Fuel gauge accuracy

[David Lewis]

I filled up my car with fuel on the first day and naturally over the last 11 days I have been driving the car around. Today I got the warning to refuel as I has only 45 miles worth of fuel in the tank. I expected to have to buy around 50 litres but I only put in 42. That must mean that there were 13 litres left in the tank or put another way around a quarter of a tank full. Given that I had driven some 480 miles I could probably have gone a lot further than the 45 miles suggested.
Any one else get similar results?

 

[Talk-torque]

The range reading is based on your current, instantaneous, consumption, so if you check it when you are clogging in second you will get a lower figure than cruising in top with a feathered throttle. You can get it to increase significantly by driving economically. It doesn't change quickly and goes in jumps of 5mpg. You must have caught it at a bad time!

 

[DavidB]

I have had my "new" Golf (1.4 petrol,122ps, DSG) for about 11 months now and on a number of occasions have noted a significant "non linearity" in the readout.
After completely filling it, I can do about 200 miles on the first quarter of a tank, i.e. down to the 3/4 mark, then for each following quarter I get about 100 miles each, thus getting about 500 miles on a tankful.
Anyone else getting similar results ?

David

 

[Evil Dan]

I expected to have to buy around 50 litres but I only put in 42. That must mean that there were 13 litres left in the tank or put another way around a quarter of a tank full.

It has a 50 litre fuel tank (but I usually get around 52 litres in when it is almost empty).

 

[meridion]

Its to do with the mechanism for reading fuel levels in the tank. It has a float in there, and if you fill the tank full, while the float is submerged in fuel, all the way to the bottom of the float, it barely moves (and looks like you're getting more mpg then you actually are, and then all of a sudden it drops more rapidly.

http://auto.howstuffworks.com/fuel-gauge1.htm

 

[DainBramaged]

The tank staying on full for a while thing happens on most cars. You think "oh i'm getting great consumption...I've gone 80 miles and it's not moved", then it starts to drop quickly lol. As meridon has mentioned, it's to do with the float in the tank, plus if you really brim it, extra fuel sits in the pipe between the filler cap and the tank - it's probably only a liter or two, but it still adds up.