Misleading MPG figures from MB?

[Rory]

Now, having driven it for four weeks and what I reckon to be a really sedate pace and managing no more than 34mpg on selected motorway runs at a steady 60-70 mph, I was amazed that the dealer claimed they obtained 47mpg on the run. I am going to drive the same route myself tonight, in Eco mode and at a sedate pace to see what "my slowest driving style" will return on the same route.

One thing I would say is don't spend too long getting up to cruising speed and then back off the gas as much as you can.

Sorry if this is teaching you to suck eggs, but one of the big things with diesels is to let speed decay off on the over-run without braking, and to try and carry speed wherever sensibly possible.

 

[rf065]

I think you just get some cars that don't do well with consumption, where as the same model sat next to it does brilliantly.

Probably more to do with the driving style rather than the car though. It's usually the human element that needs fixed.

Russ

 

[exjag]

One thing I would say is don't spend too long getting up to cruising speed and then back off the gas as much as you can.

Sorry if this is teaching you to suck eggs, but one of the big things with diesels is to let speed decay off on the over-run without braking, and to try and carry speed wherever sensibly possible.

Not sure what you're saying here.

Accelerator control is important for both economy and safety. Quoting the book 'Roadcraft', the police driver's manual (which I have had the good fortune to have had drilled into me since I began motorcycling and driving police vehicles at the ages of 16 and 17 respectively) :-

"Good acceleration sense requires careful observation, full anticipation, sound judgement of speed and distance, driving experience and an awareness of a particular vehicle's capabilities. A lack of acceleration sense causes many common mistakes: for example accelerating hard away from a junction and then having to brake sharply to slow to the speed of the vehicle in front; or accelerating to move up behind a slower moving vehicle and then having to brake before overtaking. If you have good acceleration sense you are able to avoid unnecessary braking."

You see these mistakes happening time and again. I was always taught that if you if you make the mistakes outlined above, and others similar, and have to brake, you've wasted the fuel you have used in accelerating. One important principle is distance between your vehicle and the vehicle in front. In stop - go traffic for example, if the distance is reasonable you can control the movement of your vehicle using only acceleration and deceleration; braking is largely unnecessary. Next time you're in a line of traffic, look at the bloke in front who's constantly braking because he's right up the exhaust of the vehicle in front of him - he's using far more fuel than he needs to.

 

[gizze]

Probably more to do with the driving style rather than the car though. It's usually the human element that needs fixed.

Russ

I'm not so sure, I have been in the same model a couple of times where the consumption is far different.

I know the guy at Mercedes has said that with the E350cdi they have had on their demo fleet that some are returning nearly 40 mpg and the same car in a different colour is struggling to hit 34mpg.

These are cars they are taking home with them for a week at a time.

The fact you can adjust the fuel ratio on the injectors etc. can probably make the 20% difference alone.

 

[grmc]

Accelerator control is important for both economy and safety. Quoting the book 'Roadcraft', the police driver's manual (which I have had the good fortune to have had drilled into me since I began motorcycling and driving police vehicles at the ages of 16 and 17 respectively) :-

I know what you mean here exjag - as a former police officer I've had the same/similar training too, back in the 80s and have used them ever since. Roadcraft is superb technique to be taught when young, particularly as I am also a motorcyclist (more recently I taught CBT and Advanced Intros and all of the techniques provide enlightenment to new and experienced riders alike).

I would never claim to be the best driver in the world, but I think with the methods I've been taught and my own experience that I can claim to be of above average ability, so I'm fairly confident that the poor figures I'm seeing are not due to any erratic driving style.

 

[Rory]

Not sure what you're saying here.

I was saying pretty the same as you quoted from Roadcraft.

The Police way of driving isn't particularly the best for economy though. They don't believe in letting speed decay off (during which time fuel is shut off and you're moving along at no cost).

Their style is more "gears to go, brakes to slow" - it's a much more positive style of driving and if you drive a diesel auto in any way forcefully it'll murder the MPG.

 

[roop_the_loop]

I'm not so sure, I have been in the same model a couple of times where the consumption is far different.

I know the guy at Mercedes has said that with the E350cdi they have had on their demo fleet that some are returning nearly 40 mpg and the same car in a different colour is struggling to hit 34mpg.

These are cars they are taking home with them for a week at a time.

The fact you can adjust the fuel ratio on the injectors etc. can probably make the 20% difference alone.

I agree that no two cars are ever completely identical. They're set up differently, the tyres may be different, everything from engine oil to air filters will be in a different condition, etc., but I would still put those under the heading of 'human' rather than 'vehicle' differences. If you genuinely build two identical vehicles, set them up the same, maintain them the same, and generally remove all the variables you can, and then do side-by-side comparison of fuel consumption I'm sure they will be fairly close to (but probable still not 100% the same as) each other.

Most of the difference in one car's fuel economy and another (seemingly identical) one's, probably comes down to the human and/or external factors. So when a car salesman takes home a E350CDI one week and gets 40 mpg, and takes another E350CDI next week and gets 35, I'm pretty sure it has less to do with the difference between the cars, and much more to do with how he used it, what the traffic conditions were like, even the weather and temperature. But we tend to overlook all that and say 'this week I have a different car and I get different fuel consumption figures, therefore it must be the car that is different'.

 

[Frontstep]

Aah the obsession with MPG,
I think a depreciation gauge centred large in the dash and indicated in -£ per hour would be more apposite

 

[geraldrobins]

I dont think MB have a case to answer. According to 'Honest John', on average cars achieve 87% of the quoted combined mpg. MB on average achieve 85% which is near the average. Some MBs better the quoted figures. Also if you look at the 'What Car' data
some MBs better Audi and Ford.
Its all about driving style, speed,types of road, inclines and especially ambient temperature especially on relatively short runs. In my opinion of course.

 

[television]

I am never bothered about fuel consumption, as its a good way to get rid of surplus money, but on the way home from the meet on mainly B roads I noticed the CL500 was showing 28mpg, for the next 75 miles I tried in vain to get the 30 up, and failed at 29.9, the car is supposed to do 32, I could beat the quoted figures in the SL, buy not this one so far.

 

[roop_the_loop]

I'm not obsessed with fuel economy, otherwise I'd be driving a Nissan Micra or similar, not an E-class Merc. However, I would appreciate being told the truth, which the official figures plainly aren't. I think that there's something majorly wrong with an officially sanctioned system where the authorities pretend to regulate the fuel economy figures, but don't, and manufacturers run coach and horses through the loopholes, and then some (surprisingly many, judging by this forum) people are happy to shrug it off as 'everyone knows the figures are BS' as if that makes it OK.

 

[L John]

Surely I'm not the only one to beat the official mpg
C350 elegance 2008
Official stats...
Urban mpg 19.9 mpg
Extra Urban mpg 38.2 mpg
Average mpg 28.5 mpg

I got 41.2mpg on a 47 mile run on my economy test and generally get 25 to 30mpg on short trips of 10 to 20 miles from cold start.

 

[roop_the_loop]

Surely I'm not the only one to beat the official mpg
C350 elegance 2008
Official stats...
Urban mpg 19.9 mpg
Extra Urban mpg 38.2 mpg
Average mpg 28.5 mpg

I got 41.2mpg on a 47 mile run on my economy test and generally get 25 to 30mpg on short trips of 10 to 20 miles from cold start.

Kudos on that. But can you sustain the 41.2 for, say, a month or even just a few days? After all, the official 'combined' figure shouldn't represent just the best-ever run you might get once in a lifetime, downhill on a light load and over-inflated tyres with the wind behind you.

I also once got 57-ish mpg for the first 20 miles of a 40-mile run. By the time I got back, the average for the whole trip had fallen to the low 40s. (I put the initial 57 down to some measurement or calculation error by the system.) My average for the past ten months / 20k miles is 43.5, hence despite the (very rare) occasional 50+ figure I feel in real terms I'm still well short of the 53.3 mpg official figure.

 

[L John]

Kudos on that. But can you sustain the 41.2 for, say, a month or even just a few days?

I'd say yes if I did runs of 50 miles of more at a time and had a clear road where cruise could be set at 55 for over 90% of the run with almost no need for braking.

It was a test to see what is possible. Everything that knocks MPG from that figure is down to the journeys distance, driving style, other traffic and cruising speed.

Roads are busier than when these official tests were designed and that's a significant factor in my opinion.

 

[television]

If the fuel consumption was my main worry, it would spoil every drive. to have to drive thinking about the consumption must be horrible..

It is the difference after all, and unless you are driving 50k miles per year, it is only a tiny difference in cost. At this rate you may as well add the tyres into this equation, some cars go 10k miles on a set while some others will go 30k, and the difference in cost is 10 times more than the difference in fuel consumption.

 

[gizze]

I'm not obsessed with fuel economy, otherwise I'd be driving a Nissan Micra or similar, not an E-class Merc. However, I would appreciate being told the truth, which the official figures plainly aren't. I think that there's something majorly wrong with an officially sanctioned system where the authorities pretend to regulate the fuel economy figures, but don't, and manufacturers run coach and horses through the loopholes, and then some (surprisingly many, judging by this forum) people are happy to shrug it off as 'everyone knows the figures are BS' as if that makes it OK.

But I can get the official figures in every car I have been in.
But then I understand what the test is.
It seems you want to get the official figures not replicating the test?

 

[gizze]

I will admit that being in an ML with no OBC is nice though.

 

[gizze]

Surely I'm not the only one to beat the official mpg
C350 elegance 2008
Official stats...
Urban mpg 19.9 mpg
Extra Urban mpg 38.2 mpg
Average mpg 28.5 mpg

I got 41.2mpg on a 47 mile run on my economy test and generally get 25 to 30mpg on short trips of 10 to 20 miles from cold start.

Petrol?

Petrol cars will always get closer to the official figures as they get to temperature quicker.
With a diesel you sometimes have to drive for 30 minutes before you can start to see the extra urban figure, which also means you have to drive for 30 minutes before you can see the combined too.

Only got to add a few sub 30 minute drives in each month to knock your average right down on a diesel.


I had an A6 3.2 petrol and was lent the 3.0tdi for a week while they replaced my nav system, and I got worse mpg on my 10 mile 25 minute commute in the tdi than the petrol. It just didn't get to temperature.

 

[L John]

If the fuel consumption was my main worry, it would spoil every drive. to have to drive thinking about the consumption must be horrible..

Agreed, I only did the test because of the on board stats, never bothered to check mpg on other cars or bikes :lol:

Petrol?

Yes mate, another good post

 

[television]

Petrol?

Petrol cars will always get closer to the official figures as they get to temperature quicker.
With a diesel you sometimes have to drive for 30 minutes before you can start to see the extra urban figure, which also means you have to drive for 30 minutes before you can see the combined too.

Only got to add a few sub 30 minute drives in each month to knock your average right down on a diesel.


I had an A6 3.2 petrol and was lent the 3.0tdi for a week while they replaced my nav system, and I got worse mpg on my 10 mile 25 minute commute in the tdi than the petrol. It just didn't get to temperature.

After 1.3 miles my CL500 was up to 80c this morning and the car was out all night , it was doing 22.9 mpg at that point in time