if you have your parts blasted,Ospho won't work will it. i have some of it and it does nothing to clean metal, it has to have iron oxide to make the chemical reaction happen. stuff thats covered with surface rust it works great, turns rust into like plasticoat,but it has to have the rust to work according to the instructions you supossed to only remove the scaly rust and leave the surface rust so it can make the reaction hapen.
i have put it on a part that was clean metal once ,the part had some water droplets on it and had ran down its side and it had rusted in that pattern and it was pokadoted when i put the ospho on were it was clean metal was still just clean metal,so i read the instructions which said it needed the rust to work,