The real 50% of a fuel tank?

[Supervinnie40]

I've been monitoring my fuel consumption since I got the car. And I discovered that I can average of +/- 650km with one full tank of petrol (I've got a 1.8 non-turbo).
Since (according to my papers) the fuel tank is about 65 liters, this would mean that I'm doing an average of 10km for every 1l of fuel (which sounds about right since I drive a lot around town and not so much on the highway).

So, one would assume that 65 liter would mean that the needle is all the way up. Which it is.
32.5 liter would then be displayed as the middle between the highest point and the lowest point (50%). At this point I should've done about 325km.
10 liters would probably be displayed as roughly 1 third of the middle and the lowest point. At this point I would have done about 550km.
Sound right... right?

But it isn't.
When I've driven 325km, the needle is at roughly 65%. (roughly 10km per %)
When the needle is at 50%, I've driven roughly 500km. (roughly 10km per % difference)
When the needle is at 75%, I've driven roughly 600km. (roughly 40km per %)
(100km just made 25% difference)
When the needle is at 0%, I've driven between 650 and 750km. (between 20km and 60km per %).

In short, it seems that the first 50% of the fuelgauge go slower then the last 50%.
Not real news, as far as I remember this has been the same with every care I ever had. But I'm wondering if there is an explanation for this?

I have owned a Hyundai Atos for a while, and the mechanic told me that the shape of the fueltank means that there is less full in bottom then in the top, because the bottom is smaller then the top. But the fuelgauge doesn't take that into account. Which causes the fuel gauge to give the impression like you have 50% left of the amount of fuel in the tank, but it actually shows you that the level of fluid is at 50% of the maximum height of the tank.
Which is something completely else.

Anybody knows a bit more about this?

[clf]

The fuel gauge also moves up and down depending on how heavy your right foot is too. It appears to be linked to the economy indicator and range. I ve seen mine go up as the car has warmed up and started to cruise.

[Andydote]

My fuel gauge goes up when I make a hard right

[Supervinnie40]

Originally Posted by clf

The fuel gauge also moves up and down depending on how heavy your right foot is too. It appears to be linked to the economy indicator and range. I ve seen mine go up as the car has warmed up and started to cruise.

That could be something that only the MG (or Diesel) has. I don't have an economy indicator.

Originally Posted by Andydote

My fuel gauge goes up when I make a hard right

That could be because of the location of the sensor

[championdaddy]

The top of the fuel tank is larger than the bottom.

[chris75]

I don't think they are very accurate ................

[James.uk]

The bottom of the tank has a huge *dent* in it where the drive shaft goes on rear wheel drive cars. (V8) so it holds less fuel in the lower section. The in tank pump feeds the fuel from one side to the other at the bottom..
...

[paulozy]

as the 75 uses a saddle tank, the top of the tank holds more fuel than the bottom.

[bigbaldbloke]

Originally Posted by Supervinnie40

That could be something that only the MG (or Diesel) has. I don't have an economy indicator.

I read it as the IPK display.

[SD1too]

Originally Posted by Andydote

My fuel gauge goes up when I make a hard right

Andy,

There are two sensors, one in each side of the saddle tank. It sounds as if one of yours isn't working.

Simon