When the hydraulic filter is removed, the reservoir will drain out thru the filter adapter. About 3 1/2 quarts will drain out and the total amount including the oil in the filter will be about four quarts. As the filter is installed vertically, prefilling the new filter before installing it will reduce the air bleeding time. Install the new prefilled filter, put three quarts in the reservoir and let it set for 10-15 minutes, this will fill and bleed the air out of the filter. Start the engine and top off the reservoir to the bottom of the metal sleeve. Set the sleeve so the hole in the side of it faces forward and tighten the fill cap. Test drive the machine and recheck the oil level.