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

Dave72_2

hope no one else has said this, but there are 12 pages to this topic.
....When slowing down, eg for a junction or roundabout, does everyone stay in top gear until the speed drops to such a point that you need to dip the clutch (at around 30mph). Doing so will save several gear changes (save on wear and tear), and also with your foot of the power, you will make use of the eco valve on modern cars - you will use almost no fuel at all in this situation (even less than using N).
Other points to note is when going up in speed, if the road goes down hill a bit, you dont need to always go through every gear, eg 1,2,3,4,5. You can *block change* eg 1,2,4,5. The hill adds enough extra speed to enable this to work. I was quite shocked a few weeks ago, while this subject came up on another site, that some people downchanging 5,4,3,2, and even using 1st to slow up, even though by that time they are almost stopped moving.

(manual or stick shift cars only).

I drive a TDI 1.4 Polo (the one thats just been replaced). Mostly its quite good on diesel miles. But I did find on the motorway it uses a lot more fuel at 70mph compared with 60mph. Also the needle drops back faster if there are other people in the car with me - extra weight. It turns out the 1.4TDI is a tad stressed in my shape Polo - VW have put a slightly bigger (1.6) TDI engine in the new shape Polo, and the new one weighs a bit less than my one as well. Hence, high speeds and extra weight hurt the fuel usage more than expected.

A short time ago, I did a test to see how far I could go on a single tank of fuel. I drive mostly on busy roads, with plenty of roundabouts and traffic lights, so quite a bit of stop-start driving. Also quite a few hills, so far from ideal conditions. I managed 536miles in these conditions from a single tank of diesel (£50). The fuel low warning lamp had been on quite a while (approx 20miles) when I pulled in to refill, and needle was on the stop. It does its best miles at about 55-60mph, so I think if all my miles were at that and in one hit, I could get 600miles out of it.

katyboo123

I must be the only person who can't get more mpg out of her car! I have a Fiesta and I keep the tyres pumped up correctly, the mechanics in good working order, fluid levels correct, half filled tank rather than fully filled and NEVER past the click, never let it go too low, I carry a light load, with only my breakdown survival kit in the boot (I travel alone 95% of the time). I drive carefully, I was lucky enough to drive a brand new car a while ago through work, and that taught me a lesson on driving efficiently (showed how many mpg you were getting at anyone time). Anyways, I do it all by the book and still, only get same mpg!

Nevermind, Asda reduced petrol by 1p a litre this week, so I will get a little more now! x

Dave72_2

Is that a petrol or diesel fiesta.....diesel fiestas in recent years are quite economical (or so they say).

Try changing up gear at about 2000rpm (diesel, a bit higher for petrol). Aim to be in 4th gear at or just above 30mph. 5th gear at or just above 40mph. This will feel very slow indeed.

small cars v large cars.....

I used to have a Corsa (last shape) 1.2 petrol. The fuel economy was quite poor on that. Infact it wasnt much better than the car I replaced it with - an Astra petrol 1.8 automatic. I think in some cases, depending on situation you can have too little power - so much so that the little engine is working overtime, just to carry (for example) 3 people.
This still holds true for me now. After the Astra, I now have a diesel Polo TDI (1.4). So it is much more economical, but by how much depends on the situation. Driver only, on A roads at 50-60mph, its loads more economical, and also in traffic (although nowhere near as nice to drive in traffic). But when there are 4 of us in the Polo, the economy drops away quite quickly. Same thing happens, when driver only but driving the car quickly (well, as quickly as a TDI 1.4 Polo can go), or at motorway speeds. But I remember in the Astra, nothing much happened to economy if there were 5 of us in it, or driving at motorway speeds. It did get worse, but the drop off wasnt that much. In the Polo TDI the drop off is significant. It would still be more economical but by nowhere near as much.

My theory is, small 1.4 TDI engine cant cope with anything more than driver only and normal speeds.

harryhound

Some time back the AA published experiments with two petrol cars, a largish Honda and a Fiesta. Treated gently at 55 MPH the Fiesta was significantly better than the Honda, but "thrashed" at 80 on a motorway the Fiesta was no better than the Honda.

geoffholman

I read that you should drive with reference to your rev counter. Keep it below 2500 and you will save on petrol. I am trying this and so far seem to have saved around 3mpg. During this experiment I also found that the computer on my Honda Jazz gives consumption as 2mpg better than actual...

Dave72_2

with certain cars you may not be able to boost economy as much as with others. For example the Honda Jazz, with the 1.4 dsi petrol engine some how retards its self in traffic to save fuel. Driving for economy therefore wont boost its economy as much as if the Jazz didnt do this.

nicklansley

Great article, Martin, and its "kind of" been working for me too now I have thought about it - when towing my caravan!

I've only just recently joined the world of caravanning (life stage thing, whatever ).

I soon noticed that, when towing it, a tank of fuel was going MUCH further (like 50 miles further, delivering 300 miles/tank in my 12 month-old 1.6 Volvo C30) than before, which I thought was crazy until I realised:

1. I tow at no more than 50mph.
2. I accelerate gently on the accelerator, not harshly.
3. I brake in good time, gently and slowly.
4. I get out onto the motorways and avoid urban city roads as much as possible.
5. I use the cruise control and detect the best gear by occasionally pushing down on the accelerator. If I find myself accelerating I go up a gear. If I find no acceleration at all when I push the pedal down (so the engine is labouring at full throttle) I go down a gear. Wow does this seem to make a difference by finding the engine's "sweet spot" at 50mph with the varying slopes up and down.
6. I am hyper-alert for anything 'bad' that might happen on the road and take my foot of the power and cover the brake at the slightest hint of a problem being caused by another road user.

Of course the car must use more fuel accelerating and cruising, but not much more. On the other hand, on gentle downward slopes found on motorways like the M1 I have my foot hardly touching the accelerator and let the caravan's momentum push me forward.

Now of course I find myself applying this technique whether towing or not and I find that not only is the car under less stress and less fuel-hungry but I have a changed attitude too.

Thank you, fuel-saving caravanning life-change!

Cheers
Nick

almillar

With ref to the caravan story above - I do sortof believe it, driver has changed so many other factors (esp route) to make up for the extra weight/drag.
If you haven't got a caravan handy, try installing a spike on the steering wheel. This will certainly make you hyper alert and drive more carefully!

Navvy

This may sound daft, but try putting your seat back a notch.

If you have to stretch your leg to push the accelerator, you will find it easier to drive gently. If your seat is too far forward you will find it more uncomfortable to hold your foot poised lightly over the pedal.

mushypeaman

Been trying all this for a week now, and been subjected to a fair amount of aggro from other drivers, including a couple of shouted threats, due to not accellerating away from traffic lights quickly enough; slowing down too early (for them) when approaching junctions/roundabouts. Unpleasant.