mpg head ache

Gritty

Gritty

Member
Hi folks

Im a little confused re my mpg can any one help please?

I notice the fuel gauge needle moves swiftly down wards on my tdi 75 so assumed I had a fuel problem until I found this site.

www.terrycassell.com/mpg-calculator/index.php

It cost me £29.30 to fill up, thats £23.84 litres of diesel at £1.22 per litre

I got 320 miles before the orange fuel light came on. Type the above into the calculator and it claims Im achieving 60mpg I think??

What I cant understand is why the car is only taking approx £30 to fill up ie 24 litres when its a 35 litre tank?

Are the calculations above correct and does any one know why my car only accepts 24 litres to brim?
 
dieselfan said:
...my 2002 with 75hp AMF engine have 6 litre left when the fuel light comes on.
Click to expand...

So could this be a fuel gauge problem ?

I put 24 litres in cos my fuel light is on but the tank has up to 10 litres in it already if that makes sense?
 
are you sure that it is full with 24 litre from fuel light coming on
i.e. does the gauge go to slightly above full, it normally takes about 25ish miles before the gauge starts to move from full
If it does this then the top end of the gauge is working correctly.
You would need to run it until the gauge was on empty i.e. for 50 to 60 miles after the fuel light comes at which point the gauge should be on the empty mark Then fill it upon and see how much it takes (should be 34 litres), but I suspect that yours will then take 30 litre, indicating a 4 litre error at the bottom of the tank.
You could replace the sender unit, but personally I would live with it and fill up about 50 miles after the fuel light comes on if you must run the tank to near empty (you will still have the 5 litres of fuel in the tank at this point)
The tank does hold a little more than 34 litre, or to be exact the piping to the tank holds an extra 1.5 litre or so, it is possible to utilise this on the TDI by pressing the little plunger in the filler neck to 'burp' the tank when it says it full, you get a little more in
Never do this with a petrol as petrol needs expansion room due to gassing

If you do go down the changing the sender unit route then ensure you get the correct sender as there are several (34 litre original, 34 litre reverse reading and 42 litre reverse reading) Only Audi could make it so complicated on a single production run that di not last that long

Cheers,
 
Fuel sender how does one get to
johnyfartbox said:
Could well be the fuel sender unit in the tank
Click to expand...

How does one get the fuel sender? is it a tank off job
depronman said:
are you sure that it is full with 24 litre from fuel light coming on
i.e. does the gauge go to slightly above full, it normally takes about 25ish miles before the gauge starts to move from full
If it does this then the top end of the gauge is working correctly.
You would need to run it until the gauge was on empty i.e. for 50 to 60 miles after the fuel light comes at which point the gauge should be on the empty mark Then fill it upon and see how much it takes (should be 34 litres), but I suspect that yours will then take 30 litre, indicating a 4 litre error at the bottom of the tank.
You could replace the sender unit, but personally I would live with it and fill up about 50 miles after the fuel light comes on if you must run the tank to near empty (you will still have the 5 litres of fuel in the tank at this point)
The tank does hold a little more than 34 litre, or to be exact the piping to the tank holds an extra 1.5 litre or so, it is possible to utilise this on the TDI by pressing the little plunger in the filler neck to 'burp' the tank when it says it full, you get a little more in
Never do this with a petrol as petrol needs expansion room due to gassing

If you do go down the changing the sender unit route then ensure you get the correct sender as there are several (34 litre original, 34 litre reverse reading and 42 litre reverse reading) Only Audi could make it so complicated on a single production run that di not last that long

Cheers,
Click to expand...


Hi Paul

When the light came on I filled her up to the top pump nozzle clicked twice at £29.30, 23.84 litres and yes I would say it did about 20 ish miles before fuel gauge needle started to fall.

I got 280 miles approx before fuel light came on then ran for another 40 before filling up again.

Filled up again to the brim 26.33 litres £32.89

How is it possible to test my mpg if I have no real idea about how much fuel I ve used?

I need to run it to empty then log mpg, fill up and run to empty, log mpg.

Just as a matter of interest what problems would I encounter running out of diesel?
 
No no that is not the way to check mpg
Full car to brim and zero trip
Drive around as normal until you need to fill up either when fuel low light comes on or before
Ideally go to the same filling station and the same pump but this just makes it more accurate and fill up to brim again
Note the number of litres and convert to gallons
Take the trip reading of miles traveled and divide by the number of gallons and this is your mpg for that tank
If you keep doing this and add the miles from one fill to the next to the next and add the gallons used from one fill to the next to the next you will get a more accurate mpg figure

I would avoid running out of fuel as it will take some engine cranking to bleed the air from the fuel system after you put fuel in the tank plus there may well be crap in the bottom of the tank that would get pulled into the filter etc

Cheers


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Have you tried calibrating (resetting with a full tank) the gauge with VCDS?

RAB
 
Thanks for the advice.
depronman said:
No no that is not the way to check mpg
Full car to brim and zero trip
Drive around as normal until you need to fill up either when fuel low light comes on or before
Ideally go to the same filling station and the same pump but this just makes it more accurate and fill up to brim again
Note the number of litres and convert to gallons
Take the trip reading of miles traveled and divide by the number of gallons and this is your mpg for that tank
If you keep doing this and add the miles from one fill to the next to the next and add the gallons used from one fill to the next to the next you will get a more accurate mpg figure

I would avoid running out of fuel as it will take some engine cranking to bleed the air from the fuel system after you put fuel in the tank plus there may well be crap in the bottom of the tank that would get pulled into the filter etc

Cheers


Sent from my iPhone using Tapatalk
Click to expand...

Ok I will give this a go.

Thanks for your advice.
 
depronman said:
No no that is not the way to check mpg
Full car to brim and zero trip
Drive around as normal until you need to fill up either when fuel low light comes on or before
Ideally go to the same filling station and the same pump but this just makes it more accurate and fill up to brim again
Note the number of litres and convert to gallons
Take the trip reading of miles traveled and divide by the number of gallons and this is your mpg for that tank
If you keep doing this and add the miles from one fill to the next to the next and add the gallons used from one fill to the next to the next you will get a more accurate mpg figure

I would avoid running out of fuel as it will take some engine cranking to bleed the air from the fuel system after you put fuel in the tank plus there may well be crap in the bottom of the tank that would get pulled into the filter etc
Click to expand...

+1 for this, definitely the final paragraph - running out of fuel on a car as old as this will just drag up the detritus from the bottom of the fuel tank and block up the fuel lines (think of a smoker's arteries and you won't go far wrong).

I use the "fill to brim" method on my cars, and then log them on Fuelly.com (see my signature below for link) this indicates an average of 60.4mpg average (currently) though my record I believe is 74.9 for a tankful.
 
I was going to suggest fuelly too - I’m only at 52mpg average. Best 56.7. It is cold up here!


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My TDi 75 has bested at 57 and averages about 54 not as much as I’d like but can’t complain really!


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Pinkythelabrat said:
I was going to suggest fuelly too - I’m only at 52mpg average. Best 56.7. It is cold up here!
Click to expand...
Cenick said:
My TDi 75 has bested at 57 and averages about 54 not as much as I’d like but can’t complain really!
Click to expand...

It definitely depends on your journey - since I changed work a few months ago I would say my average has been about the 57 mark, but I'm getting stuck in lots of traffic these days, whereas before there was lots of long journeys at 50-70mph without stopping.
 
I've been getting 51mpg(not complaining). I'd like more though much of my driving is shorter stop start which doesn't help. Longer runs will improve if I can stay off the boost, thanks Paul. :D
 
damadgeruk said:
I've been getting 51mpg(not complaining). I'd like more though much of my driving is shorter stop start which doesn't help. Longer runs will improve if I can stay off the boost, thanks Paul. :D
Click to expand...
that is always the challenge with a remapped engine
 
you are likely right my friend, but I developed the remap for my own purposes, then decided to offer the many hours of work to others that could make use of it.
I must admit to the odd smile directly associated with the 2nd / 3rd / 4th gear acceleration particularly when overtaking something that the A2 should be be overtaking :)
 
Cenick said:
My TDi 75 has bested at 57 and averages about 54 not as much as I’d like but can’t complain really!


Sent from my iPad using Tapatalk
Click to expand...

Well what a numpty!

Just checked Fuelly settings and realised that it defaults to US gallons, when I altered it to Imperial gallons my average has now increased to 64mpg with a best of 68.5


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