i understand what your saying mate..but MPG is NOT a mesure of distance , look it up on the net, its a mesure of the engines economy in relation to miles covered (ie: not just standing still, which would fall into the same catogary of generators etc)

and a commute to london is pie in the sky...
i live and work in and around London, thats why there is an urban cycle produced for MPG. (london is urban)
the only way your argument would hold water is if you hardly moved at all during your journey, and that would not be motoring would it.

an E60 comes up against the same conditions as a nissan micra, and thats how the MPG figures are calculated...NOT on its "possible" results, but on what it actually gets in real life (london traffic for example)

no figures are given for a clear run up the M1
its combined
urban
and extra urban.

20 mpg for a diesel E60 is diabolical, and something is wrong...either with the car or the driver.

 

miles per gallon has nothing to do with "miles" strangly enough is a measure of fuel used and the miles bit is just for reference, your MPG can be at 0 miles as long as the car/engine is "capable" of moving.
just like horse power has nothing to do with horses

 

Its not worked out that way though in car if it was then as the car stopped the vehicle would stop monitoring fuel used as your not moving. Then once youve moved off look at fuel used again. Every car when stopped in traffic will still be working out fuel burnt and drop your MPG.

 

Let me put this another way, not that I don't think you're getting what I'm saying, I'm just trying to apply it more to the original posters question and this idea that 20 mpg isn't diabolical for a diesel E60. Not for a one-off occasion, or for a regular figure in the same situation.

Two identical cars set off from the same petrol station, both e60 diesels. Through some magic measuring system they know exactly one gallon of fuel has been used and have to stop when it's done so. One of the cars heads out of town and has a pretty easy (even if urban) ride of it. He manages 40 miles and has to stop and record his actual MPG for the trip. He multiplies the number of miles he drove by the number of gallons used (40x1=40mpg). The other car, heads into nasty traffic and uses up exactly half of his gallon of fuel stationary in traffic. No surprise, but after 20 miles he has to stop. He multiples his distance travelled (20) by the number of gallons used (1) and gets (20x1=20mpg). I know that you're saying "but when the car was moving, it was getting 40mpg, and that's the only important thing". If you're talking how cool and efficient an e60 diesel is, then yes that's true. But if you're being asked by that second driver "how come I only got 20mpg?", then the answer is not "oh but really you were getting 40mpg" because that is no use to him. A slightly more useful answer would have been "get BMW's stop/start installed and you'd have got 40mpg for that trip". Again, going back to the OP's question of why he got 20mpg - we don't know if he's in the driver 1 or driver 2 scenario in my example.

Don't know about you, but I'm getting a bit bored of this. We both see each other's point but differ on what truly constitutes an mpg figure.

 

yes it is, when stationary the E60 (diesels anyway) record a MPG figure of + 60 MPG and not 0
the guage shows the needle right over to the left...and 0 is over to the right.

again i stress that MPG is not a measure of distance, how could it be when your car still uses fuel when its not going anywhere, its purely a measure of the engines efficiancy

1 gallon can get you 40 miles along the road...and...
1 gallon can get you 0 miles along the road

you have still used 1 gallon both times but the distance is vastly different, showing you that distance is not the measure, the constant is the "power/output/work/efficiancy of the car/engine and other factors such as drag/wind/friction etc...NOTHING to do with distance.

 

DD how can you get bored of this its great to stimulate your mind (oh and wind each other up as well )
good luck mate.

ps: would/are you happy with a low figure of 20MPG out of the mentioned car, weither its extra urban or motorway???
i know i would not be.
my car has never in its life returned a figure of less than 28MPG and that was when i was driving like a looney through town testing the remap with fast starts and heavy braking

 

It's not great I know, but I average about 9,000 miles a year so doesn't cost me a huge amount. I know I'd get a better figure with a diesel, but the advantages are somewhat eroded by increased taxes. It ends up being only a few hundred quid a year difference.

I was so incredibly close to buying a 535d, you can't believe how close, but somehow on the day, I went for the petrol choice. My next car I might go the other way.

 

Oh, and it was near impossible to find a low mileage 530d or 535d.

 

For what it's worth here's my take on things.....!

I agree that 21 mpg (UK not US) for a diesel is very poor IMHO even 'urban'. The only way I would expect a figure as low as this without there being something wrong is if the OBC was reset and then the car was just sat in nose to tail traffic for a long period of time whithout having the chance to 'be driven'.

MPG in my mind is the amount of fuel a car's engine is consuming - regardless of speed or distance.

Whilst driving the economy gauge records MPG as this is a recognised measure of how much fuel is being used and over a given distance. However, when a vehicle is stationary I believe the way the fuel usage is measured converts from MPG to Gallons per Hour.

Certainly on my wife's car it has a digital read out for both the average and instantaneous (unlike the BMW which as you know is digital for average but a physical gauge for instantaneous). What this does when the car is stationary is converts the readout from MPG to GPH (Gallons Per Hour) which typically reads approx. 0.1 GPH at idle with nothing switched on or 0.2 - 0.3 GPH as items are switched on e.g. headlights, fan blower, heated rear window, air-con etc. (i.e. it increases slightly as load is placed on the engine). However, this instantaneous is included with the overall average fuel consumption figure (acutally measured overall as MPG), because whilst sitting in stationary traffic for long enough the average 'MPG' does begin to decline.

 

Your average mpg has nothing to do with the gauge your on about. That tells you how efficient the engine is at that throttle postion at the actual time(in fact when Audi used the same method it was an efficiency gauge not an mpg one). The simple fact is if you reset the mpg meter and drive 5 miles and get 30mpg that is how efficient the engine has been. Now sit there on tickover for 30 minutes the mpg gauge will go down as you have used more fuel(extra 30 minutes idling) and still only covered 5 miles. This really isnt hard to work out and is very easy to see if you try it if you dont believe anyone.