You should change the oil on your lawn Boy 6.5 push mower after the first initial two hours and at the start of each mowing season. There is no drain plug on the mower so you will be draining the oil through the fill tube. Most mowing applications will require the use of SAE 30 motor oil. You can purchase the oil for your mower at any auto parts store. Most auto parts store will also dispose of the oil for you.
Place the Lawn Boy push mower on a level surface and start the mower. Allow the mower to warm up for a few minutes and then turn off the mower. This will allow the oil to warm slightly and will remove more debris from the crankcase when draining.
Place an oil drain pan to the right side of the mower. Turn the oil fill cap counter-clockwise and remove the cap and dipstick from the fill tube.
Tilt the mower over onto its right side and drain the oil through the fill tube into the drain pan. When the oil completely drains, tilt the mower back onto all four wheels. Clean around the fill tube with a rag to remove any residual oil.
Slowly pour 20 ounces of SAE 30 motor oil into the fill tube. Place the dipstick and cap into the fill tube and twist the cap clockwise.
Turn the cap counter-clockwise to remove the dipstick from the fill tube and check the oil level on the dipstick. The oil level should be at the upper fill indicator. Place the dipstick back into the fill tube and twist the cap to secure it to the fill tube.