Driving efficiently... how do you do it?

Following a conversation in the office, I came to the .Org to post the below, but given what I read when I logged in, I thought it more appropriate to wait a while. Anyway...

Conversation in the office about fuel economy, and a couple of the lads in the office now hate my guts. As I recently posted, the bike has been sold, and as some know, I've replaced it with a turbodiesel car. The reason the lads don't like me is that one of them is getting 18mpg from his car, whereas I get 51mpg without even thinking about it.

As I'm pretty new to the turbodiesel world, I thought I'd come & see if anyone had any tips for driving more economically (so I can wind them up more).

I'm aware of coasting, keeping revs as low as practically possible whilst accelerating, leaving the brakes alone, using 5th where possible etc. I'm also aware that on over-run, the engine uses practically zero fuel (useful when you live in an area with a large number of hills).

But is the rev-counter the same as most, where generally peak torque happens at the top/centre of the rev-counter? Also, driving "on boost" from the turbo is likely to be more efficient but that's probably going to be a fine balancing act (as fuel usage could go up with more forced induction from the turbo).

Anyone got any tips for driving a TD engine economically?

TIA.

Basically the turbo uses loads of fuel (but diesels are still very frugal). Built up areas kill MPG but you'll always get over 40 and if you are good you'll see 70 mpg or thereabouts on a motorway, my old cavalier TDI used to do about 67 on a run so new ones must be ace. Oh and rev relatively low and change up early to save the most gas 2k-3k change etc. Diesels make all their torque at about 2500rpm. I loved the money saving but couldnt stand the noise and engine characterisitics thats why i got a 528 auto petrol beamer. Smooth as silk and 24mpg round the doors with 30 on a run.

Originally Posted by Jackie_Black

Oh and rev relatively low and change up early to save the most gas 2k-3k change etc. Diesels make all their torque at about 2500rpm.

I've been changing under 2k and running on average around about 2200RPM today (since the conversation). It's a 1.9l engine, so plenty of pull at low revs.

My commute consists of mainly NSL area's, so built up areas aren't going to be a problem. It's not a new engine, but there's sod all wrong with it. 10 year old engine, and it'll happily idle iself all the way up a 1in7 hill (no feet on any pedal)!!

Bit numb with the other news, never met him, can't say as I agreed with much he wrote but damn if we ain't lost a character with a good heart.

Anyway, I guess this thread is serving the keeping mind off it principle.

So 50 is about what I've gotten from just about every diesel engine I've owned from 1.9td pug/citroen units to 2.5 VAG plants. And yeah, it's not something you really have to think about, I guess it's something about the power delivery that just makes you drive in a more relaxed way and shift up early rather than race to peak power in a petrol. That said, a lot of the newer engines feel suprisingly petrol like.

Personally when in "just get me home it's raining and I'm miserable" mode I find myself shifting up very very early. Peak torque is going to be in the handbook or a website someplace but I've never driven a diesel car that isn't plenty happy shifting up at sub 2k rpm. Hell, they'll change all the way up to 5th/6th on tickover even if you're quite brutal with dumping the clutch. I'd think that driving off boost where possible is likely to be more economic - boost gets more air in in-order to allow more fuel to be pumped in, at off boost levels I'd imagine the mixture ratio is still the same it's just that the airbox is able to supply all the air that's needed.

On the motor I had I always found if I kept it between 2-3k it was happiest and most frugal. Of course they all feel different so if you can rev less and get away with it then thats good. The cavalier needed to be on boost to actually move and was terribly flat without it so for safety i was always between 2 and 3. If the revs dropped too low I always felt I was labouring the engine too much and the vibration was awful.

Most of those above you've got are pretty much it, one other essential one:
If you're coming to an uphill, and you're currently on a downhill, speed up slowly as you are coming down the hill (using minimal additional fuel as gravity will be doing most of the work) and allow that extra speed to carry you up the hill that little bit more, therefore using less fuel on the uphill climb!

[yorkie_chris]

Er, A*, it's a diesel, they don't have a throttle!

And valves open for longer? Woot? On a petrol engine with carbs, then loads of boot at low revs means the gas speed in the intake tract drops (mass flow still low, pressure rises up to 0 vacuum i.e 1 atm, gas flow is slow), meaning you don't get proper atomisation and you get a slow, innefficient burn.
Also with a carb'd petrol engine, if you have an accelerator pump, then that boot on the throttle will squirt a bit shot of petrol straight in.

Originally Posted by Baph

I've been changing under 2k and running on average around about 2200RPM today (since the conversation). It's a 1.9l engine, so plenty of pull at low revs.

Don't be fooled into thinking that you have to change 'as early as possible'. A labouring engine will use more fuel than a slightly higher revving one.

The best thing you can do to save fuel is to plan ahead. Early observation at junctions, adjusting your speed early so you can time your arrival at junctions/lights etc and avoid stopping if possible. Make sure your tyre pressures are correct, empty your boot, switch off the aircon etc etc etc.

There are so many things you can do but planning is the most effective (shown to save between 10 and 25%) when I've conducted assessment drives.

Don't know what car you've got, I've got a 1.9TDI Octavia and get good mileage out of it, if you accelerate gently and coast to slow down instead of braking later then you should do well.

Something I've been told, though, is to make sure you do give the engine something of a workout. My engine reportedly gets gunge in the turbo (VVT) unless you give it some welly on a regular basis. This amounts to shifting at 3,000rpm where possible (redline is 5k) which generally means I get up to 30mph in 2nd then just shift into third and carry on cruising...

Light throttle control is key to economy.

I.e when pulling away, using mild throttle, but allowing revs to rise it far better than giving it a little beans, but changing at low rpl.

Too low an rpm labours the engine, uses more fuel, cabbies do this requently. Damages the engine and uses more juice so never understand it.

Also, when say your on the motorway, you slow down to 60mph, leave it in 5th/6th, just slightly apply pressure on the throttle and it'll sllloooooowly increase speed, but watch that mpg reader go to over 70mpg

Using the work 1.9 DTi, even though its an estate, i've had 725 miles from a full tank, and regulary see 45-50mpg at 90mph odd... I love it. I hate Dervs, but for road driving you really cannot beat them. Especially as the VXR is lucky to get 300 miles per tank and averages 27mpg on easy driving. The works beast does on average 52mpg. Epic economy.

Mind you, i've had the VXR down to 6.9mpg as well, but no matter how hard i try in the derv, it won't go below 16mpg, even sat on the redline in 2nd