Like most cars VW fuel gauges are conservative, they show pessimistic fuel levels and understated range to empty. Polo's have rather flat and wide fuel tanks so the fuel moves around under cornering, braking and acceleration which changes the fuel gauge reading quite a bit. Fuel gauges aren't instantaneous in their response, they have a lot of dampening so that the sloshing around doesn't make the gauge move. As a result of all of those factors there is quite a bit of "safety margin" built in, VW don't want us complaining that the car stopped, out of fuel, when the gauge said 10 k's to go. I have driven 20, 30 even 40 k's (on the freeway) with the range showing zero, so my guess is there's around 3 to 5 litres of "safety margin" built in.
To answer your questions, adding 3 litres is probably within the "slosh" range so the gauge simply ignored it.
Cheers
Gary
Golf Mk7.5 R, Volvo S60 Polestar, Skyline R32GTST
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