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.