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Petrol tank - to be or not to be full

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Petrol tank - to be or not to be full

Normally I put very little petrol each time I visit the garage (£10 or £15 worth) due to the high cost and I don't use the car that often.
We don't have a close garage and many times over the last few years I had been worried about running out. Last week, as I got a petrol allowance to get to my residential course I filled up. Since then I haven't let the gauge go much below 1/2. Less stress worrying about running out Wink
But, apart from that, is there any benefit/loss due to running with a tank between 1/2 and full as opposed to between 1/4 and fumes?

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Re: Petrol tank - to be or not to be full

Theoretically, at least, the extra weight of the fuel keeping the tank 1/2 to full will make your MPG worse.
If you go out of your way to fill up it may save money by filling up less often.
I normally run close to empty (but avoid running out) then fill right up but I do drive a good few mles, for less regular use I'd suggest keeping between 1/4 and 3/4.
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Re: Petrol tank - to be or not to be full

I'd heard that running less than a 1/4 full wasn't great due to the gunk that gathers at the bottom of the tank would find its way into the engine.
No idea if it's true.  I fill it all the way up weekly, though I do in excess of 300 miles a week.
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itsme
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Re: Petrol tank - to be or not to be full

I have always run mine from full to nearly vapours so would say my tank is gunk free, on average I fill up once a week.
shalom2010
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Re: Petrol tank - to be or not to be full

The great feature of my Ford Focus (& probably some other cars) it estimates how many miles you have left in your tank. The estimate seems to be very accurate, as it goes up when I'm doing a
full efficient speed (like 56 mph) and down quicker in town. The lowest it's been is 20 miles left in the tank when I got the car from new, where the gauge showed empty! I prefer to keep less than half
a tank as I don't do that many miles a month and as mentioned above you get more miles due to less weight.
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Re: Petrol tank - to be or not to be full

I'm completely the opposite to you guy's. I hardly ever let my tank drop below 1/2 to 2/3 full. A throw back from the tanker drivers disputes and shortages of a few years ago probably.
But how do you go about calculating the lost mileage from driving around with a full tank rather than an almost empty one? And over how many years do you base this saving? Most would probably save more fuel by learning not to accelerate so hard and anticipating breaking distances so they are more gentle. Ok so your car will do 0 to 60 in 6 seconds but if you're going to prove it every time you set off you'll pass anything on the road except a garage.
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Re: Petrol tank - to be or not to be full

I normally fill up once a week and that generally gets used fully so I end up with a near empty tank.
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Re: Petrol tank - to be or not to be full

Quote from: Petlew
But how do you go about calculating the lost mileage from driving around with a full tank ...

I was wondering that. My thoughts is that I'd doubt it'd add up to much in the short-term. Maybe over a year or the life of the car you'd notice a saving Undecided
Recently I decided to change my driving habits. Instead using motorways and driving at or above the speed limit to get from A to B as fast as possible I've started to use A and even some B roads with my speed averaging between 50 & 60.
First up, I found the journey to be more pleasurable and less stressful as well as the extra time taken to get there not being that much more and I just started out earlier anyway.
Secondly, I saw my fuel consumption go up (or is that down) from the mid-twenty mpg to just under 40 mpg. A bigger saving, I would have thought, than driving with a tank 1/4 to 1/2 full!

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shalom2010
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Re: Petrol tank - to be or not to be full

@Mav - I've been also doing the same. Totally agree - I also take my foot off the gas when going down hills (not sure if that helps though!)
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Re: Petrol tank - to be or not to be full

@Mav, entirely agree. I only use motorways when I have no choice and much prefer driving on A and B roads <they're much more "interesting">
And quite agree about the mpg saving by so doing.
@shalom2010, that doesn't work too well with automatics sadly. Before shutter comes in and tells us otherwise, dropping out of gear down hill (in a manual) and letting it coast (thought to be illegal) this has been discussed on this forum many times before.
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Re: Petrol tank - to be or not to be full

I avoid motorways whenever I can.  I find a much better driving experience on the A and B roads. Whenever I have to use a motorway it is generally the M25 which is a nightmare at all times.
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Re: Petrol tank - to be or not to be full

Quote from: dvorak
I'd heard that running less than a 1/4 full wasn't great due to the gunk that gathers at the bottom of the tank would find its way into the engine.
No idea if it's true.  I fill it all the way up weekly, though I do in excess of 300 miles a week.
That used to be true but on modern cars with fuel injection it is constantly circulated from the tank to the filter and back so there is no sludge at the bottom
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Re: Petrol tank - to be or not to be full

Quote from: shalom2010

I also take my foot off the gas when going down hills (not sure if that helps though!)

The only way you can calculate how much M.P.G. you get is to fill the tank to the brim..... drive (say) 300 miles..... re-fill to the brim and then work out the mpg ....
By doing that you will get a good idea of how efficient your driving is ( or  not )...  and also after a while, your average may increase... if there is anything wrong with the engine/fuel lines leaking/ injector not working properly, this can also be reflected in the figures.. so it is like taking your blood pressure on a regular basis..
My Skoda Fabia 1.9 SDI 2001 diesel, is rated in the Parkers guide book as doing 56mpg.... however with "freewheeling" as shalom says down hills, and the last 400 yards to a roundabout on high speed roads  ( you will stil need to brake from about 25 mph)  I have managed to get my "average" MPG up to a staggering 68.5 M.P.G.   I am now working towards an "average" of 70....
Bear in mind this engine has done over 199,000 miles .... and still Goes Like Stink, when I want it to ! ! ...   (Remember the GLS on the back of Ford cars  ? ?  )
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Re: Petrol tank - to be or not to be full

I use an app on my HTC called FuelLog - Car management.
At it's simplest you enter your fill-ups (or even part fill-ups), cost per litre, total litres and mileage (either trip or total) and it calculates everything for you along with averages.
You can also add other costs like insurance, maintenance, MOT, etc and it will giving a running cost per mile, per gallon and so on.
Quite a neat little app - and it's free Smiley

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Re: Petrol tank - to be or not to be full

The other point about only putting £10 in the tank, is that it "may" reduce your perceived need for a car journey,... i.e.  "I`ve only got a bit of petrol in the tank, so I`d better go straight home, instead of to another place first... "... or  " I`ll have to go to the garage and put some petrol in before I go to ...... "  thus you might put off journey`s to be done another day, ... however, you will still (probably) make those journeys..... (albeit on another day )....so there will be no saving ! ! ! ... 
Psychologically, filling up (with £10 ) every other day or so,  becomes a chore..... and having a full tank at the start of the week, is only one journey to the petrol station, instead of 4 or 5 .. and you are doing unnecessary jouneys using fuel to and from the petrol station... ( even if it is "on the way" occasionally) ...  The amount of money you spend on fuel per week, will be roughly the same.... given that fuel prices sometimes change from day to day.. you may fill up to the brim when it is cheaper, and then the next week you have to pay a bit more to fill up... and the alternative, £10 "top up" will give reduced quantity of fuel, when the price is higher, therefore your mileage figures will be different to a full tank .... !  ..