fuel gauge malfunction

Greetings

I just bought the vehicle. diesel. It is not 4 months, I do not have the opportunity to experience it because I can not spend a lot of storage.

When I completed the vehicle, the first two tanks went around 800-900 km.

In the 3rd warehouse, the pointer was left in the middle, although I made 570 km, the pointer was left in the middle. I filled it again and now 530 hands are halfway. How can I handle this problem in a convenient way.

note: once he was putting gasoline he pulled 3 liters until he noticed the pump, we completely drained and cleaned the tank with air, could there be something, the pointer may have slipped

have the float checked, then check the counter bi

When you stop the vehicle, the indicator hand goes down to 0 and when you run it again, does it go up to half, so the pointer moves?