2.0 TDI best RPM for MPG

[sukrw]

Hi all,

Interested in peoples views/thoughts on the best rpm at say 30 to 40mph to obtain the best mpg in a diesel (mine is A3 2.0 tdi 140). First Diesel I have had and only had it a few weeks.

I assumed it would be low revs so have been driving around towns and slow dual-tracks (40mph) in 5th and 6th gears. Ok, not planting my foot on the gas pedal but letting it slowly build speed.
When coming to inclines moving down to 4th to prevent the engine from labouring (going below 1000rpm).

Anyone got any views on this ? Better to keep the revs a bit higher ? even tho there are gears left that will happily keep the car at a constant speed ..?

Ta.

 

[Crisis]

Well I feel for 30mph it depends if its a free flowing 30 or a slow 30... if that makes sense.

Generally I used to put cars into highest gear. I feel the A3 2.0TDI 140 doesn't like going below 1200RPM, put your foot down and nothing happens. So not good. 1400RPM is probably what I let it sit at minimum.

1400-1800RPM with MIN and MAX 1200 and 2000 respectively.

Thats how I drive it anyway.

 

[emzino]

30-40mph > 4th gear @ 1500-1800rpm. I'll never go anywhere near 5th gear unless i'm doing 50mph+, it's just to high a gear for it to be in while doing 40-50 i've found. Has to be above 50mph

 

[Twizzler]

I would expect the most economical speed to comply with the rpm at which the engine develops its maximum torque.

 

[Crisis]

Isn't it more of a point of no need to exceed that point? As it just drops off? And I dont know if the torque curve flattens off?

I've read diesel engines generaly shouldn't need to exceed 2,000RPM to keep MPG up.

Anyway Max Torque is at 1750RPM.

 

[Crisis]

Also to note: Obviously you can't be at 1750RPM all the time, so it is better to be say 1500RPM or 2000RPM? Higher or lower?

 

[Twizzler]

I would expect the torque curve to increase steeply at lower revs until it hits peak then have a slow flattish roll off to 4000rpm or so then start to roll off steeply to max revs.

 

[Boydie]

I am now changing gear higher up the revs - over 2k anyway since i have some clutch issues it seems to have temporarily solved the problem for now - probably is affecting my mpg slightly but the other day i got 50.4mpg for an hour long trip of mixed driving :O

I am usually getting around 45mpg or less!

 

[benw123]

The answer is as low RPM as possible without the engine labouring. This means just over 1000rpm, but if you're hell-bent on economy then don't go over 2000rpm.

It does make a difference. When my brother recently moved house, I followed him in his hired Transit Luton for a journey of around 30 miles at an average speed of just 40mph along the A12/A14. Towards the end of the drive I switched over to DIS to see 63.7mpg - I was impressed!