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

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

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This is the discussion to link on the back of Martin's 'Petrol efficiency experiment; an increase of 20%' blog. Please read the blog first, as this discussion follows it.
For full info on cutting the cost of driving, read the
Cheapest Petrol and Diesel article.
Click reply to discuss below.
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  • Good trial, Martin, and no doubt you saved petrol, but how much? The onboard computer in cars is not reliable and especially so when you are measuring each trip separately. A better way but a little bit more work is what I have been using over many years.
    First start with a full tank; this is not difficult as the cut out on most pumps uses the pressure from your tank. Record mileage at start and again when you next fill up. Using the recorded difference in mileage and the amount of petrol needed to refill the tank it is easy to calculate the mpg. Every time I do this it differs from the computer average. Having tried this on many cars over the years I have always found my method reliable and the computer rarely agrees.
    Another check on the onboard computer is to wait until it flags up the warning: only X miles of petrol left. Try driving those X miles to see what happens (you may need to carry a spare can of petrol!) . :eek:
  • hi martin, i too am currently doing the same experiment. i drive a renault clio 1.2 and it is fairly ecconomical. i reset the fuel consumtion on the dashboard computer every day and watch it as im driving around and was amazed when on the motorway that if i cut my speed by 10 mph the fuel consumption changed drastically. and like you said it dosnt take you any longer to get to your destination either. im also currently shopping around for the cheapest petrol at the moment as my car is by far my biggest monthly outgoing.


    :money:
  • i only just found the setting on my car for telling me the average MPG - it's a little car and my current average is 39.4..... and i think it should be better than that. i can't seem to reset it by trip yet (i will get out the manual this weekend though after reading the blog). i'm definitely watching the way i drive though - anything that saves petrol costs at the moment is a great idea!
    :happyhear
  • wyzewyze Forumite
    23 posts
    My trip computer is broken but I use the one on this website which remembers past results and is handy for comparison. http://www.torquecars.com/tools/uk-mpg-calculator.php
  • anewmananewman Forumite
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    llandaff wrote: »
    First start with a full tank; this is not difficult as the cut out on most pumps uses the pressure from your tank.

    I think different pumps use different cut off levels and it also depends on other things like temperature of the tank (with heat liquid expands) and probably also how level the car is as this will affect the level the petrol comes up to at the bit you fill up at. Anyone with an older car that has a petrol guage designed without a stabiliser will see the effect of this when going around corners (suddenly more petrol, then less petrol, then more).

    While not scientifically precise I think it is the best approach. I would assume the onboard computers base the calculation on how much petrol flows through the injectors so should be a good estimate, if not precise and perfect.
  • indierocker85indierocker85 Forumite
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    Was sat at Shell today and staring at the price and thinking, How much longer will I keep my car? As I have a moderate income but the price of petrol os ridiculous, I currently drive a 1.3 fiesta, and I have just read the article on petrol. Sainsburys is always the cheapest and closest for me, plus i can collect nectar points as well.

    I am planning to try the following, filling up my tank and driving as normal and seeing how many miles I get from a full tank of 40 litres.When this is done and I work out my average MPG, I am going to completely declutter the car, check the tyre pressures are spot on and drive as martin as suggested to see what the difference is between the two MPG averages. I am sure the results will shock me

    It's interesting to think, what could we as drivers and tax payers realistically do to try and bring down the cost of petrol? Protests? Boycotts?

    Also where I live the most expensive station is at 112.9 for Unleaded (BP) and the cheapest is 103.9 (sainsburys), the two stations are literally about 200 yards apart yet bizarely people still go to the BP garage effectively wasting 9p a litre.

    If I can't save by trying the above, I'm afraid I'll ditch the car and adapt the money saving train commute again
    Live for what tomorrow has to bring, not what yesterday has taken away
  • anewmananewman Forumite
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    I am planning to try the following, filling up my tank and driving as normal and seeing how many miles I get from a full tank of 40 litres.When this is done and I work out my average MPG, I am going to completely declutter the car, check the tyre pressures are spot on and drive as martin as suggested to see what the difference is between the two MPG averages. I am sure the results will shock me

    Just to say maintaining tyre pressures is a safety issue and if found to have under-inflated tyres you can be fined and get points from the police. Under-inflated tyres will also wear differently and be more likely to need replacement quickly. Also, forget the filling station air. It's usually inaccurate and when you've driven there your tyres are warm anyway which affects the reading.

    I believe biggest improvements can be gained from maintaining/servicing the car properly and as often as needed, and also driving at the speed quoted by your car manufacturer as having the best MPG, usually about 56mph, instead of 70 or 80mph on the motorway. The faster you drive, the less fuel efficient your car will be over the distance you travel. Sitting at 56 you can also stick in the inside lane unless other people really are travelling slower, and you therefore are at less risk of accidents too. Sitting behind the lorries can also benefit fuel efficiency in terms of aerodynamics too :)
  • kayakaya Forumite
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    you cannnot accuratley judge fuel efficiency by volume guys and gals, sorry, petrol increases and decreases in volume according to its temperature, the only way to accurately judge fuel economy would be to weigh the fuel in the tank before and after the test period, trip computers in cars arent too good either, putting a different set of wheels/tyres on your car can make a huge difference to the reading also as your changing the outer circumference of the wheels
  • When I drive I aim to not have to use the brakes, I find this helps greatly, you are always consious of your speed because you have to think ahead, you tend not to drive too close to the car in front, you are constantly aware of the need to slow down at junctions etc and you save on wear to the braking system as well as becomming more confident and calm. I believe if more people adopted this form of driving there would be less problems on the roads The best way to drive is to be relaxed and calm and NOT to go racing around, every time you accelerate heavy you are pouring fuel into the engine, if you suddenly need to stop you strip material off your brakes....
    I drive a Ford Scorpio 2.3 and used to spend £50 a week on petrol. I had it converted to LPG and now spend about £25 a fortnight for the same mileage, I don't even bother to monitor the mileage now.
    When I first had it converted I went fro HULL to BRISTOL for £18.50... can't be bad...
  • When I started doing a long commute, I bought a Nissan Micra diesel for it's fuel economy. At first I used to commute up and down the A1, trying to make good speed, and I was getting almost 50mpg on the commute. But I soon realised that the congestion was such that it wasn't worth trying too hard, so I settled in to a more relaxed approach. Cars that were desparate to overtake me would still be in sight 30 miles later, so they'd saved themselves 30 seconds by hurrying! :confused: My consumption went up to nearly 60mpg. All these readings were taken via the onboard computer, so they're not absolutely accurate, but they were readily repeatable so give an excellent indication.

    I decided to try a similar approach on longer business journeys after a "slow" journey. Travelling at normal motorway speeds and keeping up with the traffic, I'd get around 50-55 mpg on a long journey. Then I had a trip where I seemed to follow a succession of wide loads, and my consumption went down (?up) to 78mpg! On the way back, I tried to repeat the approach, and stuck religiously to a 70mph maximum and accelerated more steadily. I got better at this (while still making decent journey times) and managed to get up to almost 80mpg. I often managed over 80mpg average for most of the journey, but it always seemd to drop to 79,9mpg by the end :mad: My average speed was only 1 or 2 mph less than previously (3%-ish), but my consumption improved by 40%, so I didn't have to stop so often for fuel, which actually improved my journey times.:T

    I remember an article in CAR magazine where they took a Porsche 911 Turbo across Australia on a derestricted road to see how fast they could manage. Despite travelling at 3-figure speeds, they found that they had to refuel so often that a regular car travelling at 70-odd was keeping pace with them. Hare & Tortoise :confused:
    Jumbo

    "You may have speed, but I have momentum"
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