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

shawad wrote: »

Regarding the debate on 56MPH earlier in this thread. This figure is quoted everywhere as it converts to (near enough) 90KPH, which is the speed limit in most of europe for outside built up areas. That's the only reason it's used, not wind resistance, not because it's a magic number for the efficiency of internal combustion engines.

75MPH figures are also quoted since that's 120KPH and that used to be the limit in most European countries for motorways.

I read my Golf manual last night and for my 1.4 engine it reccomends 58 mph as the most efficient top speed.

pault123 wrote: »

I used to get on average 325 miles per 45litres. I'm going to do no more than 60 on the motorway and change gears everytime my revs hits 2000. Will also try the 2000 rev take off from stop.

Something I thought about tonight when changing up as soon as possible, would it be counter productive to change up a few seconds too early where you hear the engine labour slightly like you should have waited a few more seconds? i'm thinking a labouring engine will use more fuel. So there can be such a thing as changing up too soon.

Modern turbo-diesel engines have an optimum rev range for fuel consumption - they use such significant boost that they are actually less efficient at lower revs. The actual range varies from car to car, but on my Micra it was anything over 2250 revs - any lower and it would be uncomfortable. Most manufacturers set their cars to run in this range at cruising speeds (i.e. 50-70mph), so all you need to do is to find the revs at 50mph, and only change up when you'll be in the rev band in the higher gear.

With petrol engines it is slightly different, as they have a throttle, which physically blocks the airways into the engine. It is better to have the throttle open more when accelerating, so changing up at low revs should increase economy. However, with variable valve timing and so on, you may not notice a significant difference. Try it and see. One thing to remember is that petrol engines seem to perform better when they are occasionally thrashed (an "Italian Tune-Up", as my Dad used to call it). It seems to clear things up a bit, especially if you use one of those injector cleaners. Only do it when the car is fully warmed up (at least 10 miles) - it only needs to be done once in a while.

On another point, people have mentioned using bikes or Shank's Pony for short journeys. It's not just a green idea: most of the wear in a car engine is when it is cold. So you are using much more fuel to keep a cold engine running (with poor economy). AND you're wearing the engine out until the car is warmed through:eek: (again, at least 10 miles). Nothing kills a car more than lots of short journeys. So taking kids on a short journey to and from school is the worst thing for car (apart from the speed humps, but that's another discussion :mad:;) )

LYNNIT wrote: »

I seen a product in the garage called Redex which is reputed to save up to 20% of petrol when it is put in the tank.
Does anyone know if this stuff works?

Lynne.

No, it does virtually nothing.


Regarding anticipation, one day when it was foggy I realised why so many people make such a meal out of driving smoothly. In the fog visibility was reduced to the couple of 10s of metres in front of the car, so corners were a surprise as were any other events. On a clear day I'll look a good way into the distant, working out what might be happening and planning ahead. In a slow van on the motorway I managed from Manchester to Bristol without having to brake or accelerate at any point, all by planning ahead.
Anyway, the reason that so many people seem to drive in a jerky and braindead fashion must be because they stare at the 100m of road in front of them rather than looking at the whole picture.

Personally I value my time as being worth a certain amount, so tend to travel at 85 indicated on motorways and I will take scenic A/B roads for fun if I'm in the right mood and there's not too much traffic around. On a long run it's amazing how good economy can be even if getting on with things, because a smooth style is efficient.

ILoveSaving wrote: »

Hi Martin
I'm definitely going to try your petrol experiment. Just thought you might like to her about mine.

Back in October last year I had just filled up as usual, which was every 2 weeks on the dot. So I wondered if by leaving my radio off for the following 2 weeks, would there be any difference in my petrol consumption? I listen to the radio all day at work any way, so I thought I could go without for a while till I got there.

To my surprise, doing exactly the same trips as I usually do, including school runs, dance classes, shopping and work etc. I did not have to fill up for 3 weeks! No one thought this was possible, as my dad said that the radio should run on the battery not the petrol. I don;t know I'm not a mechanic. So I did it again.

Another 3 weeks went by before I had to fill up, then again and I've done it ever since. I dare not put the radio back on now. It's saving me so much. I don't know if I have a fault with my car? Our mechanic had never heard the likes of it before. Or maybe its just the type I drive which is a little old faithful Nissan Micra.

But why don't other people try in other types of car and see what happens? Its worth ago for the savings I'm making. :rolleyes:

The radio doesn,t run on petrol:rolleyes:.Not quite.
The car battery isn,t like the batteries we use in the TV remote etc,its more of a storage unit,a rechargeable battery.It needs to be fully charged to start the motor,thereafter it is continually re-charging while you drive.Everything electric in the car runs off the battery,air con,elec windows and your radio.The petrol powers the alternator which recharges the battery.The more electric stuff you have on in the car,the faster the battery power will be used up and the harder the alternator will have to work to keep the battery charged up.So yes, the more electrical bits you have on in the car the more petrol you will use.You will probably notice that you get more mileage out of a tank in the summer also as you are not having to drive with the headlights on all the time.
I noted that you said your mechanic couldn,t understand how you used less fuel with the radio off.A mechanic should know this so I would switch mechanics if I were you.;)

shelovestobuystuff wrote: »

The radio doesn,t run on petrol:rolleyes:.Not quite.
The car battery isn,t like the batteries we use in the TV remote etc,its more of a storage unit,a rechargeable battery.It needs to be fully charged to start the motor,thereafter it is continually re-charging while you drive.Everything electric in the car runs off the battery,air con,elec windows and your radio.The petrol powers the alternator which recharges the battery.The more electric stuff you have on in the car,the faster the battery power will be used up and the harder the alternator will have to work to keep the battery charged up.So yes, the more electrical bits you have on in the car the more petrol you will use.You will probably notice that you get more mileage out of a tank in the summer also as you are not having to drive with the headlights on all the time.
I noted that you said your mechanic couldn,t understand how you used less fuel with the radio off.A mechanic should know this so I would switch mechanics if I were you.;)

Surely were talking 0.5% fuel saving when talking about not having your radio on and your headlights on in the winter? I would hate to turn my radio off and I like having my headlights on when its dull and rainy, there must be a point where were taking saving fuel a bit too far

*edit* busabus's post is exactly what I was getting at 50% saving from no radio seems ridiculous. Its such a low drain appliance vs revs, and driving flow on petrol consumption.