Pondering a puzzlement? I will never over fill the tank and I will always keep the oil at the proper level with that said here are my questions. There are two lines coming out of my oil tank on 2003 Heritage Softtail Springer. These lines are for siphoning the oil out and for returning the oil to the tank. The engine only takes the amount of oil that is needed to lubricate and cool the engine (a preset amount of oil). I know that one is not supposed to over fill the tank. My question is what harm can it do to over fill the tank? The pump only takes out what it puts back and there is always the same amount of oil circulating in the engine regardless of the amount in the tank (as long as there is enough oil in the tank). I know I am wrong somewhere in my thinking but I cannot figure out how it can harm the engine. The only stupid questions are those that are unask!