Yesterday, the fuel indicator light was on. I filled it up with 10 liters, and the gauge moved visibly.
Today, the light was on again. I fueled it up for 5 liters. No movement. Then I fueled it up for 5 liters more. No movement. The gauge is still at the same point as it was before both fillings. Light is still on.
Why does this happen? It's a Renault Master van.
(which I am borrowing on a daily basis, and need to fuel it for only the amount I drive, which typically is in the 5-10 liter range).
The gauge is made so that it follows changes in fuel level very, very slowly. This avoids that the needle moves due to the sloshing fuel on a curvy road. But since this would be confusing when refueling, the gauge recognizes larger changes in fuel level, and adjusts for them immediately.
Adding 5l is not a large enough change, while 10l is.
Just drive around for a few minutes, and you'll notice that the gauge slowly rises to the same level which it displayed directly when adding 10l of fuel in one go.
By the way, you can observe the same on looong slopes. The gauge rises/falls slowly, and reverts to the old value, when the street is straight again. I notice this often when my tank is nearly empty and the fuel warning light lights up on the slope, and goes off several minutes after.
