how to accurately check milage

For the cheapest option you could plan a postcode-to-postcode route with multimap, which will tell you how far you will drive to complete the journey, then compare it to the odometer. If this is correct then it's just a matter of filling the tank to capacity and keeping track of the miles you have driven before you fill it to capacity again, then work out how many miles you have driven with the amount of petrol you bought.

Si

The accuracy of petrol guages tends to be rubbish! My one gets empty when I have about 10 litres left. It's also effected by hills. The best way to measure it is to ask for a receipt when you fill up with petrol. The receipt will have the number of litres on it.

I don't know how accurate the odometers are, but I would expect them to be fairly close otherwise the 'number of miles on the clock' would be useless for 2nd hand cars. It will obviously vary very slightlydepending on the amount of tread on the tyres etc. Use the formula below to calculate the mpg. You weren't doing it in litres were you? If the Polo really is getting less 15mpg, then there will be something wrong with it, you should expect more than double that, or maybe tripple.

Fuel consumption = Mileage / ((Fuel used in litres)*4.546) mpg

Fill it up to the brim, note the mileage, run it near empty then fill it up again, noting the amount, and note the mileage again. Subtract the old mileage reading from the new one. Convert the litres you logged to fill it up the second time by dividing by 4.55 to give gallons, then divide that result into the mileage. This will give you a pretty accurate MPG figure. Do it several times over several tanks aggregating both fuel and mileage and you'll get a very accurate result - unless your odometer is inaccurate which isn't that likely - by much.

The message from petermcmillan snipped-for-privacy@yahoo.com contains these words:

You'd rather it were the other way round?

ok did your formula.... I fill my Punto with 40litres of petrol.... I can do bout 400miles to this; so bout 10 miles per litre... Now if I use your formula...

Fuel consumption = 400 / ((40)*4.546) = 400 / 181.84 = 2.1997

Huh??? that right?? seems awfully low

Surely you can still remember LDV fuel guages!

Divided by 4.546, not multiplied by.

Si

Take a piece of paper and a pencil.

Note mileage, and fill tank right to the top.

Drive until near empty.

Refill tank right to the top, noting how much fuel you put in.

Do the maths.

No, the formula's wrong. Should be Mileage/(fuel used in litres)*4.546 (note difference in brackets), as to convert litres to gallons you _divide_ by 4.546. Eg 45 litres is about 10 gallons, not 207 gallons as that formula would give!

So that way you're getting 400/40 * 4.546 = 45.46 mpg - perfectly respectable.

(I'm a teacher BTW including Physics to A-level...)

...But failed snipping miserably.

;)

Si

And if his odometer *is* buggered?

Si

The message from "Duncan Wood" contains these words:

I remember my wife's Metro gauge, which was the same instrument pod. She ran out of petrol so often that one day I told her that I couldn't come and rescue her because I was otherwise detained and perhaps she should plead to the Petrol Fairy in which she so clearly believed.

That was nearly 15 years ago - and she ain't run out again since.

...his fuel consumption is no longer a worry !

Point taken! Missed it that time though normally I snip accordingly.

Find a dual carriageway with big squares painted on it - The distance between them is a mile. Used to catch speeders apparently. You could check your odo this way ?

Graham

The message from "Graham" contains these words:

Or use the 100 meter posts on a motorway/dual carriageway.

-- Dave Baker - Puma Race Engines

Meters. On posts? :-) Mike.

Just curious, does anybody know how accurate the factory fitted 'in car' mpg calculators are? The cynic in me says they're bound to be more 'favourable' so we beleive them and tell all our friends how economical our current cars are, although there must be some 'policing' of there accuracy? mustent there?