The rod on the sender unit in the tank could be bent, POs often adjust the rod so that the float moves up and down freely, but it is often a case of getting to know your gauges and what they actually mean.
My temperature gauge reads cold when normal and in the middle when overheating, the fuel gauge has a mind of it's own bur I fill up below halfway to be sure. Never put more than 35 liters in so it could be close, but I still keep a gallon in he back just in case.