Oil control lamp and temperature variation

Hello all, my LUPO 1.4 60PS BJ 2001 (AUD) causes problems that I can’t fix. If the engine is warm and only when driving, not in the stand, the oil control light goes on and beeps. It beeps a few times and lights up. At some point it starts by itself, but after a few minutes the whole thing repeats itself. The temperature in the engine varies between 90 and 80 degrees. So it always peels off and then the oil control light goes on. Oil is enough. Oil separator has already been changed. Oil is new. Does anyone know what it might be?