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• FIRST POST
fuzyfelt
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
Page 1
• robnye
• By robnye 7th Feb 05, 9:43 AM
• 5,332 Posts
• 1,121 Thanks
robnye
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
by fuzyfelt

what happens if the price of petrol goes up between your half tank fillings? .......
smile --- it makes people wonder what you are up to....
• DavidVince
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.
* 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.
• economiser
• 7th Feb 05, 6:06 PM
• 894 Posts
• 308 Thanks
economiser
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.
• vansboy
• By vansboy 7th Feb 05, 9:09 PM
• 6,138 Posts
• 4,425 Thanks
vansboy
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...

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
• fuzyfelt
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.
• Savvy_Sue
• 8th Feb 05, 1:21 AM
• 38,210 Posts
• 34,753 Thanks
Savvy_Sue
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!!
by vansboy
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.
Still knitting!
Completed: 1 adult cardigan, 3 baby jumpers, 3 shawls, 1 sweat band, 3 pairs baby bootees,
1 Wise Man Knitivity figure + 1 sheep, 2 pairs socks, 2 hats and 2 balaclavas for seamen ...
Current projects: another balaclava for myself, must find a mohair cardigan pattern ...
• carl310166
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.
• Trow
• By Trow 9th Feb 05, 6:54 PM
• 2,259 Posts
• 2,588 Thanks
Trow
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.
• Altarf
• By Altarf 9th Feb 05, 6:55 PM
• 2,851 Posts
• 1,679 Thanks
Altarf
* become friends with a farmer and buy some nice cheap red diesel.
by DavidVince
Cheap until you run into the nice men from C&E.........
• Silent_Bob
by vansboy
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
• ReductionQueen
• 12th Feb 05, 9:43 PM
• 208 Posts
• 5 Thanks
ReductionQueen
a few problems- -

* 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.

hope its of help.
by DavidVince
I think that you will find it's diesel, not petrol that's most commonly made from veg oil. After all, petrol is a spirit and would have to be distilled. I have looked into making biodeisel, and think it's a bit fiddly for my liking, but some older diesels can run on SVO, straight veg oil, but sometimes this needs heating slightly in the tank to make it thinner.

Also, I agree about other poster's comments about red diesel, best stay away from it. Though I must say that cars are almost never stopped at roadside checkpoints to be dipped for red diesel, usually commercial vehicles.
"Excuse me, this expires today, will you be reducing it?"
• vansboy
• By vansboy 13th Feb 05, 7:49 PM
• 6,138 Posts
• 4,425 Thanks
vansboy
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.

Driving a fuel hungry sports car that requires the highest RON rated fuel I can get (Optimax)
by Silent_Bob

Bob - ask the tanker driver HOW he selects the fuel from the depot!!

He'll tell you that they use a card, which allows CORRECT fuel/additive package, be dispensed, at the fuel depot.

It IS different!! & saves the need for any additional chemical agents to be used, when you get the car serviced.

Glad you're using Optimax - & hope you've got the Shell card & collecting the points, too!

VB
• empfun
Hi FuzzyFelt, as the members have covered most of the useful tips. I would like to re-iterate them and perhaps add one more.

1) Make sure your tyres are properly inflated.
2) Let your engine warm up fully if you have time before you drive it.
3) Don't drag the gears.
4) Change your engine and transmission oil regularly.
5) Replacing the spare tyre with a lightweight space saver spare will save you money in the long run. I took it one step further and did away with it completely. I never kept even the lightweight space saver spare at all, because I felt that the money I would save from having the dead weight would more than cover the call out for the AA (free for some).
Last edited by empfun; 13-02-2005 at 8:06 PM.
I know nothing
• Skint_Catt
• 15th Feb 05, 12:39 PM
• 11,431 Posts
• 23,689 Thanks
Skint_Catt
I'm desperate not to use any petrol but with a 42 mile round trip to work everyday(with no public transport as in the middle of nowhere) it's a bit hard.

I movd house once and did a 50 mile journey with a fish tank of goldfish on the passenger seat - trying not to spill/kill/make sick the goldfish I used so little petrol I try to remember how I drove. Not too bad when the roads are quiet but when you have zooming traffic around you I guess you have to keep with the flow!

Good Luck
• Jolaaled
• By Jolaaled 18th Feb 05, 8:37 AM
• 1,038 Posts
• 2,504 Thanks
Jolaaled
close all windows while you're moving. open windows create more drag.
Switch off any electrics not needed e.g. heated rear window, lights etc.
Rather than cruising in neutral, up to a junction, remain in a low gear ( not applicable to older cars tho').
• plasma258
i seem to get a different amount of miles per tank depending on where i fill up.

I seem to get atleast 10-15% less mileage if i use supermarket petrol, i find the best mileage is from Total where i get about 330 miles per tank instead of about 300 from BP, where as supermarket petrol gives me about 270!!

Does anybody else find this?
• ReductionQueen
• 18th Feb 05, 11:55 AM
• 208 Posts
• 5 Thanks
ReductionQueen
Don't forget, if you use ariconditioning (OK, not really relevant in february but....), your milage will drop through the floor. I.e. you will use much more petrol when it's on, as your engine has to work harder to power the car as well as the aircon.
"Excuse me, this expires today, will you be reducing it?"
• YorkshireBoy
• 19th Feb 05, 2:30 AM
• 30,025 Posts
• 17,888 Thanks
YorkshireBoy
5) Replacing the spare tyre with a lightweight space saver spare will save you money in the long run. I took it one step further and did away with it completely. I never kept even the lightweight space saver spare at all, because I felt that the money I would save from having the dead weight would more than cover the call out for the AA (free for some).
by empfun
Isn't this illegal?
• toozie
• By toozie 19th Feb 05, 7:42 AM
• 3,246 Posts
• 5,904 Thanks
toozie
plasma258 i seem to get a different amount of miles per tank depending on where i fill up.

I seem to get atleast 10-15% less mileage if i use supermarket petrol, i find the best mileage is from Total where i get about 330 miles per tank instead of about 300 from BP, where as supermarket petrol gives me about 270!!

Does anybody else find this?

I would use Total, but I live in a very rural area, the Total price here is far more expensive than at another TOTAL 45 miles away.

Just because of this I go to Tesco, 20 miles away-near my office.