If I may take the "Auto Vs Manual" question one step further and combine it with perhaps one the most divisive and contentious issues on this forum - "Petrol Vs Diesel" and concentrate specifically on diesel autos.
In general, is a diesel engine's characteristics more or less favourable to mating with an autobox?
Reading various road tests over the last few years, it (perhaps naturally) seems that the individual road tester's preference seems to overshadow the overall opinion - for example when the E39 530d was launched some mags said that the huge torque available low down the rev range was better used by the steptronic box but some said it was better suited to the manual.
Chad.
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Okay I'll start the ball rolling.
My last 3 autos have been diesels and I've got no complaints at all. Especially suited to the heavy towing I indulge in.
Not a question of good or bad though, it depends on the match of the engine to the gearbox. SWMBO's Berlingo diesel (normally aspirated) would be dire if it were auto. My 3.1 TD Jeep is a dream.
--
Terry
"Just because I don't care doesn't mean I don't understand"
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Chad,
There was a thread on this subject a year ago in the technical matters section see:
www.honestjohn.co.uk/forum/post/index.htm?t=11847
C
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I've posted this on the other thread on auto v manual:
The Audi A4 TDi multitronic (ie a CVT) automatic gives a combined fuel consumption of 51.3 mpg compared to the manual's 50.4. The multitronic also produces lower CO2 emissions 149 g/km v 151. The manual version is marginally quicker to 60mph: 9.9 seconds v 10.1 seconds.
The Audi appears to get round many of the problems by having the CVT.
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The high torque over a narrow rev range make the auto box well suited to the diesel engine. Also the intial turbodiesel lag is erased by the torque convertor which would need some awful clutch-burning to achieve in a manual.
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The high torque over a narrow rev range make the auto box well suited to the diesel engine. Also the intial turbodiesel lag is erased by the torque convertor which would need some awful clutch-burning to achieve in a manual.
But often(in a diesel) at the expense of of much worse fuel consumtion than the manual version. The differential is not so marked for petrol versions of the same model. As increased economy is one of the major reasons for buying an oil burner it lessens the appeal.
The last post in the technical discussion(see link) gives a plausible explanation for this reduced economy.
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never driven an auto or diesel but tried a bmw 330D sport auto last week and was completly blown away. so powerful, quiet and nice to drive. i want one!!
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After nearly 2 months and 3,000 miles with an Audi A4 Avant 'multitronic' (2.5 TDI) I'm still very much smitten.
The only slight downside to diesel / automatic is that, compared with my previous VW GOlf TDI (manual) it's a little slow immediately off the mark - because diesels, especially turbodiesels, don't have much oomph below 2500 rpm. But it soon gets going and it's a small price to pay for the convenience of the auto.
It has tiptronic enabling you to change (imaginary) gear if you want to, and a sport setting to hold the lower 'gears' for longer. Average mpg about 6 mpg worse than the Golf - no more.
As someone has said, you do need a big engine to take an auto without it feeling sluggish - 2.0 litres minimum and ideally more.
Let's hope that the multitronic is reliable! My last auto was a Laguna V6 which - Honest John won't believe this - never went wrong in 97,000 miles.
David
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Thanks for the link Cardew and to everyone else for posting, I'm coming to the conclusion that the answer to this question is another one of those slighty grey areas....
Chad.
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Something not mentioned on either thread is something which for me is a pro "diesel - auto" issue. The very low max revs of the diesel results in first gear tending to feel quite short.
To give just one example, entering a busy and quick flowing roundabout from standstill often entails a quick get it rolling in first followed by a rapid change into second and then gun it. Seems to me that an auto would dispense with the "hazard" of a missed / snatched gear change at a critical moment.
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Not in the Allroad it doesn't. I didn't mention it in the testdrive thread, but the box always went for "first" when pulling away from around 5-10mph where I would use 2nd and the higher torque of a diesel if in a manual. This often left me in "crawler" mode, having to put the pedal down quite hard to get the car up to speed. The box wasn't in Sport mode when this happened.
Had I been using the semi-manual mode I could probably have dealt with this, but at the end of 40 minutes I still wasn't able to second-guess the transmission when in full auto.
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I had a BMW 525d auto for assessment a couple of years ago when I was changing my company car. I was awed by it - stunning performance, smooth auto, shame I couldn't really justify the extra cost! But I'd have one tomorrow if I could (please please please!).
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Maybe so ND, but that is a different case from pulling away from stationary.
Shirley the example you give is more a case of an auto box not correctly set up to take advantage of diesel torque.
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Maybe so ND, but that is a different case from pulling away from stationary. Shirley the example you give is more a case of an auto box not correctly set up to take advantage of diesel torque.
LOL, Shirley !!! Is that ND's new nickname! :-)))
Chad.
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Something not mentioned on either thread is something which for me is a pro "diesel - auto" issue. The very low max revs of the diesel results in first gear tending to feel quite short .....
FiF, that is exactly the reason that I wish I had gone for the auto box in my Rover 75 CDTi. I bought this diesel for the way it drives, not really for the economy (only about 6,000 miles/annum) and I am extremely pleased with its performance other than that slow pull-away.
"Flat in First" is how I would describe it.
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As has been mentioned already the BMW 3.0l diesel is an awesome motor and when linked to an auto box it gives you quite a few options on how to control, full auto, sport, raising the change up by about 500 rpm and smg push buttons for up and down, although it won't let you abuse it.
I have not used it for towing but I can say the inertia, much bigger and heavier roatating components to cope with higher compression, and the turbo lag do make it hesitant for half a second, compared to the 3.0l petrol. However when it's rolling it is very strong and gives a tremendous amount of torque, 500 nm that makes driving effortless and overtakes easy.
I am buying the same set up again in a new 530d touring but would want to test drive any other combination before committing to it.
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Hi
"Flat in First" is how I would describe it.
I drive Citroen C5 2.2 Auto diesel.
Very good combination, smooth, lots of torque but very slow from dead stop to 2nd gear. Therefore no nipping out at junctions, more a stately wallow.
By switching box to 1st "manual"/sport the car is more responsive.
Generally its a very good match. I'm a convert.
regards
Vercin
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Re fuel economy from a diesel-engined car with auto box, my Terrano 2 actually has a higher top gear ratio than the manual even though it is only 4 speed. Couple this with a mechanical lock-up when cruising and it is likely that at motorway speeds the auto is more economical. Of course stop start and urban motoring probably gives a worse figure.
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