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Thread: Cold Petrol!

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    Regular Member KC's Avatar
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    Default Cold Petrol!

    I hear time and time again that you should buy your petrol as early in the morning as you can as it will be more condensed due to the colder temperature.

    I don't know about you guys, but I think its a load of nonsense. I would have thought that as the tank is so far under ground that the day time temperatures would make very little difference. Might be a nano temp difference in the Winter, but still I think not enough to measure the diferences. What do you thinks guys codswallop!!

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    Full Member kenp's Avatar
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    Not colder in the morning... or atleast a very small difference..

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    Regular Member dv8's Avatar
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    I thought as the fuel was stored in underground tanks, its more or less the same temp!, i never have really believed in this..perhaps we can have a final answer from someone here....

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    Regular Member SignumPhil's Avatar
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    Quote Originally Posted by dv8 View Post
    I thought as the fuel was stored in underground tanks, its more or less the same temp!, i never have really believed in this..perhaps we can have a final answer from someone here....
    Just like you say, one of the reasons for storing it underground is to stop it getting too warm, so it'll always be around the same temperature, unless we have a really long run of hot weather. If it gets too warm the more volatile elements evaporate and the Octane rating reduces.

    Phil

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    Regular Member Ste's Avatar
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    Undergorund tank will have a fairly constant temp.

    However, when the tanker delivers fuel to it, the temp of the fuel in the tanker may be higher than the bulk in the underground storage, so it would be best to buy fuel after the temp has returned to normal in the bulk storage tank.

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    Regular Member VXR_DV's Avatar
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    I would have said that temperature isn't going to make any significant difference, unless you were planning to use the entire tank in the next half an hour or so

    Much more significant will be how "fresh" the fuel is. Fill up from anywhere that has a reasonable turnover (i.e. tanker turns up once a week or so), no problems. Fill up from somewhere very obscure where only lost tourists go, and the petrol has been down there for weeks/months, and the higher fractions will have evaporated off into the ozone layer...

    dv.

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    Regular Member Leviathan's Avatar
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    I have heard in the past that like most things, petrol when cold will contract and so if you buy in the morning when the ground is colder then the petrol will be too. As the ground warms up, so does the petrol which again expands and so you get less for your money.

    I have to say though, even if that is true (which I suppose it could be) the amount extra you get wouldnt be worth getting out of bed early for.

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    Regular Member SignumPhil's Avatar
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    Quote Originally Posted by VXR_DV View Post
    I would have said that temperature isn't going to make any significant difference, unless you were planning to use the entire tank in the next half an hour or so

    Much more significant will be how "fresh" the fuel is. Fill up from anywhere that has a reasonable turnover (i.e. tanker turns up once a week or so), no problems. Fill up from somewhere very obscure where only lost tourists go, and the petrol has been down there for weeks/months, and the higher fractions will have evaporated off into the ozone layer...

    dv.
    True. I've bought petrol from a French motorway service station before (not many French cars run on petrol, and they're too sharp to pay motorway prices if they do, so it sits around for a while!), and it really affected my trusty Mk1 Ocatvia L&K 1.8t. My fuel consumption shot up and it wasn't pulling very well. I though it was my car until my brother mentioned that his Vectra was having the same issues and he filled up the same time as me.

    Fractions, that's the word I was trying to remember!

    Phil

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    Regular Member JonV6's Avatar
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    It's true that fuel expands and contracts. I'm in the RAF and during summer months (not that we get many) we have to 'skim' fuel tanks....

    This means instead of filling them up to the stop, a gap is left in the top of the tanks to allow for expansion otherwise the fuel vents overboard in the afternoon heat!....

    Jet fuel being very similar to Diesel has pretty much the same thermal properties, but as others have mentioned, the fact that the fuel is stored underground probably means it doesn't vary in temperature so much, I'm guessing it's negligable!....

    I for one though would be prepared to get up earlier if it meant getting a few more miles out of a tank!

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    Regular Member G.O'Rilla's Avatar
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    re - the above post, I thought that all tanks from ship tanks to shore storage tanks had to have an ullage space above the liquid (or a safe limit if a floating roof tank). This allows for any expansion and is also the reason why car manufacturers say you should not top your tank up.

    Back to the original post, theoretically yes, in practice no. As a previous poster said, the fuel would warm up in the tank.
    However, with seasonal temperature variations, denser fuel in the winter should have more "bang for the buck". Didn't they ban low temperature fuels in formula one for this reason? - I think someone got disqualified last year for having fuel at too low a temperature.

    If I have time today (or can be bothered) I'll work out some volume changes using typical diesel densities and the ASTM volume correction tables - from memory it is probably about 1%
    Last edited by G.O'Rilla; 1st August 2008 at 06:56. Reason: can't write properly this time in the morning

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