'Petrol efficiency experiment; an increase of 20%' blog discussion

John_Pierpoint · 16 January 2008 at 3:14AM

According to Germany's Federal Highway Research Institute (BASt), using dipped headlights increases fuel consumption by three per cent, while LED lights reduces that to 0.3 per cent.[In Scandinavia it is mandatory to drive with your headlights on and the EU wants to make it mandatory throughout the union]

If you have cruise control use it.

Slip streaming a lorry makes a big difference BUT you may arrive in the next world early, if you stop paying attention!

Attend to tyre pressures.

Small cars thrashed really gulp juice.

VirtualMusician · 16 January 2008 at 8:39AM

Hi Folks,

I don't know if anyone else as noticed this but I drive an automatic and if you lift your foot from the acc pedal slightly, the revs drop but you still matinain the same speed. It's quite amazing how much you can get the revs to drop before slowing down.

Also, when my wife accelerates, she puts her foot half way down instead of gradually putting her foot down so, the car is using fuel reving to try and be quicker than it can be.

ahall41116 · 16 January 2008 at 10:07AM

at last i am not the only one doing this!

my last car (3 yr old passat 1.9 dci) i could get an average of 49 mpg on motorways, 46 mpg urban driving, and i would be constantly taking my foot off the accelerator when going downhill, to keep fuel efficiency high.

i now have a passat 2l tdi and am struggling to get 43 mpg onmotorways, 38mpg urban driving.

i do over a 1000 miles a week, and its killing me!!

ash

craptiger · 16 January 2008 at 10:38AM

Hi,
I have a very large silver trophy in my house which was won by my great uncle in 1953, in a competition organised by Shell Oil to see who could drive furthest across the desert on one tank of fuel.
He won in a very large Jaguar, and his technique was to drive as fast as possible, then turn the engine off and coast, then drive as fast as possible, then coast etc etc. Would be interesting to see how that compares with doing 56mph constantly eh?! Sadly this doesn't work in my current modern car because as soon as I switch the engine off the steering and brakes go - oops!

harryhound · 16 January 2008 at 10:55AM

redux wrote: »

Errrm, a slight mathematical difference about what Martin said:

Going 20% further on a tankful means the rate of consumption, and hence the cost of a fixed length trip or of all fuel bought, drops by 16.7% not 20%

To make the point clearer by stretching things, going 100% further on a tankful is a 50% cost saving

Very good point Redux.
"Figures don't lie, but liars sure can figure" is a bit of wisdom from USA.
As we own metal boxes with engines to go places out of the wind and the weather, litres per 100 KM makes much more sense. I bet it is the car industry that favours the car centred measure of miles per gallon.
If Martin had done one leg of his journey by bike, he would find he had made an "infinity" percentage improvement in his miles per gallon (and get fitter too:D), while reducing his costs by 100%.

Similarly, those people pointing out that the on board computer is set inaccurately are largely missing the point, the relative improvement is probably accurate even if the measurements are somewhat inaccurate.
100 + 25% = 125 whatever the unit of measurement is; and
125 - 20% = 100.
Always do the calculation the other way round, when a silver tongued salesman is blathering on about "savings". Usually they are just working from a script, don't really understand and you can really unsettle them;).

Wickwarrior_2 · 16 January 2008 at 10:59AM

A few years ago I got a car with a trip computer. I checked it by always filling up at the same pump - using the autostop mechanism. I then checked my usage against what the onboard systen said - it was very accurate.

I used to regularly drive up and down the M4 (I worked in Swindon) and found the best way to get increased ecomony is to drive about 3 or 4 car lengths behind an artic in the low pressure zone behind them. They do a fairly regular 60 miles per hour. I never got less than 68 miles per gallon - I drive a 1.9 turbodiesel Skoda. Using cruise control gave me less. I also found that the journey only took 5 minutes longer. After a while I found myself trying to get higher and higher milages and the best I ever achieved was 75 mpg from Bristol to Swindon.

I found using the 'ongoing' mpg screen of the onboard computer meant I learned to be very light on the throttle - and what would I have done with the extra 5 minutes anyway.

Good article

cabbageboy · 16 January 2008 at 11:08AM

To pick up on a comment in Martins experiment:

"The two main ways of doing this are when coming to a junction; rather than just braking I let the car slow down more naturally,"

Did you realise, that Modern, Computer controlled Injection Engines use NO FUEL AT ALL in this situation?

If you slow down, foot off the acceleraor, the Management system sends NO fuel to the engine - the momentum of the vehicle keeps the engine running.
Therefore, slowing gently means FREE miles!

Rather than keeping the foot on the Gas, then slamming on the brakes coming to a junction, LOOK AHEAD, and slow gently.
Although, don't push the clutch down, as this means the car's momentum is disconnected from the engine, and the management system will need to use fuel to keep the engine running!

For those of you interested, the ADVANCED DRIVING system teaches you this methond of driving style, with anticipation and forward looking key to both safe and econimical driving...

Check out http://www.iam.org.uk/ for details....

It's worth thinking about - Imagine if on the 6 o'clock news tonight, they anounced that BP were reducing the price of Petrol by 20%!! - You wouldn't be able to get NEAR a BP filling station...
Now, you have the chance to do it yourself!

setmefree2 · 16 January 2008 at 11:10AM

Hi

Me & Mr SMF are trying really hard not to use our car at all. We have a Scenic. The problem with this is that often the battery goes flat through lack of use and we are continually having to recharge it. We have bought a solar pannel which tries to get it "juiced up" but does anyone have any other ideas or share our problem We can't live without a car completely.:rolleyes:

cabbageboy · 16 January 2008 at 11:16AM

Hi SMF...

How long does it go between uses - your scenic??

It should be able to stand for a few months without the battery going flat...

If you really only use it a couple of times a year, isn't there a cheaper alternative to owning a car, paying insurance, MOT, tax etc??

Just wondering what time you're talking between uses - maybe there's a fault that's draining the battery??

harryhound · 16 January 2008 at 11:19AM

craptiger wrote: »

Hi,
I have a very large silver trophy in my house which was won by my great uncle in 1953, in a competition organised by Shell Oil to see who could drive furthest across the desert on one tank of fuel.
He won in a very large Jaguar, and his technique was to drive as fast as possible, then turn the engine off and coast, then drive as fast as possible, then coast etc etc. Would be interesting to see how that compares with doing 56mph constantly eh?! Sadly this doesn't work in my current modern car because as soon as I switch the engine off the steering and brakes go - oops!

A couple of years ago I used to drive an diesel Vectra Estate (company car). In the handbook it said something like "Do not freewheel down hills, this will give you worse MPG, as the engine management system shuts off the fuel input to the engine automatically" and as you say, when the engine stops going round the brakes and steering suffer.

I used to regularly drive up and down the M4 (I worked in Swindon) and found the best way to get increased economy is to drive about 3 or 4 car lengths behind an artic in the low pressure zone behind them.

I would like to thank the driver on the A2/M2 who allowed me to do this trick on sidelights for over 60 miles, when the alternator on my mother's aged Fiesta wore out its brushes in the early hours. It probably unsettled him almost as much as us, 'cos we were worried about running out of both petrol and electricity, but we made it home:T

'Petrol efficiency experiment; an increase of 20%' blog discussion

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