Dr Dave

thats rubbish...go look at your car it even says MPG on it it does not say efficiency guage on it?

your second paragraph is rubbish also, reseting the "mpg computer" just gives you "instant" as palmo so very well explained.

Jambers

MPG = Miles per Gallon...

the clue is there - it is a measure of distance (miles) and fuel consumed (per Gallon)

Dr Dave

so horse power is to do with horses?
and brake horse power is to do with your brakes?

MPG is not a measure of distance, just google it.
you can be stationary and still record a MPG figure for your car...go figure.

are there brain doners??

Dr Dave

ok, even "WIKAPEDIA" says MPG is a measure of fuel economy and comsumption


NOT distance, please let it rest there its fact and to argue it is belittling to your inteligence.



One should note that MPG works differently than litres per hundred kilometres. l/100km denotes a rate of fuel consumption, while MPG is a measure of fuel economy (or 'gas mileage'). If a car uses less fuel, the MPG increases, and l/100km decreases, but the percentages will not match, because the values are reciprocal.

For example, 20% better mileage does not mean 20%, but 16.7% less fuel. This comes from the following calculation: 20% is 1.2 times bigger distance, therefore 100% / 1.2 = 83.3% of the original fuel consumption, or 16.7% less fuel.

If a driver who travels 15,000 miles a year switches from a vehicle with 10 mpg to 12 mpg average fuel economy (0.10 gallons per mile to 0.083 gallons per mile), 250 gallons are saved. A similar 20% improvement in exchanging a 30 mpg for a 36 mpg (0.033 gallons per mile for 0.27) vehicle saves only 83 gallons for similar driving patterns.

Since l/100km is linear instead of reciprocal, a driver who travels 15,000 km a year and switches from a vehicle with 20 l/100km to one with 19 l/100km has the same 150 l/year savings as someone who switches from 5 l/100km to 4 l/100km.

DD_545i

I googled it - "Miles per gallon (MPG) is a standard unit ~ that measures how many miles a vehicle can travel on one gallon of fuel.".
http://en.wikipedia.org/wiki/Miles_per_gallon

Dr Dave

you googled it but you didnt read it
look at the paragraph i posted from your own "google" it clearly states "One should note that MPG works differently than litres per hundred kilometres. l/100km denotes a rate of fuel consumption, while MPG is a measure of fuel economy (or 'gas mileage'). If a car uses less fuel, the MPG increases, and l/100km decreases, but the percentages will not match, because the values are reciprocal"

and horse power has nothing to do with horses per sei .read the explanation
its to do with power exerted and a horse was used to explain the concept. ..they could have used an elephant , and then i would have had a 3 Elephant power car. good job he didnt use chickens

Phantom Mark

lmao, 500 hundred elephant powers....the mind boggles now

Palmo

OK - from the comments on the last few pages (and I haven't read back beyond that point) I'm with Dr Dave on this one.

MPG is used as a measure of how much fuel is being used but does not have to denote a distance or particular speed.

Take an example, if a car travels at 30mph doing 30mpg, in 1 hour it will in theory use 1 gallon of fuel (of course in reality to do this it would have to be doing an average of 30 mph to achieve this).

However, if the car is stationary for an hour idling, whilst it 'technically' it is doing 0 mpg due to being stationary, it is in fact using less fuel that if it were being driven - typically 0.1 - 0.3 Gallon per Hour, whereas it would be using 1 gallon being driven, therefore the measure - MPG - goes up as less fuel is being consumed!

The bottom line here is that the term MPG is used as a recognised means to measure how much fuel an engine is using. To say a stationary car is doing 0mpg is therefore inaccurate and misleading IMHO.

Dandle

If that was correct my car could sit in the filling station use all its fuel and record over 60 mpg then without ever turning a wheel.

Palmo

But the very fact that the engine is using only 10 - 30% as much fuel while at idle for the same duration (1 hour) means the engine isn't using as much fuel which is the point I'm making. If the car isn't using as much fuel the "economy" has increased i.e. the vehicle is using less fuel.

I still think saying 0 MPG is misleading as the term MPG is simply used as a term of measurement - just my opinion! As I said in a previous post " 'technically' it is doing 0 mpg due to being stationary" but only if you take the word's literally.

Anyway.....back to OP question I still think 21 MPG is dreadful for a BMW diesel. I live on the outskirts of Manchester which is one of the queuing capitals of the country! Granted the majority of my mileage does end up being combined rather than soley urban, but I know when I trip my OBC (which I do every time I fill up) followed by queuing in traffic I immediately get way better than 21mpg after the wheels have turned for a few hundred yards. It then only takes the smallest amount of driving and the economy shoots way up. I understand the pre-LCI 525d and auto in particular cannot match the LCI's but I still think this is too low.

By contrast I recently drove round a famous 13 mile "toll road" - did about 6 laps in total (not consecutive). I tripped the OBC before each lap, and during my hardest lap returned 22 MPG - by far the lowest the car has ever returned, but to be expected (normal driving never see's much below 40MPG - certainly never below 38 MPG). Speaking to others - who were predominantly in petrol cars, a good average was around 11-13 MPG. The journey from the UK and returning averaged 51 MPG whilst cruising @ around 70mph inc. an autobahn blast to 149mph (width of needle from 150mph).