Petrol - Urban Myths

Westmeath Lass

I was just wondering if someone would be able to help me with regard to Petrol. I was just having a conversation with a couple of work colleagues and the subject came up about prices of Petrol ETC. A couple of people said that certain companies don’t sell as good quality petrol as others i.e. not getting as much mileage out of it. Others said that a good time to fill petrol is early in the morning and to fill it slowly?


Has anyone ever heard anything like this or is it an urban legend type thing?


Thanks

Jen

mikemac

Urban myth

Though Topaz are marketing their "clean" fuel

mike65

Cold fuel is denser so more will fit in the tank (but it wont be any cheaper!).

Mike

randomer

With Maxol E5 petrol I get better mileage in my turbo car, but worse mileage in the N/A car.

It is the opposite with Esso.

Westmeath Lass

micmclo wrote: »

Urban myth

Though Topaz are marketing their "clean" fuel

Well it was just news to me that the majority of the people at the table all swore that they would not buy their petrol from two of the bigger companies as there was no running in it, "Your petrol disappears if you buy it from...." Kinda thing

Malice

Westmeath Lass wrote: »

Others said that a good time to fill petrol is early in the morning and to fill it slowly?

I'm not sure about the filling slowly part (I'm usually too impatient to do that ) but I've definitely heard that filling up early in the morning is better because the fuel has settled in the reservoir overnight and as Mike65 says, it's denser then too due to the air temperature.

faceman

Its not really a myth as such, its do with the how clean the petrol is. Thats why i use Cilit bang to wash my petrol tank every week.

Westmeath Lass

faceman wrote: »

Its not really a myth as such, its do with the how clean the petrol is. Thats why i use Cilit bang to wash my petrol tank every week.

Cilit Bang ?? Are you serious ? :eek:

mickdw

mike65 wrote: »

Cold fuel is denser so more will fit in the tank (but it wont be any cheaper!).

Mike

If its denser and you pay by the litre(Volume) not weight, then you will get more for your money.
Another tip I heard is not to fill up when the tanker is filling the service station tanks as all the grit will be stired up.
I heard the filling slow one too and although I always laughed at this idea, when I red about it lately, it made perfect sense but I cannot remember now why.

Overall though, I think you could save more by never driving around with full tank and also making sure you dont leave a load of petrol in the pipe when filling your petrol

seamus

Westmeath Lass wrote: »

A couple of people said that certain companies don’t sell as good quality petrol as others i.e. not getting as much mileage out of it.

Couldn't tell you about this, but I imagine that petrol has to pass certain tests before they can label it as being 95 or 98 or whatever. I would very much doubt that you would notice the difference between two different brands of 95 octane.

Others said that a good time to fill petrol is early in the morning and to fill it slowly?

The idea behind it is sound, though I don't know what effect filling it slowly would have. The idea is that when petrol heats up it expands, thus a litre of petrol at 5 degrees celcius, is "less" then 1 litre of petrol at zero degrees.
Again, I doubt it makes a big difference. Most stations store their petrol in huge tanks underneath the ground, so the temperature is not really affected by the ambient temperature (or the wind or sun) above the ground. It's likely that there is some temperature variance between summer and winter (like the oceans), but I'd be very skeptical about the temperature changing in a matter of hours on a normal day.

As others have said, the air temperature may have some effect, but very little IMO.

malice_

malice_ wrote: »

I'm not sure about the filling slowly part (I'm usually too impatient to do that ) but I've definitely heard that filling up early in the morning is better because the fuel has settled in the reservoir overnight and as Mike65 says, it's denser then too due to the air temperature.

I'm not so sure its of any benefit these days. I might be wrong.

Although I know for a fact very large petrol stations used to account for product effectively lost due to temperature variations, ie different amounts pumped due to density.

I know a company that used to sell products to do this. It was only the really large stations that were worried about thing things like this as its such a small amount relative to what is sold. But it would add up if you had many pumps.

Wertz

micmclo wrote: »

Urban myth

Though Topaz are marketing their "clean" fuel

Yeah wtf is up with that? Statoil recently got annexed here and on their price boards, they claim to be selling clean diesel and unleaded...is that to imply that everyone else's is dirty?

Quint

As for grit in the petrol, that's what your fuel filter is for

L1011

I would presume - but could find no info on the flyer or website - that Topaz "Clean Unleaded" is E5, just like Maxol and many others sell.

All fuel meets basic quality standards, most of it comes from common sources. Individual retailers may use different additives to other ones; and theres the difference of E5 vs. 'normal' 95RON...

In general, I've found I get the worst mileage by a noticeable amount off Tescos, but their station is filthy and poorly maintained so this may cause it more than anything else for all I know.

Vain

I always used to get petrol from esso i started using topaz 3weeks ago and im getting alot more mileage every week now from the same journey everyday. So i do think topaz has better petrol cant see how else id be getting better mileage from the same driving.

Unregistered.

Westmeath Lass wrote: »

A couple of people said that certain companies don’t sell as good quality petrol as others i.e. not getting as much mileage out of it
Others said that a good time to fill petrol is early in the morning and to fill it slowly?

Hey jen!
I like the idea of the urban myths, heard them myself, but i can "demythify" them if you like!...

Some companies petrol differ in that some offer petrol with a higher octane rating. This means that engine knocking is reduced, making it more effiecient! but if they're all selling the same bog standard 95octane(or 98?) then it should be all the same.... the problem of getting more mileage from one company's petrol that another's could be part of a more sinister conspiracy..(fiddling with the pumps so you get less, or that it pumps out the very minimum tolerance in the inspection standard!)

Regarding filling up in the morning... Well, the idea was clever.. petrol would be denser in the cold than in when it's warm. So you would get more(mass-wise) in a litre! However!! The petrol is stored underground, where the temperature change would be a lot less than it is on the outside. So even though the air is cold, the temperature of the petrol may have only changed by 1 or two degrees.
I have also heard that modern-day pumps will self-adjust based on the petrol temp, to ensure the same amount of petrol each time!

I have a good tip so you get more mileage! Don't let your tank get too much below halfway before filling! When you have a low amount of fuel in the tank, it will be easier to vaporise in the tank (due to it being easier to heat up from the air temp coz there is less) and the more empty space you have in the tank, the more the petrol will vaporise to fill the space. Now the fuel gauge doesn't read the amount of petrol vapour their is, and it will tell you that you need to fill up!
So when you keep more petrol in the tank, it requires more energy to become a vapour which it cannot get from the air temp!


EDIT: Filling the tank slowly!! I think you benfit from this for two reasons: because it does not stir up the petrol from the resevoir as much as fast-filling. Thus meaning the grit wont be disturbed to much and wont go into your tank.
the second way, is down to the pump's clever little design. It is designed so that petrol flows out of it into your tank, AND to suck back vapours to relieve the pressure that builds up coz of the vapurs created in the tank.
If you fill up fast > more petrol vapour created in the tank > more petrol vapour(which you already paid for) being sucked back!!
When you fill slow, less vapour is created >the pressure does not increase > petrol stays in tank!


C.

kippy

Some similar stuff here:
http://www.gassavers.org/showthread.php?t=7022

This could be a job for "mythbusters". (http://dsc.discovery.com/fansites/mythbusters/mythbusters.html)


There was an email that went around a few weeks ago with tips to save money on fuel, I think a few of them were very obviously correct while the rest could be questionable (like filling the tank slowly)
Kippy

Wertz

Unregistered. wrote: »

.... the problem of getting more mileage from one company's petrol that another's could be part of a more sinister conspiracy..(fiddling with the pumps so you get less, or that it pumps out the very minimum tolerance in the inspection standard!)

I've experienced some deviations in the distance I get on the same amounts of fuel bought from different stations and always had a suspicion that this might be the case...the same places would have had the cheapest rates at the time of the crazy fuel prices mid summer 08, so you were arguably getting a little more fuel, but didn't seem to get as much range from the fill.
Anyone any idea how often stations have their pumps inspected by the relevant weights and measures authority? Are pumps easily tampered with to this end? Or was I imaginging it, or merely using more fuel due to drving style, etc...

Unregistered.

Wertz wrote: »

I've experienced some deviations in the distance I get on the same amounts of fuel bought from different stations and always had a suspicion that this might be the case...the same places would have had the cheapest rates at the time of the crazy fuel prices mid summer 08, so you were arguably getting a little more fuel, but didn't seem to get as much range from the fill.
Anyone any idea how often stations have their pumps inspected by the relevant weights and measures authority? Are pumps easily tampered with to this end? Or was I imaginging it, or merely using more fuel due to drving style, etc...

I think they are "synchronized" so that they deliver the right amount but the guidlines would have their tolerence limits!

For example:

A pump reads that it has delivered 10 litres. So the amount of petrol that came out should be 10 litres.
However, there is tolerence of 5%. So that means, anything between 9.5L-10.5L is acceptable.


Just an example, not 100% sure of what the tolerance is.

Wertz

I'd have said that the tolerance would be a lot less than that myself...I know years back the department with responsibility for control of weights and measures were fairly stringent about checking spirit optics in pubs, the counterweights for old weighing scales, etc, and their tolerances would have been much lower...they also would have doled out hefty fines and/or moved against renewal of your trading license for repeated breaches.

Ta me anseo

mike65 wrote: »

Cold fuel is denser so more will fit in the tank (but it wont be any cheaper!).

Mike

Almost every single petrol station stores their fuel underground where the fuel temperature almost never changes and when it does, it changes veeeerrrrrryyyyyy sssslllloooooooowwwwlllllyyyy, so filling up in the morning makes no difference to the density you're getting!!!

Even if you left petrol outside in a big bucket, the kind of quantities that are involved in petrol stations would take an age to drop in temperature any appreciable amount. (I remember my Physics lessons after all! - Specific Heat Capacity how are ya!!!)

Cool Mo D

Unregistered. wrote: »

Hey jen!
I like the idea of the urban myths, heard them myself, but i can "demythify" them if you like!...

Some companies petrol differ in that some offer petrol with a higher octane rating. This means that engine knocking is reduced, making it more effiecient! but if they're all selling the same bog standard 95octane(or 98?) then it should be all the same.... the problem of getting more mileage from one company's petrol that another's could be part of a more sinister conspiracy..(fiddling with the pumps so you get less, or that it pumps out the very minimum tolerance in the inspection standard!)

Regarding filling up in the morning... Well, the idea was clever.. petrol would be denser in the cold than in when it's warm. So you would get more(mass-wise) in a litre! However!! The petrol is stored underground, where the temperature change would be a lot less than it is on the outside. So even though the air is cold, the temperature of the petrol may have only changed by 1 or two degrees.
I have also heard that modern-day pumps will self-adjust based on the petrol temp, to ensure the same amount of petrol each time!

I have a good tip so you get more mileage! Don't let your tank get too much below halfway before filling! When you have a low amount of fuel in the tank, it will be easier to vaporise in the tank (due to it being easier to heat up from the air temp coz there is less) and the more empty space you have in the tank, the more the petrol will vaporise to fill the space. Now the fuel gauge doesn't read the amount of petrol vapour their is, and it will tell you that you need to fill up!
So when you keep more petrol in the tank, it requires more energy to become a vapour which it cannot get from the air temp!


EDIT: Filling the tank slowly!! I think you benfit from this for two reasons: because it does not stir up the petrol from the resevoir as much as fast-filling. Thus meaning the grit wont be disturbed to much and wont go into your tank.
the second way, is down to the pump's clever little design. It is designed so that petrol flows out of it into your tank, AND to suck back vapours to relieve the pressure that builds up coz of the vapurs created in the tank.
If you fill up fast > more petrol vapour created in the tank > more petrol vapour(which you already paid for) being sucked back!!
When you fill slow, less vapour is created >the pressure does not increase > petrol stays in tank!


C.

This is sorta nonsense.

When your petrol tank is full, there is only a small space for vapour at the top of the tank, so a small amount of petrol vapour coming from your tank. When your tank gets empty, the empty space where the fuel was will indeed fill with petrol vapour.

Now for the sciencey bit.
The amount of vapour in your tank depends on the vapour pressure of the fuel. This depends pretty much only on the temperature of the outside air, and yes, contrary to what is written above, the petrol does get the energy to vapourise from the air.
Now, does this mean you should fill up fast or slow. There are two factors at play here.
Firstly, the petrol does not evaporate instantaneously. So if you fill up quickly, the petrol will have less time to evaporate out of the tank before you put the cap back on. But all the splashing of the liquid on a fast pour may cause a few droplets to splash out of the tank. And that's about the lot of the amounts that you're talking about, a few droplets. No matter what way you fill your tank, it will make basically no difference to how much petrol you get from the pump.

Oh, and the reason that the pump sucks in air at the front is so the auto shutoff on the pump can operate, not really to suck in vapour from the tank. Petrol tanks can breathe on their own, through vent lines.

Alun

Ta me anseo wrote: »

Almost every single petrol station stores their fuel underground where the fuel temperature almost never changes and when it does, it changes veeeerrrrrryyyyyy sssslllloooooooowwwwlllllyyyy, so filling up in the morning makes no difference to the density you're getting!!!

True, plus the coefficient of expansion for petrol is only 0.00095/degree Celsius, so a rise of a few degrees will make bugger all difference anyway.

Cool Mo D

Alun wrote: »

True, plus the coefficient of expansion for petrol is only 0.00095/degree Celsius, so a rise of a few degrees will make bugger all difference anyway.

Also, it's a bit misleading to say that petrol is sold in volume, so the density changes affect how much you get. Petrol is sold based on a litre at 15 degrees C, and pumps are supposed to autocorrect for temperature.

pred racer

I normally wouldnt have any time for these sort of stories.......but I work in a large company and so many of my work collegues have said that they dont get as good milage out of tesco petrol. they cant all be imagining it.

having said that, its always a statoil truck I see filling up the tank, and I never hear anyone giving out about statoil/topaz petrol

I drive a diesel and have never noticed any difference!!

Loveless

I remember a guy telling me that when he used to get his petrol, in a small town with a bit of a hill, he would always get an extra litre or two in if the car was pointing up the hill rather than pointing down the hill

The_Conductor

Westmeath Lass wrote: »

Cilit Bang ?? Are you serious ? :eek:

You'll get a decent fuel cleaner in Halfords for 2-3 Euro which is supposed to clean the heads etc and make the burn cleaner- and thus more efficient. There are different petrol and diesel versions- I'll definitely vouch that after the diesel cleaner there is a lesser amount of exhaust smoke (aka a cleaner burn)- I'm not so sure about the petrol cleaner.

Someone mentioned putting a litre or two of parafin oil every second fill- is that another myth? Don't see why not?

Re: Topaz- I've had a few problems with 'dirty' fuel there- it was explained to me by the mechanic who cleaned out the tank that it looked like crude oil? Mind- this was months ago- before their 'clean fuel' campaign. Perhaps I got the bottom of the reservoir when I was filling up?

maclek

http://www.snopes.com/inboxer/household/gastips.asp

The bottom line is that there are much easier and better ways of improving the efficiency of your car (and thus of saving you money at the pump) than the tips outlined above. Particularly important is proper maintenance, including engine tune-ups, wheel alignments, tire pressure checks, and filter replacement. Mileage can also be improved by removing from the car little-used equipment that adds weight or increases drag (e.g., sporting gear, tools, roof racks/carriers). Driving habits are especially important: jackrabbit stops and starts eat up extra fuel, as does driving at higher speeds. All in all, the simple habit of engaging in planning and combining multiple trips into one excursion will likely save the average motorist far more money (and time) than all four of the above tips combined.

Note also there are no vapor recovery systems on pumps in Ireland, so the idea of pumping slowly doesn't apply.

Bandara

MYOB wrote: »

I would presume - but could find no info on the flyer or website - that Topaz "Clean Unleaded" is E5, just like Maxol and many others sell.

All fuel meets basic quality standards, most of it comes from common sources. Individual retailers may use different additives to other ones; and theres the difference of E5 vs. 'normal' 95RON...

In general, I've found I get the worst mileage by a noticeable amount off Tescos, but their station is filthy and poorly maintained so this may cause it more than anything else for all I know.

Topaz Super McDuper Cleany Weeny Fuel (tm) is complete horsesh!t

I get the same deliveries from the same place (ie same gantry in the depot) as they do, quite often I take half loads from a tanker that they couldn't take delivery of. Smoke and mirrors to fool the masses, we all pretty much sell the same thing

Anan1

Loveless wrote: »

I remember a guy telling me that when he used to get his petrol, in a small town with a bit of a hill, he would always get an extra litre or two in if the car was pointing up the hill rather than pointing down the hill

That one is actually quite possible, filling on a slope could trap air in the tank.:)

Seth Brundle

Loveless wrote: »

I remember a guy telling me that when he used to get his petrol, in a small town with a bit of a hill, he would always get an extra litre or two in if the car was pointing up the hill rather than pointing down the hill

Are you trying to suggest that he was getting more for his money or just that parking on a slope meant that he could brim it more?

zilog_jones

I've tried the slow pumping thing the last few times I've filled my car - not surprising there was no discernable difference in fuel economy. It's got worse if anything, but I noticed my tyres had all gone down about 3-4psi since I last checked and it's been about 6000 miles since I last got the oil changed...

c-note

PETROL is sold volumetrically i.e. by the litre.
but its energy content depnds on its mass (kgs)
you'll get more mass per litre when its colder (better value)
and less mass per litre when its warmer (worse value)
but the underground tanks in a station are kept at constant temp (or close enough to make no difference)

as far as PETROL QUATLITY:
YES petrol comes in varying qualities, but it dosnt make any diff to you're mpgs, i think there may be a minimum octane number of 92 in ireland (could be wrong on this) but 95 is normal, (not like in usa where i think you can get 85).

In short i'd be far more concerned with how accuratly the pumps are calibrated. if i'm selling you petrol for 98c/L but my "litre" is only 970mls then thats really 101c/litre

Cool Mo D

c-note wrote: »

PETROL is sold volumetrically i.e. by the litre.
but its energy content depnds on its mass (kgs)
you'll get more mass per litre when its colder (better value)
and less mass per litre when its warmer (worse value)
but the underground tanks in a station are kept at constant temp (or close enough to make no difference)

as far as PETROL QUATLITY:
YES petrol comes in varying qualities, but it dosnt make any diff to you're mpgs, i think there may be a minimum octane number of 92 in ireland (could be wrong on this) but 95 is normal, (not like in usa where i think you can get 85).

In short i'd be far more concerned with how accuratly the pumps are calibrated. if i'm selling you petrol for 98c/L but my "litre" is only 970mls then thats really 101c/litre

True, and petrol pumps correct for temperature too, so you get a "standard" litre of petrol. The standard litre of petrol is based on a temperature of 15 degrees, so pumps correct to the equivalent amount.