Thought to do a check on my actual mpg rather then going by the trip computer,

Had a quick look around to see if anyone else had had a go at this but nothing came up for a quick search

Ended up doing the following test

When the fuel light came on i topped up £10 and made a note of mileage etc when the fuel light came on again, Did this 4-5 times over a space of a month or so to get an average and it comes out no where near what the trip computer is saying,

Wondering if anyone else has this issue?

How much fuel did the £10 buy then,

(ie, how much a litre was it?)

and how many miles did it take you.

george

Proper way to calculate is to fill to brim each time.

£10 can vary so much depending on the price of fuel

fuel cost: 136 per litre

filled: £10

miles covered: 57-60

car says around 50mpg

calculation says: 35mpg

These were short journeys and i know the mpg is bad with them, however i would still expect the trip computer to give a closer estimate

Get on Fuelly.com, dead handy for logging and comparing your all time fuel usage. It'll even produce graphs to show your mpg over time. You just need to reset your trip computer after each fuel up then write down how many miles you covered on the receipt before you reset it, all the other info you'll need is on the receipt.

You can get the free app to log it on the move, I cannot condone that you use it on the forecourt though

The problem with calculating one tank is there are so many variables. My graph is anything but a straight line. It's also handy for fault finding if you see an unusual and consistent drop.

Edited 15 May, 201313 yr by Ben90

Your method of calculation is seriously flawed!

So was it 7.3 litres you put in?

george

Your method of calculation is seriously flawed!

How so?

So was it 7.3 litres you put in?

george

Sounds about right, These were calculated on a couple of apps/sites

Only proper way is to brim the tank every time, this is what I do.

Over 5, 715 miles / 596.40 litres my average is 45.76 mpg.

13.8p a mile and a £1.38.9 average cost per litre.

I really couldnt give a toss about MPG any more as long as its near 480-510 a tank i'm a happy bunny

How so?

Going up a hill can bring the fuel light on or round a corner. As already stated - the only close to accurate method is to brim the tank and then do the calculations based on another brimmed tank

Ill give that a blast, and see what it does, the route is quite flat, plus the light doesn't turn on when on an incline and then off when not,

Just been having a look a Fuelly now, cheers for info

I really couldnt give a toss about MPG any more as long as its near 480-510 a tank i'm a happy bunny

Wish I got those miles to a tank lol, don't do many long runs though..

And OP, trip computer always lies anyway.

Going up a hill can bring the fuel light on or round a corner. As already stated - the only close to accurate method is to brim the tank and then do the calculations based on another brimmed tank

The problem with figures like this taken in isolation is fill variation due to air locks and venting. My lifetime mpg is 41.x, using vented fills I've had it as low as 30 and as high as 55 so I'd suggest the above but average it over several tanks. My vented to unvented figures almost always are bang on average.

For the op it's been discussed in most mpg threads, you measure distance in miles and fuel in liters, you don't measure £10 of fuel as the fuel value changes, from day to day and garage to garage, the sender is also not a fixed point of reference as pointed out. Also your sample size is way too small to get an accurate figure, small variations on £10 worth will have a massive impact on your figures.

Avalon can you explain what you mean by vented/unvented?

In the neck of the fuel filler on the right hand side you will see what looks like a small bolt. When filling up you can push it with the nozzle of the fuel pump - this vents the expansion tank and allows it to fill up with fuel. It allows around 10 litres of extra fuel to be pumped in = vented fill

Edited 15 May, 201313 yr by Brun747

Thank you Mr Brun.

I do that most fills anyhoo

Fill up, drive 100 miles ish, fill up, then do your maths.

For me over the last few vented fills (£70) morrisons diesel at 136.9, 51ish litres, ive got 400ish miles give or take a few. Which calculates to 35mpg aswell...

That's bad! What you running? I get 36-38 mpg out of a 330d!

that does sound bad, if i thrash my car i get 45 plus mpg and mine is standard.

For me over the last few vented fills (£70) morrisons diesel at 136.9, 51ish litres, ive got 400ish miles give or take a few. Which calculates to 35mpg aswell...

I'd put that down to Morrisons fuel, that said i've only used Asda here. [We dont have Morrisons in N. Ireland any more]

I've had issues in past cars with Morrisons fuel from Ayr when i'm over in scotland bringing on EMLs and APS on a 207.

Try filling up a few times with decent petrol from BP or Shell [Which we also dont get over here any more :(]

Also mine give poorer mpg when its due a service

I'd put that down to Morrisons fuel, that said i've only used Asda here. [We dont have Morrisons in N. Ireland any more]

I've had issues in past cars with Morrisons fuel from Ayr when i'm over in scotland bringing on EMLs and APS on a 207.

Try filling up a few times with decent petrol from BP or Shell [Which we also dont get over here any more :(]

Also mine give poorer mpg when its due a service

Assuming he is running a stock VRS 35mpg suggests an issue with the car not the fuel. Between our 2 VRS's over 190k miles between them I have never seen less than 43 mpg with fuel used from all suppliers!

Miles travelled divided by litres to fill tank times 4.545

12413 / 1017.65 x 4.545 = 55.44 mpg