Diesel mpg - way of driving?

[tjw2007]

As I've mentioned in my previous post, I've been driving a Kia Cee'd 1.6 LS diesel recently (got it as a courtesy car) and I've absolutely loved it. One question though, although I've seen stated in several places that the combined mpg for a 1.6 diesel Cee'd should be 60mpg, I've only been getting around 45-48mpg on average - even though my daily run is mostly on a motorway, which I would have thought would provide better mpg. Is there a good or bad way of driving a diesel where fuel economy is concerned? Is it the case that maybe hitting the higher ranges of the rev counter has an adverse affect on mpg? Any thoughts?

[HDi fun]

Just like any other car really - you'll be very lucky to match manufacturers official figures.

Under-revving is never good - diesel or petrol.

[pgarner]

i just make my figure of 32mpg and thats me living in the country and doing no real urban driving as i can drive right throgh my town in 4th gear, well as long as the only set of traffic lights dont change

[HDi fun]

On board computer thing says I've averaged 38.2 mpg over the last 2500 miles. I reset it on 3rd Jan 2008 (so 2500 miles since then!). That's not bad for a remapped car with 190 plus bhp. It also concurs with my own calcuations. OK, Pug official figures suggest I can do better. But, how accurate are official figures. Or, how how official are accurate figures.

It's down to driving style and methods. I adopt a 'get on with it' approach. I'm sure my Dad could wring 50mpg from it, but it would take years to complete a journey.

[pgarner]

remember official figures are done on a dyno, therefore things as simple as hills are not part of the equation. think about running on a treadmill - last time i was at the gym (about 5 years ago) i could cover 5 miles on the treadmill no prob. yet when i went out running in real life i found that i was getting tired after 3 miles.
also a half of each time is based on accelerating and deceleration where as in real life you hardly ever hold a constant speed in large towns and cities

[Izo Azlion]

I got 55mpg from my Golf, one journey. Bored to high heaven, like, but I did it. I average 35-36mpg, currently.

[tjw2007]

So, does over revving use more fuel or does under revving? Say if you frequently go over 4000rpm - would that use up more fuel than changing gears at 3000rpm? I've never really known how this works.

Cheers

[pgarner]

under revving is where the ecu is kicking in and pumping in more fuel.

yes changing at 4k rather than 3k will use more fuel. but so will under revving as the ecu will kick in and pump more fuel in to save the engine from effectively stalling

as a little test go out and accelerate to 60mph (national speed limit so your not speeding) by changing up at around 3500rpm and take a note of your average then reset it and do it again changing up at 1800 rpm, so your accelerating from around 1200rpm putting the car under strain and see what you get i would say the 1st run would be more economical

[HDi fun]

the days of changing up ASAP are long gone. Years ago you really would reduce engine life if you ever went over 3000rpm.

Those days are gone. Engine design has changed and has moved on.

Fuel usage is affected most by driving style than any other factor in the equation.

Some drivers can wring 40mpg plus from a 4 litre petrol car with automatic transmission.

Others can struggle to see 30mpg from a 1.2 litre supermini.

Neither is wrong. It's just folks and strokes.

[tjw2007]

I was just surprised by the fact that even though I was doing a lot of motorway driving, I still wasn't really getting close to the suggested, combined mpg. I mean, how do they arrive at these figures - do they just drive in a straight line, without over revving or under revving? People go by these figures when considering buying a car, I think it's very misleading.

[HDi fun]

It's not misleading really. Much like womens' clothes sizes. A 16 is always larger than a 14 in the same shop or range of clothes.

But comparing Next to M&S is largely pointless.

Basically, it's a guide. How do you define the average driver? Or journey?

TO a point though, you're right - they do basically drive in straight lines at very stable speeds to get these numbers.

THe only company that seems able to give a good approximation of its official figures on the road it VW (and other VW brands, Audi, Skoda etc.).

[moneypit]

We've a Skoda Octavia hatch 1.9Tdi '04 90bhp chipped to around 120 ish
going to work can get 58mpg coming home 48-50 depending, best was 64mpg to work stuck at 55 were poss just to see, towing c'van when we had it at 90bhp 25 mpg chipped 34 in UK towing in france mostly Mway to site 42! just shows it's not only the right foot but france and the lack of rbouts has always made a difference
on the other hand with the FTO, had it down to 13 mpg but best was 29mpg
'orses for courses!

[billyo]

Plus they dont have all them potholes in the roads. It makes a big difference.

Why do you get better mpg going to work than coming home?

[moneypit]

Cos I dont want to go and why rush to work it'll still be there when you arrive! coming home is obvious!!!!
your right about the potholes hadn't thought about it till you said

[bluemerle]

I took my KIA carens to dealer to have mpg checked they did 100 miles with me in car and returned 49 mpg mainly motorway but never reached more than 60 mph no thanks i'll stay happy with my 35 mpg ha ha

[HDi fun]

MPG figures are hard to equate with real world driving. At least the modern test methods, although they don't give anything like realistic numbers, are repeatable.

A car with a combined figure of 29mpg will be more thirsty that a car with a combined figure of 39mpg.

Neither will achieve the the exact figures but at least the test method is the same.

Years ago manufacturers used to lean off the mixture at the exact RPM that coincided with 56mph in 5th gear so that the numbers on the dyno were incredible.

Cavalier 2.0 SRi 130 and 58mpg - nope, not a chance.

[Yugguy]

My Bora 130 is chipped to 170/290, and I am averaging 53.1mpg, I have a hilly 25 mile cross country drive to work, which a few bits that I can cruise in.

[HDi fun]

Originally Posted by Yugguy

My Bora 130 is chipped to 170/290, and I am averaging 53.1mpg, I have a hilly 25 mile cross country drive to work, which a few bits that I can cruise in.

Those PD engines are capable of incredible fuel economy. The fuel pressure in the individual injectors is massive - higher than any current common rail diesel. 53.1mpg is still high, even for one of those. Is this a measured and verified figure?

I'm not totally surprised to be honest though, much as PSA/Ford seems to have made the near silent 4 cylinder diesel, VAG has made the true reason for having one in the first place ie. massive miles for each litre delivered to the tank.

[pgarner]

no Hdi 53 could be about right. sound like a tractor but you do get incredible mileage outa them. and not bad for servicing as well. shame the injectors cost a fair amount when they go

[HDi fun]

I've never driven a PD for long enough to make a quantitive assessment of the long term fuel economy but in fairness over 50mpg is written about quite frequently.

The 4 cylinder units can be a bit rough - the earlier TDi models were smoother (eg. the TDi 110).

[Yugguy]

I haven't done the sums for my mpg no, I'm just taking it off the computer.

I have to say it's quite noisy tho, on throttle anyway, I know it's a 100k+ engine, but the missus' focus tdci is so much quieter.

Diesels are becoming amazing tho, Jag's new XF 3.0 V6 diesel will do 0-60 in 6.4s and still return 42mpg and only 179gms of CO. You can't argue with figures like that.

[HDi fun]

The PDs wer much better as V6 engines - the fours were a little bit vocal at times.

That's why I was so fond of the 2.2HDi I USED to have

[WLBjork]

Just been toScotland for 3 days. Averaged 49MPG for the whole trip using the 2.0 CR TDi of VAG.

Given the engine still needs running in to optimum (only broke 4K on the trip), and there were two extra adults and a whole bunch of luggage being transported and add in that I wasn't driving particularly economically (if speed limit was 70mph I was travelling at 70mph), returning a figure just below the combined value is - IMO - pretty good going.

[HDi fun]

It is indeed. 49mpg is not to be sniffed at.
My 2.2 HDi Peugeot 406 offered a long term 37-38 according to the computer. Lot's of my journeys got shorter over the last couple of years so not real complaints as such. And the longer journeys I used to occupy the RH lane most of the time, speeds not to too far adrift of three figures.

I suspect that the 192bhp (and 320lbft) remap did not cause much difference. I DO suspect, however, that my inclination to use it, did so

Still - try and find a petrol car with that kind of mid-range (and high end) acceleration that could even better 20mpg driven similarly.

It was quick, and smooth without a doubt. It could knock off 30-60mph in about four seconds in 3rd gear so we're talking strong acceleration here.

Now, sadly, it's been smashed up thanks to an idiot who emerged from a T junction right across me (on a de-restricted road) whilst I was doing about 60mph.

Thankfully minimal injuries only - just two piles of very expensive bent metal and plastic.

[WLBjork]

That 49 (49.12 to be precise) is from the calculator on this site - the computerised figure is 52.2, meaning about 6% inaccurate.