How do I work out MPG?

hardpressed

Hintza wrote: »

To be accurate you need to fill the tank to the brim and note mileage. When you next fill up brim again note mileage and amount of petrol used.

OP you are just guessing (OK might not be far away) that you have used 25l.

I filled the tank when the gauge was showing quarter full and noted the mileage and the ammount shown on the pump, then deducted that mileage from what was showing when it was a quarter full again.

diable

You cares it will soon be how far can I travel on £20 where £20 is 1 litre...........

cyclonebri1

kaya wrote: »

the brim to brim method is NOT accurate, fuel is drawn from under the ground into your fuel tank, like most liquids as it heats up it expands, which makes your reading inaccurate, also you would have to run your car until it starved of fuel to know the tank was empty both times and allow for the volume expansion due to ambient temperature, the only accurate way would be to weigh your fuel each time, which is totally impractical, the weight of fuel does not change with temperature like the volume does.

So lets keep it practical then? ;), near enough is good enough in this case, it isn't a scientific study.

cyclonebri1

hardpressed wrote: »

I filled the tank when the gauge was showing quarter full and noted the mileage and the ammount shown on the pump, then deducted that mileage from what was showing when it was a quarter full again.

Very innacurate, unless done over many fills when it will give a better indication.
Going from red light to red light will prove more accurate more quickly, but you know what could happen there.:eek:

Wig

hardpressed wrote: »

I filled the tank when the gauge was showing quarter full and noted the mileage and the ammount shown on the pump, then deducted that mileage from what was showing when it was a quarter full again.

As said, very innaccurate method to use.

Fill your tank until the pump clicks off

Keep filling more gently you will get atleast another 2 litres in.
pull the filler gun out a little so just the tip is in the hole keep filling slowly until you can see or think it it full, use a biro or something to push open the filler neck flap (if there is one) if you see fuel at the top you can stop otherwise put it back in and fill some more. Another way to do this is to fill up a 5 litre petrol can, fill your tank at the pump drive away and fill it up to the top using your petrol can slowly.

Ignore/forget how many litres you just poured in
Reset your mileage

Drive 300 - 400 miles, if you want to extend it to a more accurate 1000 miles just keep a record of how many litres you put in the tank until you do a final fill to the top.


Fill up again only this time you have to do it all at the pump. Or have EXACTLY 5 litres in your can, and repeat the process and measure exactly how many litres remain in your petrol can.

Now you know exactly how many litres you just filled up with to get you to the same level of fullness (on flat ground) and you know how many miles were travelled.


Regarding thermal expansion this can be discounted because you drive the car after filling so you create enough room for expansion without losing any petrol. You start with full tank of petrol at roughly 15C drive around 300 miles and then again fill up with petrol at the same temperature. So you know for sure that you have used the same amount of petrol that you just filled it up with. As long as you don't lose any in spillage (i.e. due to thermal expansion) you will be accurate.

Probably better to have 2 x exactly 5 litre full petrol cans, because I seem to remember once filling at the pump till full getting home and I managed to pour in a whole 5 litre can, and I still couldn't see it was full!

Kilty_2

Don't fill to the brim as much as that if you have a diesel though, you'll inevitably slop some out and cause trouble for bikers.

rockin_plumber

Hammyman wrote: »

Unbelievable. Even my 9 year old son can work that out and he's autistic.

Lets get it right. Its not that you can't work it out BUT YOU ARE TOO BONE IDLE TO.

I wish people on these forums would stop pampering to lazy people like the OP and giving them the answer.

As you have so many posts I cant believe you missed this regarding forum etiquette.... Its on the right-hand side of the screen for future reference.

Pls be nice to all MoneySavers. There's no such thing as a stupid question, and even if you disagree courtesy helps.

cyclonebri1

Hammyman wrote: »

Unbelievable. Even my 9 year old son can work that out and he's autistic.

Lets get it right. Its not that you can't work it out BUT YOU ARE TOO BONE IDLE TO.

I wish people on these forums would stop pampering to lazy people like the OP and giving them the answer.

And I supose you are a member of Mensa?

If someone asks a clear polite question, albeit too simple for you, maybe the best thing to do would be to simply not respond?, rather than making the asertion that the op is a lazy retard.:mad:

You are either here to help or feed your ego, obviously you've made your choice.

Flyboy152

C_Mababejive wrote: »

But how would you know when you had used that quantity of fuel?

When you fill up again. :huh:

dresdendave

Garetha wrote: »

Perhaps it's time we metricated ourselves, understanding Litres per 100k.

Or perhaps we should have just stuck to selling it by the gallon as we all still talk in MPG.

All selling fuel in foreign measurements has achieved is to disguise the fact that the price is now around £6 per gallon.