[philreid]

I've got a 325i M Sport with the 3 litre engine. It's an auto and I'm getting an average of 26.7mpg combined which I hoped I could improve.

I normally drive it around town in automatic mode and use manual when I want to be a bit more involved in the drive.

But I wondered: is it more economical to drive in manual mode?

I obviously don't have the gear shift indicator, so when driving it in manual, at what point is it good to shift up when trying to save fuel and without making the engine labour?

I notice the auto box changes up at about 2,500rpm in normal mode.

Cheers.

[doughboy]

I would say no, auto mode will shift at the optimum point for you. Modern autoboxes are programmed to quickly shift up under light throttle at the optimum revs to give good mpg.

If you shift when the autobox would then you'll probably already be at the optimum shift point.

That's why modern autos have 7 or 8 gears now, nowt to do with performance, it is simply to increase mpg on light throttle by quickly shuffling to an unfeasably high gear to keep revs down.

These 'super gears' are only ever used on a very light throttle down hill or level. Any more than a light throttle and it will shift down. This is essential on the emmissions tests as they are all based on very gentle acceleration and decceleration at fairly low speeds. You only have to read the latest Porsche turbo PDK review to see how it gets into seventh gear by 30 mph!!

[HighlandPete]

With a light throttle the box will be running one of the two ecomony programmes in 'D' anyway.

You will find if you use the manual function and try and change too soon, the box won't do it anyway. In my experience the only real place I find flicking to manual and up changing assists economy, is where the traffic flow (steady speed) is just too slow for an auto up change, but will hold a manual change. An example for my 330d is cruising, at say 45mph, the auto needs about 48mph to change to 6th, but a manual change will select 6th and it stays there, unless you drop to about 41mph. Then does its own down change... we speed up a bit and I'll nick it back into 6th.

I've driven from home to the Isle of Skye many times (100 miles) and the OBC shows virtually the same mpg, whether in D, or I work the step' function all the way.

HighlandPete

[Jon D]

I agree with Highland Pete and Doughboy. I now hardly ever use the paddles on my 330d as I find the auto mode excellent; however, I sometimes override it on long descents in traffic to provide additional engine braking. If I want to press on around the bends I select DS and that seems to give quicker down-shifts just when you want them, but that's probably because you're already in a lower gear as opposed to D mode. Either way it works fine for me and I have to try really hard to get worse than 35 mpg. The other day I had the car loaded up and consequently had to limit cornering fun, so I drove uncharacteristically sedately from Inverness to Aberdeen and averaged 51.3 for the trip - what a car.

[philreid]

Thanks for all the info chaps - appreciate it.

I kind of thought the auto box would be designed to get the best economy out of the car. Problem is that I find it to be a little slow in responding and sometimes feels a bit 'spongy' if that makes any sense whatsoever - when I press the accelerator it seems to take a wee while to respond. I suppose that's some kind of fuel saving mechanism?

When I'm in manual mode the car leaps forward like a bat out of hell when I put the foot down, but suppose that comes at a cost.

I'm gonna get a 330D when I change this car in a couple of years, especially if petrol-diesel prices stay this way for the long term!