Volume of Petrol Delivered During Cold Weather at the Pump

Niall1234

Often heard that you get a bit more petrol for your money when its cold due to the petrol being more dense.

Anyone care to guess how much more petrol your actually getting ?

Do the petrol companies up the price in light of this ?

Owen

I'd say there's a touch of the urban myth about that one!

peasant

No, there isn't ...well, not entirely

Fill up your car to the very brim with cold petrol from the underground tank and leave it out in searing heat ...you fill find that after a while petrol comes seeping back out of the tank.

Cold petrol (and diesel) is denser and expands when warm

But I would expect the metering of the pump to take that into account, so you get what you pay for, regardless of temperature/density

Owen

Everything expands when warm, nice and warm. But at 10 or so degrees (Average Irish temp) and below, I think Petrol will have the same density, and it's freezing point is below zero.

Del2005

It's true, liquids expand when hot and contract when cool, and since petrol and diesel are sold by volume it will have an effect. That's one reason why the seas are rising, no as much to do with ice melting as most of that is already floating in it. Don't know how much extra you get in winter, won't be too much, but I seen on a TV show a while ago about that and they said the you where better off filling your car late at night in summer as the tanks will be hot during the day and the petrol would expand therefore giving less fuel for the same volume.

Seth Brundle

Niall1234 wrote: »

Often heard that you get a bit more petrol for your money when its cold due to the petrol being more dense.

Anyone care to guess how much more petrol your actually getting ?

Do the petrol companies up the price in light of this ?

Going by work that I have done within the industry, its charged per litre at 15degrees Celsius.

Stephen

Del2005 wrote: »

Don't know how much extra you get in winter, won't be too much, but I seen on a TV show a while ago about that and they said the you where better off filling your car late at night in summer as the tanks will be hot during the day and the petrol would expand therefore giving less fuel for the same volume.

I can't imagine the tanks get very much hotter at all in the summer daytime as opposed to night time, given that in pretty much every petrol station they're underground anyway.

Anan1

Del2005 wrote: »

but I seen on a TV show a while ago about that and they said the you where better off filling your car late at night in summer as the tanks will be hot during the day and the petrol would expand therefore giving less fuel for the same volume.

By that reasoning, wouldn't morning be better?

patrickc

like the myth the slower you put the fuel into your car the more you'll get for less

kona

im sorry doesnt ice expand??, hence the colder a liquid is the more dense??, so if its warm its less dense???

Niall1234

kona wrote: »

im sorry doesnt ice expand??, hence the colder a liquid is the more dense??, so if its warm its less dense???

Water is very ionic. That is the molecule is full of minuses and pluses. When water freezes it forms a crystal who's structure is larger than liquid water just floating around.

When ice drops below -4C it begins to contract again.

Carbon Dioxide does something similar, except that CO2 has no liquid state. Goes straight from gas to dry ice and back.


Petrol has no water in it at all and is not an ionic molecule. It will always get more dense as it cools.

kona

Niall1234 wrote: »

Water is very ionic. That is the molecule is full of minuses and pluses. When water freezes it forms a crystal who's structure is larger than liquid water just floating around.

When ice drops below -4C it begins to contract again.

Carbon Dioxide does something similar, except that CO2 has no liquid state. Goes straight from gas to dry ice and back.


Petrol has no water in it at all and is not an ionic molecule. It will always get more dense as it cools.

somebody listened in chemistry:D;)

Del2005

Anan1 wrote: »

By that reasoning, wouldn't morning be better?

Yes, but the amount of extra fuel you get is tiny anyhow so makes no real difference

kona wrote: »

im sorry doesnt ice expand??, hence the colder a liquid is the more dense??, so if its warm its less dense???

I meant the water is expanding due to global warming. People think the sea levels are rising because the ice is melting, which if coming from land is true but again only a small amout, whereas the water is expanding due to heating creating a bigger rise.

Seth Brundle

Niall1234 wrote: »

Petrol has no water in it at all and is not an ionic molecule. It will always get more dense as it cools.

There is no water in petrol but a small percentage of the contents of each ship, depot storage tank, lorry and presumably forecourt tank is water. Now whether this manages to get pumped into the car's fuel is another matter - I don't know what methods are used to get it out of the forecourt tank.

Niall1234

Niall1234 wrote: »

Often heard that you get a bit more petrol for your money when its cold due to the petrol being more dense.

Anyone care to guess how much more petrol your actually getting ?

Do the petrol companies up the price in light of this ?

From what I understand you are proabably not going to notice the difference. However for the likes of large petrol stations it is significant and they probably add it in their balance sheet somewhere.

milltown

Actually, when the fuel is pumped off the ships into the tanks down the docks, rather than leave hundreds or thousands of gallons in the pipes between the dock and the fuel terminal they pump seawater through after the fuel to push it all to the tank. So at the depot at least there is quite a bit of water in the mix.

Nowt' to do with the OP, just sayin'.

Mailman

You might get a mile or two further thanks to it being more compressed but your real fuel economies in the winter will come from the natural intercooler effect of a lower ambient temperature when running your engine in cold weather.
Of course if you switch on your lights and demister then most of this saving is lost.

daveharnett

milltown wrote: »

Actually, when the fuel is pumped off the ships into the tanks down the docks, rather than leave hundreds or thousands of gallons in the pipes between the dock and the fuel terminal they pump seawater through after the fuel to push it all to the tank. So at the depot at least there is quite a bit of water in the mix.

Nowt' to do with the OP, just sayin'.

Wouldn't it settle to the bottom, where they could just pour it out (ie open a tap on the bottom of the tank until petrol starts coming out)?

The difference in density between petrol at 40C and 0C is 5% at best apparently. Trouble is the underground tanks would change temprature VERY slowly, and according to google, the pumps take temp into account anyway. Lousy.