I am interested in a Vauxhall Zafira 1.9 diesel with a 6 speed automatic gearbox. When in D (drive) i can flick the selector towards left and change the gears manually. When in D i noticed that at around 50mph the car is in 5th gear (dashboard display tells you what gear you are in). I can select 6th gear manually with no problems.
I know that automatics are less economical than manual gearbox. If i change the gears manually can i improve the mpg figures? Hope i make sense.
Before anyone says buy a manual i have problems with my legs and find using clutch a problem sometimes.
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I sometimes drive my partner's automatic and find that, around town at least, it is usally one gear lower than it could be and is revving quite hard so I manually change it up to 4th. She isn't very technically minded and just lets the auto box get on with it, to the detriment of her fuel consumption! That said not all autos are bad for fuel consumption; I understand some Mercs give better figures with auto boxes than manual.
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I have a Kia Ceed automatic and my fuel economy figures are within 90% of quoted by Kia.
Mine is a conventional auto (torque converter) and I noticed that it upshifts quite aggressively. On a level ground at ~35 MPH, it shifts to 4th gear (which is top in auto and by gear ratio value it is comparable to manual's 5th gear)
I believe automated manuals are designed so that ECU won't allow engine to stall. You can always upshift and if that's too ambitious, ECU will downshift for you.
Why not try for few days and see if you got better fuel economy?
corrected an innocent word picked up by the swearfilter
Last edited by: VxFan on Thu 2 Sep 10 at 00:56
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Depending on who makes your auto box, it may be possible to install alternative software on it to change it's behaviour. If it's a ZF box you can contact ZF sales in the UK (they're in warwick IIRC?) and they'll be able to put you in touch with the right people (and i don't think it's massively expensive either).
A fairly common one to change is the VAG DSG gearboxes by BorgWarner. They come with the opposite from your case, their software changes up too soon for economy and a few other niggles. However new software (which was originally based on the original software, just tweaked) is available from a few vendors.
Biggest one i know of is Revo, who VAG themselves have used on a number of occasions for "special" cars.
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There's an implicit assumption in the question that using higher gears at low speeds will improve fuel economy. I have little experience of driving automatics (and none of measuring their fuel economy) but I've monitored the consumption of my manual cars over 20 years. In 1996 I was persuaded by an advanced instructor that driving in third gave better control than my habitual fourth in 30mph zones. My fuel records from that time show no upward step in consumption (petrol at the time), which makes me think that consumption I'd more to do with the combination of power and torque being demanded of the engine than with rpm alone.
Since moving to a turbo-diesel I've become, if anything, more aware that changing up early risks dropping the engine into its off-boost flat spot, which requires more right foot - and hence more fuel - to maintain progress. In contrast, it's perfectly happy to trickle along in third with foot merely caressing pedal.
NC can supply the engineering logic, but I suspect anyone who tinkers with gearbox programming in the hope of an extra mpg or two is on an expensive hiding to nothing.
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Many moons ago I borrowed an old shape 1.8l automatic Vectra for 5 days.
Around town I had to use the sport button to make any progress at a road junction or roundabout.
The fuel economy was dire around town.
The fuel gauge would move as I turned a corner and never reach were it was before turning.
I.e. it drank fuel.
However once on the motorway the fuel economy was excellent (for a 1.8l).
The engine revs were around 1,700rpm at 70mph so it just sipped fuel.
The only problem was that if any hill was encountered then a heavier right foot was needed and if it were a big hill then a kick down was needed just to keep 70mph.
I never did work out the fuel economy but £15 of fuel lasted 4 days and covered 130 miles.
I still think a diesel engined car with a manual gear box is better though.
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>>which makes me think that consumption I'd more to do with the combination of power and torque being demanded of the engine than with rpm alone.
Exactly correct WDB.
Reducing the maximum speed at which you travel is a very good way to reduce the power demand - even a small reduction in speed when travelling quickly can give a much greater increase in economy than tweaking gearing. This point came up recently in the optimum speed thread.
What might make a real difference with a modern automatic gearbox is driving it such that the lockup clutch in the torque convertor is activated, thus preventing some of the fuel's energy being wasted in fluid slip.
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>> I still think a diesel engined car with a manual gear box is better though.
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Seconded, I would be flexible on transmission type as long as there are no milk float components involved.
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Buy a Prius, Auto box and 60mpg (real world mpg).
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I used to drive an auto Merc. And an auto Jag.
Best way to improve fuel consumption is to prevent torque convertor slip as much as possible as that is a direct waste of fuel.
So accelerate slowly, don't accelerate up hills, accelerate down hills. and try to drive on the overrun..
I managed to get 28 mpg on the Mercedes on a long run. And 23mpg on the Jag..:-( (and 16mpg towing a caravan eek!)
If I did not try I could get 25mpg and 19 mpg respectively...
I also drove an auto BMW 535... I never worried about fuel consumption just worried about the (lack of) traction in the wet..
Last edited by: madf on Wed 1 Sep 10 at 19:30
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Can i improve economy of an automatic? - Perky Penguin
