Hi,
I'm in the process of choosing my new car and a question has popped into my head and I'm sure that you guys will know the answer.
I'm looking for a diesel car that offers good economy driving at 70MPH on the motorway. 85-90% of my driving is on the motorway, long disctance and a constant speed. Very rarely do i do short journeys.
My question is concerning auto diesels. When the auto's are crusing at 70MOH, surely thay are in 'top gear', no power loss is being lost by the torque convertor (as it's not needed) so therefore are diesel autos as ecomonical as manual gearboxes when crusing at a constant 70MPH.
The reaosn I ask is that I do need economy (40,000 miles per year) and when I look at the 'official' fuel consumption figures, the auto's are quite a bit down on the manual's when you compare the combined figure but I am guessing that this is skewed by the auto being significanly less economical in the urban run and therefore affecting the combined figure.
Right or wrong?
Also, recommendations of economical diesel auto's most welcome. I'd quite fancy a passat but a combined figure of 42MPG is a bit low.
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Have the Golf 2.0 TDI 140cv DSG. My long term average over 27,000km is 49.1 mpg. Live in a rural environment, so not much urban work, combined with long motorway trips. Recent 2,500km round trip on motorways with cruise control on at 115+ kph gave 5.46 l/100 km (51.7 mpg). Use BP normal diesel. Guess the Passat will be heavier, so that will affect figures - Golf combined figure is 5.9-6.1 l/100km (47.1 mpg).
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I'm getting 42mpg overall at the moment from my manual Passat 100PS estate.Ditto a recent motorway trip up to Scotland. I'd expect an auto to use even more.
--
I wasna fu but just had plenty.
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DSG isn?t a conventional auto ? it doesn?t have a torque converter.
Most auto?s now have a lockup clutch which locks the torque converter at speed, so there?s no losses through it. Another thing is that auto?s sometimes have higher overall gearing, so at a steady speed the engine is running at lower revs.
Stop/start driving kills the economy of diesel autos ? I have Merc C270Cdi (auto) and short journeys can result in the trip display showing 30MPG. However, just like you, I really only use it on long motorway runs, where a steady 70ish has high 40?s and sometime 50MPG showing in the trip (which is, unusually, spot on compared to brim to brim refuelling).
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Yes, Bill Payer is right. I had exactly the same consumption from my C270CDI auto.
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I've been running a Volvo D5 Geartronic for 3 months and 5000 (mainly motorway) miles. Combined consumption is around 38.5mpg, which to be honest is reasonable I think. I often run on continental motorways at 85-90mph, and I think many people expect too much from diesel engine economy. It's a 5 cylinder 2.4 engine and I don't think I can reasonably expect to get much over 40mpg, unless I'm driving very carefully at 50mph on quiet roads all day!
I laugh at people who buy a large-ish car with a 2-point-something engine and just because it's a diesel they automatically expect to be cracking 50mpg every day.
People's own driving habits and styles must make a huge difference to economy, regardless of engine type or size?
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Ive been running around in a VW LT35 95 van the last week and im getting mid 40's mpg from what is a very large ( if empty ) vehicle. Ive done 260 miles on £22 worth of diesel - far more than I was expecting from mainly town work and A-roads. Like you say, its down to how you drive them sometimes.
That Volvo isnt doing so well really tho - My mums Hyundai Coupe V6 does 35 mpg on the motorway and thats from a rather archaic old-syle V6 petrol. Only does 22mpg round town tho!
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My A3 DSG 2.0TDi does about 45-50, more on longer runs. Performance is very good too. I have the 140 BHP not the 170.
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>>85-90% of my driving is on the motorway, long disctance and a constant speed.
Same with me and for that reason I chose a manual with a 6 speed manual box. The sixth gear gives long legged cruising on the motorway and I find I hardly ever have to change down for inclines or to build speed back up after slowing down. The VAG DSG auto seems to give as good economy as the manual but I don't know how high it is geared in its various applications for motorway cruising. If it is a company car most automatics will clobber you on CO2 and BIK.
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That Volvo isnt doing so well really tho
Well, 38mpg S60 diesel with geartronic reaches 60 in 8.4 seconds. I think it's doing just fine...
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[Nissan 2.2 dCi are NOT Renault engines. Grrr...]
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DSGs and automated clutch gearboxes give the same MPG as a manual, if not better, because there is no power-sapping torque converter. DSGs and automated clutches are often more economical than manuals because, in auto mode, they don't over-rev or otherwise abuse the operation.
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VW won´t build any more conventional torque convertor gearboxes into future tranverse front-drive models. Also stop-start systems to be introduced. They´re developing a DSG for the new Polo out next year.
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FWIW, I have a manual S60 D5 (although with the 163hp version of the engine that was current in 2002) and have averaged 43 mpg over four years and 50,000 miles. My fill-to-fill figure has never exceeded 47 mpg, although that's partly because a tankful goes so far that I've never done one that was entirely motorway travel.
IIRC, the difference in CO2 from manual to auto when I was choosing was huge - 171g for the manual and about 200g for the auto. When you consider that the auto box takes away a lot of what makes a good diesel so pleasing to drive, the appeal of an auto is rather lost on me - after all, I can drive the manual almost entirely in third around town if I'm lazy enough. (And the S60, unlike the Audi A4 and some others, has room for three pedals and two feet in the same footwell.)
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This has be discussed several times.
From a previous theread:
HJ wrote in Car-by-Car breakdown "Steptronic auto increases fuel consumption of 330D by around 25%."; and I have seen this point made in other publications.
There was a thread covering this:
www.honestjohn.co.uk/forum/post/index.htm?t=11847
The most plausible explanations for this stated
"I suspect that the reason many diesel automatics do not show good fuel consumption figures is due to the high engine torque at low revs, which maximises torque converter slip. Coupled with the weight penalty of a diesel, this is a sure-fire formula for bad figures unless the box has a torque converter lock. ....... Around town, an automatic gearbox is using the torque converter as lock-out doesn't occur until 50 mph, or thereabouts. The gear ratio might be slightly more efficient but the torque converter efficiency is quite poor."
As economy is the main reason for most people buying diesel, perhaps this is why few diesel automatics are produced.
See also
www.honestjohn.co.uk/forum/post/index.htm?t=32503&...f
www.honestjohn.co.uk/forum/post/index.htm?t=26531
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I was with someone today who has a new S type 2.7 diesel auto. On a steady run from London at the weekend he managed 43 mpg.
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As economy is the main reason for most people buying diesel, perhaps this is why few diesel automatics are produced. See also
They still have much better fuel economy than an equivalent petrol engine, particularly in urban driving.
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I agree with the suggestion of the Golf TDI 140 DSG: if this is too small (you were thinking about a Passat), go for an Octavia 2.0 TDI 140 DSG - more car than the Golf for about £2,000 less.
You can get the 1.9 for even less, but they are sluggish in comparison - read the thread on here '6 months with a Skoda' which is very helpful.
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I was going to say that at constant speed a modern automatic should be no less economical than the manual. But if you are spending so much timeon the motorway - why buy an auto?
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I was going to say that at constant speed a modern automatic should be no less economical than the manual. But if you are spending so much timeon the motorway - why buy an auto?
Because I am the laziest person I know!!!!
It's fair to say that although most of my driving is on the motoway, the vast majority of the rest is in central london and that's what I really want the auto for. I know the MPG is destroyed in London so I am parking that to one side for now.
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85-90% of my driving is on the motorway, long disctance and a constant speed. Very rarely do i do short journeys.
Doesn't that mean the auto is effectively redundant for 85-90% of the time too?
It seems quite a premium for so little return.
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I didn't copy Aprilia, honest.
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Need more coffee, should have been Espada...
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The C4 HDI 110 with the EGS (electronic gear shift) 'box has lower emissions than the manual - and as they are only 120g CO2/km will qualify for exemption from the Congestion Charge later this year/early next year. Which is why I'm seriously consdiering one.
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A real world example...
We have a Hyundai Trajet Diesel Auto, which manages about 25mpg around suburban Manchester with my wife at the wheel. This equates to about 300 miles per tank. When we go on a long trip - say to London - I drive and keep the speed to below 75mph, I can get over 500 miles to the tank if I kept going non-stop. If I drive faster and keep the needle over 80mph, the tank will only go for 450 miles.
I certainly agree that if you drive in urban London, you would want an automatic!
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The C4 HDI 110 with the EGS (electronic gear shift) 'box has lower emissions than the manual - and as they are only 120g CO2/km will qualify for exemption from the Congestion Charge later this year/early next year. Which is why I'm seriously consdiering one.
It would interest me too but I bet the chances of a test drive in one are close to zero.
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My car isn't suitable for the OP as he wants a car that will give over 42mpg on a motorway run ------- but over a 250 mile, 85 mph run yesterday, my diesel automatic 300C pitched in with 41mpg, which I think is rather splendid for such a big fella.
MTC
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