Xsara Picasso 1.6HDi erratic fuel guage?

[xsara92]

Are the fuel level sensors on Citroens of this sort of age likely to be completely unreliable?

I filled up with diesel today. The low fuel warning light was on, but the tank would only take 40 litres, which means there must have been 20 litres in there!
Unless, fuel quality can influence the sensor reading somehow?
Of course, consistent with the light, there was only one bar left of eight on the display.

In the past, however, I once filled 57 litres when there was one 'bar' left, but the lamp had failed to come on.

My only concern is that if I developed a serious engine fault and fuel economy dropped drastically, it might not be registered and I'd have a breakdown on my hands..

[GiveMeABreak]

No, but running low fuel levels all the time is going to bugger about with the fuel level sensor as it's going to get thrashed about without much fuel in the tank.