# A way to use less petrol?

Posts: 54 Forumite
Hi all,
I've been wondering for a while if this works, and just doing some quick calcs in my head maybe somebody could tell me if my working's wrong...

If I only fill up my car 1/2 full of petrol each time, do I save 'cos the car's more efficient 'cos it's not carrying around the extra 1/2 tank of petrol?

Based on these figures:
1000 kg car,
40 litre tank capacity which is about 40 kg,
full tank every week, about £30.

I calculate ruffly:
20kg ( half a tank ) is 2% of the weight of the car, so uses 2% less petrol.
2% of £30 is 60p x 52 = £31.20 per year.

I'm sure there's some complex integrals and stuff that can be used, but is there anything wrong with the basic idea? Is this an easy way to save £31.20 per year? Anyone got more info so we can work it out accurately? Does BP not want us to know this?

Andy

• Posts: 5,411
Forumite
fuzyfelt wrote:
Hi all,
I've been wondering for a while if this works, and just doing some quick calcs in my head maybe somebody could tell me if my working's wrong...

If I only fill up my car 1/2 full of petrol each time, do I save 'cos the car's more efficient 'cos it's not carrying around the extra 1/2 tank of petrol?

Based on these figures:
1000 kg car,
40 litre tank capacity which is about 40 kg,
full tank every week, about £30.

I calculate ruffly:
20kg ( half a tank ) is 2% of the weight of the car, so uses 2% less petrol.
2% of £30 is 60p x 52 = £31.20 per year.

I'm sure there's some complex integrals and stuff that can be used, but is there anything wrong with the basic idea? Is this an easy way to save £31.20 per year? Anyone got more info so we can work it out accurately? Does BP not want us to know this?

Andy

what happens if the price of petrol goes up between your half tank fillings? ....... :eek:
smile --- it makes people wonder what you are up to.... :cool:
• Posts: 44 Forumite
a few problems- -

firstly the petrol you save - some will be spent going to re-fuel on a mroe regualr basis.
secondly, other features of your car add far more weight - example spare tyre - replacing this for a space saver light tyre has the advangtage of weight - however they do need to be replaced within a 40km distance.

the best petrol saving tips i find are...

* keep your engine tuned correctly (you can do this yourself cheaply from maplin if your willing to have a go)
* hit 5th/6th gear by 37mph
* cruise if you do not have modern car or a modern car form a less developed manufacture (for example kia) - modren engine systems (for eample renault) cut of petrol usiage when the accelerator isnt applied and the car is in motion in gear.
however, it will use petrol if the car is ;left cruising out of gear to keep it turning over. other manufacturers such as kia are not up to date on such technology on a large proportion of their engines.
* consider an lpg convert
* consider a diesel
* but an old diesel (preferbly non turbo or early turbo, do a few internet searches and finfd out how to make your used cooking oil into petrol - its alpot easier than you think. by law you should report and pay all duty on the fuel you use. i know of firneds who have used and continue to use this very successfully.
the only main odwnside - is a very slight loss in power (its a non turbo diesel - as if you care anyway, not reccomend when its going to be very cold (although adding a drop of petrol and diesl seems to do the trick). even paying the duty - you can still work out as 25p a litre, and msell like a chip shop - ther are ways to reduce the smell.
i could go on alot more about this - way to much detail to go into.
* become friends with a farmer and buy some nice cheap red diesel.
* dont do a car journey for less than 10 mins or 5 miles. you will wreck the engine over time and destroy your fuel economy.
* motorway speeds of 55-60 are ideal for maximising mpg.
* stick to petrol engines no bigger than 1.3/1.4

hope its of help.
• Posts: 897 Forumite
Fuel consumption is not proportional to weight. It is a significant factor, particularly when accelerating, but has little effect when running on the flat at constant speed.
• Posts: 6,483
Forumite
Some of DavidVinces ideas are fine, but...

Beware the tip to get into higher gear too soon. This is for 2 reasons,

1 - you can cause the engine to 'labour' making it less efficient & strugle to catch up with the speed your doing.It won't be a smooth ride, either.

2 - current feeling among many professional drivers & those skilled in advanced driving techniques, favour lower gears, in town & built up areas, for better control & safer driving.

If you maintain 3rd gear at the 30mph limit, you may use a little more fuel, but your control of the car will be greater & the flexibility from it will be VERY apparent. Similarly 4th gear at under 40mph limit.TRY IT!!

& for my suggestions...

Forget supermarket fuel (lots of debate about this, but it IS a different product.

Use Shell - get a Bonuspoints card, worth nearly 1p/ltr, depending on spend levels.

Get a Shell credit card - use it once & they give you £10 free petrol, by points/voucher.

Run the tank 'till you've got a gallon or so left, then brim it as full as you can, 'till the first click of the nozzle. Don't go past this, 'cos in the summer, you'll find the fuel expands & you'll loose it via overflow.

In summer, re-fuel in the early morning, as for reason above, the petrol station's supply will NOT have expanded during the heat of the day.

Plenty more ideas in http://www.honestjohn.co.uk for ALL things motoring

VB
• Posts: 54 Forumite
Thanks for the replies. Just an idea that's been in my head for a while, probably is a bit silly...

Some good advice for fuel economy, if sometimes a bit conflicting...

Ta.
• Posts: 45,806
Forumite
vansboy wrote:
If you maintain 3rd gear at the 30mph limit, you may use a little more fuel, but your control of the car will be greater & the flexibility from it will be VERY apparent. Similarly 4th gear at under 40mph limit.TRY IT!!
VB's advice here will also help you avoid collecting speeding fines. It is quite hard to exceed 30 in 3rd gear without realising it, and very easy to exceed 30 in 4th. The Institute of Advanced Motorists says “WRONG GEAR” CONTRIBUTING TO SAFETY CAMERA MISERY - and that the way we were taught to drive "in my day", ie changing up as fast as possible - isn't the way to do it.
Signature removed for peace of mind
• Posts: 747 Forumite
Tip's to save fuel are.

Remove anything that increases wind resistance,eg roof rack.

Any excess weight,eg toolbox in boot

Drive like you have an egg under the throttle.

Tyre pressures are vey important.

See here..

for fuel ecomony tips,although the guys on this forum tend to vent (fill to brim,by letting all the air out)their deisels,but beware of the expansion of fuel as posted previously.

Weight is important,but by venting you can get a very accurate measure of mpg's,i think that's why they do it.
Sponsored by Tesco Clubcard Points !!
• Posts: 2,298
Forumite
Using the tip about red diesel could prove to very *very* costly should you get caught - fines over £1,000 are not uncommon.

Being caught may be unlikely - but there is always a possibility and I know of more than one driver lcoally caught over the last two years.
• Posts: 2,916
Forumite
DavidVince wrote:
* become friends with a farmer and buy some nice cheap red diesel.

Cheap until you run into the nice men from C&E.........
• Posts: 1,014 Forumite
vansboy wrote:
Forget supermarket fuel (lots of debate about this, but it IS a different product.

Sorry to disagree but you're wrong. All fuels have to conform to a rigorous standard procedure. i.e. Sainsburys unleaded and super is the same as BP's.
Stations have to test their fuel in their tanks on a weekly basis too for quality.

Additionally most of the time they fill up from the same fuel depots. There's one near me and I regularly see Esso, Shell, Texaco, Sainsburys tankers etc filling up there - and this is a BP depot.

The only difference is they may not contain cleaning agents, which if you have you car serviced regularly or use an engine cleaner every 3 months will do the same job.

As for the weight of fuel making a difference it does at 1kg a litre that extra half a tank makes a huge difference. On half a tank I get about 33-35 mpg, but this drops to 28-30 on a full tank when doing the same driving week in week out.

Having the correct tyres pressures is the other overiding factor too for good fuel consumption as is clearing the car out of any unneeded weight.

Driving a fuel hungry sports car that requires the highest RON rated fuel I can get (Optimax) which is overpriced requires use of the fuel saving measures outlined. As the garage where I fill up is on my daily route there is no additional mileage in going to fill up.

Hope this helps
Never argue with an idiot. He will bring you down to his level and beat you with experience.

Snoochie Boochies
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