How much more diesel does an automatic gearbox use vs. a manual ... on motorway driving?

Hi

Like for like, does having an automatic gearbox use more diesel ON THE MOTORWAY? And if so, what %age more?

Background
I think have recently managed to write-off my top-of-the-range 2007 Honda Accord 2.2 Litre manual diesel that I have been driving for the last year, during a recent traffic accident. I do a LOT of long distance motorway driving and even following a remap, I was getting was doing about 550 miles on a tank (with the on-board computer claiming a slightly optimistic 50-60MPG depending on speed/head-winds etc). My temporary little hire car has an automatic gearbox and I have to say it is SO much more easy to driven when in towns. Also my girlfriend doesnt have a manual just an automatic driving licence! Clearly one problem with automatics is that they tend to rev far too highly and thus use a lot more fuel. But my question is: given that I do about 85% of my driving on motorways, how much more fuel I am I likely to use in practice?

J

Hi John,

I'd estimate around 5% more, so if the manual did 50mpg, the auto would be 47.5mpg for example.

The auto is a 5 speed with paddles on the steering wheel, so best of both worlds really.

Just the auto gearbox oil change due at 67500 miles, but thats only £150 or so.

As you say, great in towns.

Rich

Two reasons why conventional automatics (fluid clutch) give worse mpg than a manual (dry clutch)
1. the gearboxes are different and have less gears, so the engine has to work over a wider rev range than it would with a careful driver using a manual gearbox
2. "clutch slip" loses energy, the driving member of the clutch spins a bit faster than the driven member, even on cruise. With modern torque-lock, this is overcome in cruise, but as soon as you change your speed, it's likely to drop out of torque-lock.

I have a 2009 (8th gen) honda accord idtec auto box diesel, have had for just over a year now and use it mainly on long trips (due to dpf). I had a manual diesel skoda superb previously and used to get 50 plus mpg from a 2.5 V6 engine..... but the accord gives a significant drop in returns on fuel. I find that I usually get 41 to 43 mpg on motorway long trips. There have been the odd occasion when i have got 45 plus but usually when speed has been kept below 70mph. But having said that, this is my first automatic car and the benefits in purely driving without gear changing and the benefit of constantly having both hands on the wheel and added concentration you have is worth the loss of mpg return. I would also add that if you switch to S mode and use the paddles to change gear you will again get a significant drop in mpg... usuall high 30's .... hope this helps.

If I was you - Steer clear of the Honda Auto Box.

Ive had mine over 2 years, its only ever managed 41-43 mpg on motorway and in down 30-33. When cold its like a cement mixer and has a terrible gear shift.

IMO this gearbox is like retro technology - its clunky, slow and swallows up all that lovely torque. Get a manual if buying a Honda!!!!!

amialrightover said:

I have a 2009 (8th gen) honda accord idtec auto box diesel, have had for just over a year now and use it mainly on long trips (due to dpf). I had a manual diesel skoda superb previously and used to get 50 plus mpg from a 2.5 V6 engine..... but the accord gives a significant drop in returns on fuel. I find that I usually get 41 to 43 mpg on motorway long trips. There have been the odd occasion when i have got 45 plus but usually when speed has been kept below 70mph. But having said that, this is my first automatic car and the benefits in purely driving without gear changing and the benefit of constantly having both hands on the wheel and added concentration you have is worth the loss of mpg return. I would also add that if you switch to S mode and use the paddles to change gear you will again get a significant drop in mpg... usuall high 30's .... hope this helps.

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Agreed the benefit of being able to fully concentrate on steering is great, also its so controllable from your right foot, you can get it to change up or down as you want. Also if you want to race the paddles can change faster than any human can.

Was also good in the snow, no problems.

Auto is the future, why do we still have manual boxes, they have been around for almost 100 years.

Autos don't work for everyone, you need to have empathy with the car,be able to become one with it and feel the gear change points on the throttle. Violent people with no light touch cant get on with them. Kind of people who are clumsy and stomp around etc.

I drive both and prefer auto's but each to their own

> Auto is the future, why do we still have manual boxes, they have been around for almost 100 years.

I'm no expert, Richsprint, but the answer appears to be in the thread above.
i.e. The fuel consumption appears to be truly, utterly appalling.

For example Amialrightover is only getting "41 to 43 MPG" and only gets up to 45MPG if he goes below 70MPG, whereas on my 2007 manual 2.2L i-CDTI with 120K on the clock I was doing well over 50MPG.

I had no idea that automatics are still so inefficient. "Clutch slip" even during a steady cruise? What the HECK is going on? I'm tempted to suggest that these kind of gearboxes should be made illegal. Awful, awful, awful.

Honestly the entire car clutch mechanism need to be re-invented. Even on manual cars they are a dreadful design, with the entire torque going through two plates simply pushed hard together... which then of course wear out, start slipping and need to be replaced at vast cost. Bl**dy useless. We put a man on the moon 40 years ago, but we cant build a clutch that doesnt either wear out OR which guzzles fuel by slipping all the time. WTF!

Now, OK, if it's only 5% extra fuel, then maybe I could justabout live with that. But from the above it sounds more like and extra 20 to 25%! What am I missing - perhaps the new Honda diesel also much less efficient than the i-CDTI??

J

ship69 said:

I had no idea that automatics are still so inefficient. "Clutch slip" even during a steady cruise? What the HECK is going on? I'm tempted to suggest that these kind of gearboxes should be made illegal. Awful, awful, awful.

Honestly the entire car clutch mechanism need to be re-invented. Even on manual cars they are a dreadful design, with the entire torque going through two plates simply pushed hard together... which then of course wear out, start slipping and need to be replaced at vast cost. Bl**dy useless. We put a man on the moon 40 years ago, but we cant build a clutch that doesnt either wear out OR which guzzles fuel by slipping all the time. WTF!

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Generally speaking, it's only on auto-gearboxes up to the 90's that you won't find torque-lock (a few did before then, some might do even today). Without torqu-lock an auto-gerbox is ineffecient. A clutch in a modern auto-gearbox is now referred to as a Torque Converter. Even so, they are not as efficient as a dry clutch.

But there is the dry dual-clutch as used in some true "flappy-paddle" semi- and full-automatic sports cars (and I guess that F1 clutches work in this manner)

But otherwise, there isn't much else, and at the end of the day, a car is a very primitive device. 50 years from now when everyone is driving something that has electric motors in each wheel, with fuel-cells (or similar) to provide the electric power, they will look on the cars we now drive in the same way we look upon steam engines.

It's not the first time that the iDTEC has been compared unfavourably to the i-CTDi regarding MPG, I think it's the DPF?

Torque converters are ineffecient under heavy load and do get quite warm - not sure about Accords, but my old 2.8i Mk2 Granada had a radiator for the autobox.

Clutch plates do wear out, but then so do brakes and tyres!

> It's not the first time that the iDTEC has been compared unfavourably to the i-CTDi regarding MPG, I think it's the DPF?

How strange. OK I'm trying to do a like-for-like and according to Parkers comparing manual cars:
"Tourer 2.2 i-CTDi EX 5d" does 47mpg (9.1 secs 0-60, 122mph top speed, 138bhp), whereas
"Tourer 2.2 i-DTEC EX 5d" does 50mpg and is faster (129mph, 147bhp, although has a slower 0.6 time of 9.8 secs)

Links:
http://www.parkers.co.uk/cars/reviews/facts-and-figures/honda/accord/tourer-2003/34292/
http://www.parkers.co.uk/cars/reviews/facts-and-figures/honda/accord/tourer-2008/40208/

So is Honda/Parkers essentially *lying* about the mpg (and power) improving? (Or is it something to do with user maintenance/correct oils etc?)


Fwiw, interestingly there is also a
"Tourer 2.2 i-DTEC TYPE-S 5d" which also claims to be better MPG than the i-DETC's mpg
It does 49MPG, AND is also faster again: 177 bhp, 135mph, 8.5 secs 0-60.

I am intrigued but the latter because last time around I bought a "Tourer 2.2 i-CTDi EX 5d" (which I unfortunately managed to recently crash and write-off) and after I got it re-mapped the clutch immediately started to slip quite badly so I spent a fortune on a new racing clutch which to be honest was a nightmare in towns juddering quite badly from time to time. All in all it might be better to buy a car that is designed to handle the higher torque and save hassle on clutches!

Having tolerated my lumpy racing clutch for so long I'm still itching to get an auto gear box (/Torque Converter) even if if I do sacrifice a few mpg... however if the best 0-60 time ends up being over 10secs, I might be forced to think again. I mean 10+ secs for 0-60? That's almost dangerous! ;^)

J

If Id got the cash Id get a type-S just for the clear indicators. A remapped Manual idtec @ 190bhp 0-60 = 8.2 secs

Motorway/urban = 56 mpg
B roads and urban =49-50mpg



Ive had an auto Celica and loved it. If it didn't under steer so bad it would have been my favorite car that Id owned. Though I was getting 22mpg.

Racy Jace - Yup Those stats sound good. But I'm confused... is that a screenshot of the dashboard or what?

Even without a remap according to Parkers the stats for a Type S are pretty good:
49 mpg, 177 bhp, 0-60 8.5 secs

http://www.parkers.co.uk/cars/reviews/facts-and-figures/honda/accord/tourer-2008/43190/

Btw, where can I find out the difference between the various Honda Accord models:
ES, ES GT, EX GT, Type S, EX ?

J


P.S. My last car was a 2007 Honda Accord 2.2L i-CDTI. I was broadly very happy with it. One problem was that there was quite a lot of 'road noise' from the tyres when driving on motorways. I tried changing to quieter tyres (rather expensive winter tyres in fact) which helped a lot - but even so it was still quite noisy. How do the 8th Generation compare with 7th Generation for 'road noise' ?

ship69 said:

Racy Jace - Yup Those stats sound good. But I'm confused... is that a screenshot of the dashboard or what?

Even without a remap according to Parkers the stats for a Type S are pretty good:
49 mpg, 177 bhp, 0-60 8.5 secs

http://www.parkers.co.uk/cars/reviews/facts-and-figures/honda/accord/tourer-2008/43190/

Btw, where can I find out the difference between the various Honda Accord models:
ES, ES GT, EX GT, Type S, EX ?

J

Click to expand...

The screen shot is of the app I used (Torque) that was linked up to the OBDii port via bluetooth. The 0-60 used the GPS and the speed to calculate it and apparently is quite accurate.

I have an EXGT and I did a trip from my house to Manchester airport and back and got 56mpg at 80mph. Most people would drive at 65-70 to get better MPG but I just wanted to get my holday started ASAP . My journey to work is now 39 miles a day driving from Upper Gornal to Telford. My area is quite hilly as we are high up so what I gain going down hill I loose going up it. Its a mixed journey but maily on the B4176. I get around 49-50mpg after 5 days. which equalls 195 miles a week I think. If I pop to the shops and sit in traffic doing short joyrneys it will drop to 45mpg

I had a brochure that has the specs in so I just had a quick look. Im sure the Honda site has it in PDF format.

One thing that still confuses me as that the different IDtec models have different emmissions and MPG. I think the EX GT is the worst according to Parkers and the Auto Trader. ??

If youve the money for a Typ-S then that would be my choice. Its quick out the box and has clear Indicators

> 56mpg at 80mph.
That's pretty respectable. But Is that 80mph on the speedo or using GPS. (On my old Honda Accord Type 7 a speedo of "80mph" was really about 75mph on the TomTom satnav.)

My target overall would be at least 55mpg on long journeys - although I think the computer was persistently under-estimating the fuel used.

It was on the speedo so actually it would be around 75 mph on the gps. Tyre pressure seems to be a big factor so keeping an eye on them helps a lot.

Honda auto's seem to be really woeful,slow,old,clunky, uneconomical. Why they don't go dual clutch and be done with it. They have on the new VFR bike which has dct a first !!!

I am a bit confused about Honda's MPG figures.

e.g.
On Autotrader for my 2007 manual EX i-CDTI, the Combined MPG is given as 47.9 and Extra-urban as 57.6, split the difference gets you 52.75 which is about what I used to get on my 40 mile commutes.

On Autotrader, for 2009 auto EX i-DTEC, they are quoting Combines MPG as 44.1 and Extra-urban as 53.3, split the difference and I would hope to get 48.7 MPG.

HOWEVER folks here are saying that you'd be lucky to get more than "41 to 43 mpg" even on motorway long trips. If so are Honda essentially lying about "Extra Urban of 53.3?

Or could it be something to do engine wear or with DPF problems... or dare I say it driver skill??

Something doesnt fit here... !

For a start extra-urban isnt motorway, its a mixture, see the definitions here:

http://www.dft.gov.uk/vca/fcb/faqs-fuel-consumptio.asp

I think the people who say 41-43mpg out of a diesel auto on the motorway arent right. Depends how fast they go for a start. Maybe those figures are right crusing over 80mph or more.

I get 40mpg out of my 2.0 petrol auto on the motorway, thats taking it easy, 70mph ish, if I go faster I'm down in the 30's mpg.

Take a test drive in one, reset the computer and take it up the motorway, see what you get?

If you want better consumption you've got to look at smaller cars than the Accord; Civic, Golf size etc

Dont get too obsessed with consumption figures, its the total cost that counts, road tax, purchase price, servicing.

I know several idiots who have sold perfectly good young cars to get a car in the free road tax band, they dont seem to consider the several thousand pounds they had to pay to avoid £215 road tax each year?!

I take your point about cost of ownership... but it's a tricky calculation.

Regarding the MPG component, I do about 22,500 miles per year.
By my calculations, a petrol car doing overall say 35MPG would cost about £4090/year,
whereas my old 2007 diesel (i-CDTI) would do about 50MPG and would cost about £2950/year.
==> i.e. a saving of £1450/year by running diesel.

Regarding the purchase/sale price although a 2009, 60,000 mile diesel is about £1600 more expensive than a 2.0L petrol (2.0 i-VTEC ES GT 5d), given that I am planning to run my diesel into the ground (***uming I dont crash it - ahem) over the next 8 years or so then more important is that a) the diesel engine is likely to last longer and B) every single year of ownership I will be saving a further £1400 or so in fuel.

So, so long as one doesnt SELL the car, a diesel would seem to make more sense, no?

ship69 said:

So, so long as one doesnt SELL the car, a diesel would seem to make more sense, no?

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you'd probably get a higher re-sell price too

Completely agree with the running it into the ground theory, gets maximum value out of the car.

If you plan 8 years @ 22500 a year, I'd recommend getting a car with 40k-50k miles on max, so it will be around 200k miles when it dies. if you buy something already with 100k miles on, it wont take long before the big bills roll in.

I'd still have a petrol, but thats my opinion, there is simply a lot less to go wrong. Diesels have injectors, turbos, intercoolers, dpf etc etc.

Also I'd recommend a manual, not sure an auto would make 200k, and dont remap it, keep it standard and change the oil every 6k or so.

Anyway whatever you decide, all the best.

richsprint said:

Also I'd recommend a manual, not sure an auto would make 200k, and dont remap it, keep it standard and change the oil every 6k or so.

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Any particular reason why not to remap it? I rather liked having my last car re-mapped... I didnt use the full power very often as I was keen to keep the overall MPG up to something sensible... but it was very good to have esp for over-taking. Are you simply concerned about general wearing out the engine or something more specific?

Also what is the life expectancy of an automatic gearbox and what most likely to go wrong? As far as I could see an automatic gearbox is all about sloshing oil (rather inefficiently!) around the place with surprisingly little metal on metal contact... and so not very much that could go wrong! No doubt they are absolutely horrendously expensive to replace from new from theiving Honda (although I dare say one could get one from a breaker's yard cheap enough if necessary...)

Re oil change as recommended somewhere on typeaccord.co.uk, I bought a big barrel of special stuff from LubeTech ("OPTIMA 0w/30 BMW Longlife 98. Fully Synthetic Engine Oil" to be precise) which I was rather hoping to keep using - although I am now a bit worried that if I get an 8th Generation it will have a DPF and perhaps using that oil would not be a good idea. :^/