What is the difference in fuel economy between the TD4 manual and auto down to? Is it different gear ratios, or is it just the fact that an auto isn't as intelligent as a human (e.g. it can't read the road ahead)?

If it's the latter, should it be possible (at least in theory) to replicate the efficiency of the manual box by using CommandShift on the auto box?

Automatic transmission relies on a torque converter to transfer the drive from the engine to the gearbox, it is simply a function of how a torque converter works that there is slippage in this system; that means not all the engine revolutions are transferred to the gear/wheels. Watch the rev counter when moving of in an auto, it will quickly climb to say 2500 rpm (depending on how for the accelerator is pressed), then hold while the car accelerates to match the speed of the engine. Modern torque converters and auto boxes are way more efficient than their predecessors, so the mpg comparisons these days are much better than they used to be. But it is highly unlikely an auto will ever match a manual.

The gear ratios are nearly identical in both manual and auto boxes on the FL2, I think it is only a very slight difference in the first gear ratio that sets them apart. At speed the torque converter is running at very high efficiency (but probably not a full 100%) which means that prolonged constant speed running like motorway cruising will see the autos fuel consumption at its very best, and maybe quite close to the manual.

One question I have asked of LR, which has not yet been answered is whether or not the torque converter has a ‘mechanical lock up’, the does as it says in that it locks the two parts of the torque converter together meaning it is 100% efficient, although it has to disengage at lower speeds to allow for gear changing. Anyone know if the auto has a lock up on it.


One feature of a manual box is that the drive can change up at lower speeds than the auto box will allow, this will improve fuel consumption at the expense of performance. Auto boxes are getting much more sophisticated, with sport programs which will hold the gears for longer, making for better progress but at the expense of fuel consumption. They also have intelligent or adaptive modes where they learn to replicate the style of the driver, so if you a laid back and out for a slower ride the box will learn this and makes its up shifts earlier, probably improving fuel consumption but at the expense of performance.

Hope this helps .... have been around autos for over 35 years ...

Great answer, thanks for taking the time to write all that!

Avtur, the FL2-automatic does lock the torque converter, as we are talking of a modern 6-speed automatic gearbox designed and manufactured by ZF, Germany, a well known gearbox manufacturer. I do not agree with you that no automatic gearbox will match the manual gearbox fuel consumption. My office-car, a Mercedes 320 cdi 7-speed automatic (Mercedes own design and construction) consumes 0,3 litre/100km less than the same car with manual gear box. This is a fact proven by acribic noting down of tank fillings and driven km (demand of our tax authority).

YF

yamaha-fan wrote:

Avtur, the FL2-automatic does lock the torque converter, as we are talking of a modern 6-speed automatic gearbox designed and manufactured by ZF, Germany, a well known gearbox manufacturer. I do not agree with you that no automatic gearbox will match the manual gearbox fuel consumption. My office-car, a Mercedes 320 cdi 7-speed automatic (Mercedes own design and construction) consumes 0,3 litre/100km less than the same car with manual gear box. This is a fact proven by acribic noting down of tank fillings and driven km (demand of our tax authority).

YF

Back into mine at NightFoxes simple language and understanding, I find yes!! Switching to command shift I can get better fuel efficiency than std auto mode as I change up the gears sooner than the autobox would. In my manual days I'd be in sixth if just cruising down the 'A507' at 50, in the auto it is still in fifth

Well my dealer's lending me an auto until mine gets sorted, so when I pick it up this weekend I'll have a play.

When I had my D3 TDV6 auto I tried to get into using the manual change, but after a bit I just got too lazy to "learn" and just left it in "D"

You will love it NF takes a few miles to get used to which gear you are in command shift, and your early days will probably have shocking MPG as you just floor it everywhere...then you start to 'drive' it and settle into it, I'm well chuffed with mine

Don't want to like it too much for when I get my manual back!

Then again, if I can get good mpg out of it, it's something to think about if..... no, let's not even go there yet!