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

emjay99

I once had to make a journey of 25 miles behind another car that was in a hurry. I did not know the destination and had to be sure not to lose the leader. It started at 8.15 am on a working day. I had to drive hard to ensure that no vehicle got between us. My Fabia 2.0 recorded 26 mpg for the journey. I then returned by the same route driving normally and got a recorded mpg of 37.5 - 50% more mpg.

harryhound

funky1471 wrote: »

Also remember your cars speedo is likely to be over-reading by approximately 10%, maybe a bit lower, so when you think you are going 70 its closer to 63-65.

I thought I was doing 40 MPH in a 40MPH limit.
Mr GATSO said I was doing 37 MPH in a 30 MPH limit :mad::mad::mad:

charlieheard

beans wrote: »

Surely the reason for mileage computers '"max-out" at some reading like 99.9 mpg', is that the car is moving without using fuel. .... Surely, it stands to reason that miles / gallon or kilometers / litre, if the divisor is zero, the mathematical result of distance / fuel is very large - not very surprising!

You're quoting back exactly what I said so, no, it's not very surprising :rolleyes: .

FWIW you don't get km/l - instead you get l/100km. This means that you will get a zero reading when you're using no fuel. The problem is that very few people in this country know what a reading of 4l/100km means...

beans wrote: »

Driving in too low a gear is essential for optimum fuel efficiency.
Far too many people drive in too high a gear causing the engine to labour, which is inefficient. A labouring engine is audibly different from a normally running engine.

In the absence of a fuel mileage computer, a good start is to change up before 2,500rpm (petrol) and 2,000rpm (diesel).

Poppycock! Driving in too low a gear wrecks economy, as engines become much less efficient at higher rpm unless working flat out. My Micra diesel was gutless below 2250, so changing up at 2000 would make it even worse. Read my earlier post for an explanation...

charlieheard

bookwormem wrote: »

Hi everyone! :j Never posted on here before.

A friend told me that she was taught that a good way of saving fuel is to only use 1st, 3rd, & 5th gear. I'd never heard of this before, and I think it sounds like a lot of nonsense, I don't know how it would help. However, my friend says it works wonders and the people who taught her this method had tried it out a lot. Any thoughts? Anyone tried this?

Hi, and welcome to the forums.:beer:

The reason that this might work is that it would force a petrol engine to work harder at lower rpm as you'd make it operate at lower rprm when you skip a gear. This might be more efficient - see here for an earlier post on the subject. Far better to avoid excessive acceleration and braking, and just travel slightly more slowly. It only takes a few minutes longer (say 5%), but saves lots of fuel (say 25%)

As an aside, I'm always amazed at those cars that speed off into the distance, only to get to the next hold-up/light/queue/junction more quickly and wait there for me to catch up a very short while later. Time saved nill - fuel wasted loads...

charlieheard

scape wrote: »

I tried this experiment in a 1.25 Fiesta on a 196 mile journey to North Wales from London. On the way there I drove very carefully, and aimed for a constant motorway cruising speed of 69 miles per hour (I heard somewhere this was an optimum speed.) On the way back, I drove hard and fast (within speed limits, and still being safe).

It didn't seem to make any difference to fuel consumption at all! I started both legs with a jam packed full tank and at the end of each leg, the fuelometer read 2 thirds of a tank had been used.

Has anyone had similar results?

Is it because I have an induction kit fitted (fancy air filter, apparently it boost performance, but a lot of people say it just makes noise)?

Interesting.

I've had a very different experience, improving my economy from 55 to 80 mpg. Saying there's one third of a tank left is fairly imprecise - it could be a gallon either way (i.e over £5). Equally, filling a car to the brim can be inaccurate as even a slight slope could mean an extra half gallon in the tank (another £2.50). As long as it's a modern-ish fuel-injected car, the induction kit will have little effect on the engine management system as long as it's fitted properly and in the correct place.

When car magazines really want to measure it accurately, they fill up just before they leave, making sure to bounce the car when it's full as air pockets can allow another half gallon in. As soon as they reach their destination, they do the same - the second amount is the actual quantity of fuel used. For more accuracy, they keep a log of fuel used and distance traveled over time, as this will reduce the inaccuracy in fuel measurements considerably. But then they need to be sure the mileometer is right by checking it against the 100m posts on the motorway... But that's going a bit far.:D

charlieheard

kwmlondon wrote: »

At 90mph a Rolls Royce will be more efficient than something like a Smart car as it is barely ticking over.

Despite the derision, you may have a point - is it better to use a larger engine lightly or a smaller engine hard? I've now got a 2.0l version of an people carrier, whereas before we had a 1.7l. The overall economy for both is almost identical, with the smaller engine being more economical around town and the larger engine more economical on longer journeys

In this case, the Rolls will be showing over 85% on its power reserve meter (rev counters are so non-U ), whereas the Smart will be flat out, using all the fuel it can.

Skeksis

Another tip to save fuel is to remove the spare wheel to lighten the weight of the car and keep a can of tyre sealant in the car in case of an emergency.

artistoz

An interesting experiment - but I think we need to remember to keep sight of other issues especially those concerning safety.... such as driving predictably! If the aforementioned methods are taken too literally, we'd have cars floundering around with drivers running up the back of them as they tip toe around trying to save fuel, or not pulling out of junctions fast enough so theyre sitting ducks for approaching traffic.
As for the other poster who recommended sitting behind trucks to save fuel - crazy. The best way of saving fuel in my opinion is to keep a good gap to the car infront so you dont have to brake at all! Funnily enough, thats safer too, and eases congestion.
Another factor also to be considered as sort of mentioned earlier includes servicing - especially filters.

Also consider cars are more fuel efficient in their designed rev range - too low rpm is NOT more efficient - and also damages your clutch, and the now common dual mass flywheel. Taxi drivers are renowned for this - 30mph in 5th triyng to save fuel, puts too much torque through the clutch and flywheel..... with around a 1k repair bill!

Ive also found BP Ultimate to be slightly more efficent £ per mile. It takes a couple of tanks to see the difference though as the cars ecu figures out the new fuel dose required so dont expect to be able to compare immediately.

A 6spd box will be more efficient on motorways due to higher cruise gearing, therefore lower rpm.

savethehoneybees

I drive 30k-40k miles pa and some cars have needed servicing every 10-12k miles. However, I've always been able to obtain an extra 3k-4k miles on the brake pads simply by avoiding racing up to a juction and then having to brake hard (it's amazing how many morons do this, causing others whom they've just cut up to also brake hard).
A saving of 25%-33% is worth having.

I've also just bought a Skoda Fabia 1.9 Diesel Estate which achives virtually 59 mpg; Fab!

Tojo_Ralph

Skeksis wrote: »

Another tip to save fuel is to remove the spare wheel to lighten the weight of the car and keep a can of tyre sealant in the car in case of an emergency.

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:rotfl: