You can not drain all of the oil out of the engine, there will be about a 1/2 quart that remains in the engine after it quites draining. If you add 4 quarts, the dip stick will show that the engine has been overfilled, and you do not want to do that. Look at the manual again, it explains this. If the engine has been diassembled, cleaned and dried out, that is a dry fill and takes 4 quarts. A plain drain & fill (normal oil change) is called a wet fill and takes 3-1/2 quarts.