Yes, they fill if you don't empty them, but if you do empty them then you only fill till 7700ish (I don't remember the exact number, what the harrier holds internally). The MFD shows no fuel gain past the 7700ish. Now if you don't drain them before contact it seems to fuel everything up just fine. However there still seems to be weight gain from invisible fuel that is not actually there leading to the problem I originally stated. This is with inboard tanks, I haven't tried any other variation/placement.