Thank you.Up tends to intensify or indicate that the action was complete in its effect/done to the maximum extent: compare,
He filled the car with petrol. -> Used to indicate that he put petrol in the car, but, unless otherwise indicated, it does not mean to the maximum capacity.
He filled the car up with petrol. -> Used to indicate that the car was filled to the maximum capacity. (Also intensified further as in: "He filled the car right up with petrol.")