I was always under the impression that the fuel gauge and MaxiDot were fairly accurate.

Well how wrong could i be.

I just recently drove 540 Miles on a full tank. (all of it autobahn apart from 3 miles at start) I got the 540 miles before i got the first hiccup from the car which signals you are about to run out of fuel.This is were i promptly pulled over and filled up with my 10 litre petrol can that i keep in the boot.

Now firstly i Filled the tank up as much as it would take but didnt brim it. Got 58.4 litres in the tank

Set off driving down to Bavaria. Now for the for the first lie. Culprit Fuel Gauge:mad:

The fuel gauge didnt budge an inch for 157.3miles according to the trip. Then by the time i got to 200 miles id used a quarter of a tank (which in theory should mean 800miles from a tank ...... i wish)

Next lie Culprit Maxidot:mad:

The Maxidot said i was doing an average of 63Mph (even though i stuck between 70-80)

Then it said i averaged 36.4MPG for the journey. However using the calculator on this website Golders Miles Per Gallon Calculator .:. MPG - UK / £ it says i average 42.03 MPG and i got the same answer using a calculator. Dont get me wrong im not complaining i think thats outstanding for a vRS:thumbup:

Last Lie Culprit MaxiDot:mad:

The Range said i had 0 miles to go and i did 34.2 before i got a hiccup

So Beware dont rely on your maxidot or fuel gauge. :P:P

Carl:thumbup:

but surely its like relying on your sat nav??

(you dont)

The fuel gauge didnt budge an inch for 157.3miles according to the trip.

Its the shape of the tank and the amount of fuel you put in. Had you put the 55L in thats the official capacity it would have started from full properly and not gone off the scale (assuming you had a completely empty tank to start with). The reason the gauge didnt move was because it cant move any higher than full.

The Maxidot said i was doing an average of 63Mph (even though i stuck between 70-80)

The maxidot is more accurate than the speedo, typically at 70MPH you are in reality doing somewhere just over 60MPH, whilst at 80MPH you are really travelling at 70ish.

The Range said i had 0 miles to go and i did 34.2 before i got a hiccup.

Thats because you entered the tanks reserve, the maxidot is typical of all fuel computers. It runs down to zero, slightly early to give you some hint that now maybe a good time to fill up. If you did really run out at zero, and you had left it to long with no garage nearby you would be fooked.

The Range said i had 0 miles to go and i did 34.2 before i got a hiccup

you also have to be aware of how a trip computer calculates remaining miles... imagine you are designing such a system - the distance left is the amount of fuel * the miles per gallon... but what measure of 'miles per gallon' should you use? Using instantaneous is no good, the 'remaining distance' would fluctuate up and down every second.

So, you need to use some kind of average - but what average? Over the whole journey? Over the last mile? A car will typically take an average over the last 10 miles and then apply this to the remaining fuel to calculate distance left. At best this is only ever an estimate - and it is easily wrong if your fuel economy has changed during that 10 mile period. It is very easy to get the trip computer down to, say, 20 miles left and then drive another 20 very carefully and for the distance left to go UP!

This is nothing to do with a lie or inaccuracy in the computer, simply that no one has yet invented a crystal ball that will tell the car what driving style you are going to use for the remaining distance.

(ps. I don't know whether the octy uses 10 miles or not - that's what volvo use)

i remember a mercedes sprinter we had once, soon as it reached zero on the fuel gauge the fuel light would come on and then it would cut out as it was empty, no reserve or you do 10 miles on red, when it went it went.

Maxidot is an ar$e when it comes to how many miles you have left in reserve....

They are all much of a muchnesss on any car, there is a tolerance built in to allow for idiots who drive past 3 or 4 garages until they reach their car's favourite watering hole (me).

I always thought the reserve was in fact the red section on the gauge which can also be marked "R". Entering the fuel tank reserve is usually followed by the Fuel light. IIRC it's 8 litres on the Octavia.

My fuel light usually comes on at about 75-80 miles range, this is in fact the start of the tanks reserve.

so the 58 litres the tank holds, does that include the reserve?

The official figure is 55 for standard 2 wheel drive and circa 60 litres for 4x4 models including the reserve, the higher filling figures quoted probably include the filler neck.

I have filled up with about 56 litres with a range of 30 before.

ive been as low as 10 miles left and filled up with 54 litres.

I would imagine the range calibration is different for petrol and derv engines due to fuel consumption

The most annoying factor is that I can fill up (around 50litres) and the Fuel distance will say 530 miles.

At the time of filling the average mpg will be reading 42mpg.

how come that when i have done 380 miles "trip" do i get the request to refuel

somethings not quite right ?

Doesnt sound right.

I usually get a range of 550 and I get the fuel light at about 460 trip.

I know you can recalibrate the fuel consumption/range via VAG-COM but I haven't tinkered with it myself.

I do have the 140 DSG

I had another look at it last night when I got home.

Trip 180

Fuel Left 345 miles

Average 42mpg

Then this morning when I got to work

Trip 195

Fuel Left 340 miles

Average 47mpg

I can't work out how at this stage it thinks there's 340 miles left in the take at 40+mpg - add this to trip of 195 = should get 535?

I can guarantee the fuel 'bong' appears at 380 miles trip.... i may get 420 total (with reserve tank)

The range is calculated from the average mpg over the last 50Km (approx 31miles). This average could be very different from the trip as a whole.

The Fuel warning light comes on when you have 8 litres (about 1.8 gallons) left. So if you average 42mpg the light comes on when you have a range of 75miles left.

On my 1.9Tdi it generally comes on with 90- 95 showing on the range.

Checked the computer again last night

Trip 270

Fuel Left 215 miles

Average 43mpg

Total mileage to tank now 485

When i arrived at work this morning

Trip 284

Fuel Left 210 miles

Average 42mpg

Total mileage to tank now 494

I still think that it will request a fill up at the 380 trip mark