhow after a couple of Mr McGoos had run into it, it was time for a fresh car. A Rover 800Di drive-by-wire machine was bought and initially was a huge disappointment - so slow, but impeccable on the MOT smoke test as the computer just will not allow black smoke. "There's nothing for the machine to measure!" they said. After a couple of long hard thrashes up-country the speed has come up by about 30 or 40 mph! absolutely amazing! There must have been a lot of coke in the engine. Mpg is now better too, although strictly speaking decoking your engine this way is illegal unless you live in Germany. Note that just revving the engine hard will not give the decarbonising effect, it is the HEAT caused by using maximum power for a while that gets rid of the carbon. Towing a trailer uphill will give more heat, but the autobahn method is still the best.
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And things have gone full circle, the approach you describe of getting heat into the exhaust system is what's needed with the latest- generation coated DPFs.
If the DPF matrix doesn't get heated to around 350 - 400 centigrade for a long enough period, it will not start "cokeing" the soot build-up to regenerate, and will slowly clog up.
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Interesting cos I've been disappointed recently by the mpg from my 320d - 40-42 indicated (really 38-40); see earlier posts. Last summer I was getting 45-48 mpg (indicated) on the same usage/driving style. Maybe the lower ambient temperatures are a factor. Maybe it's 'soot' bringing down efficiency.
I'm on my 2nd tank of V-Power. Probably my last...
Edited by Mad Maxy on 03/04/2008 at 20:03
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Most fuels suffer in winter; diesel more than petrol
- diesels take longer to warm up and this time to warm up is increased in winter
- so... when fuel is cold it doesnt generate enough heat (power) so more fuel is required to get the same power
- at this point the engine is running less efficiently, more fuel is required for combustion mixture which includes air
- cool dense air common in winter months and since dense air is heavier more fuel can be pulled in which maybe good for performance but bad for economy.
- and finally the last possible reason consumption drops is cool dense air being heavier can effect the areodynamics of the car as it travels by increasing resistance which in turn requires more fuel to achieve the same power
dont forget even now its still around 8-10 degress cooler than the avg. summer temperature. Or half as warm.
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I bought a 53 Reg 2.0 Diesel Tourer last year with 70k and full Toyota service history.
The engine has been run in longer than your own but in the 15 months that I have had the car it has averaged between 51 and 52 mpg (mainly motorway driving).
I found that the computer told porkies when it came to consumption. One one run, I got 680 miles from the tank anf filled up to the brim. With what was left before filling up I calculated that I had done about 58mpg but the computer indicated 68mpg.
Please note that the computer needs resetting once you have put a new set of tyres on, obviously the previous owner didn't. After resetting the computer to allow for a recent renewal of tyres it still overestimates the amount of miles that I get to the gallon but by a lesser degree.
I too have recently used Shell V-Power but have yet to be convinced that I am buying a superior fuel to normal Shell diesel.
Regards
Paul
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Please note that the computer needs resetting once you have put a new set of tyres on
Sorry- you mean it adjusts itself somehow to take into account the tyre size?
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If you go to the Avensis forum over on the toyotaownersclub website you will see endless posts from people complaining of poor MPG from their diesels. Same on most of the other Toyota model forums also.
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I have a d4d Avensis 2.2 with around 15000 on the clock. General knocking about town and commuting locally I get around 45mpg but I rarely get stuck in any real traffic. On a recent trip to Cornwall, we live in Essex, I got 48mpg on the trip down there with some local running around. This was from brim to brim, the computer showed 46. The trip back returned 53 according to the computer, I haven't refilled yet but expect around 54-55 in reality. I get this level of economy regularly on runs but do keep my speed to around 70 on my sat nav (about 75 on the speedo) and only use cruise control on clear roads.
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I've seen threads like this from owners of Mondeos, Primeras, Accords, 6s, Lagunas and Avensises. All point to the same thing -- mid-40s mpg if you're lucky from mid-size diesel hatchbacks.
This is astounding -- I get high-30s mpg from my petrol Primera overall, and with the difference in fuel costs per litre this means that it isn't costing me massively more than it would be from one of the above cars potentially.
Can't see the point in these diesels if I'm honest, based on these reports.
The other thing I've been wondering, related to the computer readouts, is this: if MPG is 10% too high, and MPH typically reads around 10% too high in the same way, does this mean that a 100,000 mile car has only really done 90,000 miles?
And if so, can I justifiably take my car in to be serviced 1000 miles late and claim its down to odo inaccuracy?
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