Your Toro walk-behind mower may have a Tecumseh or a Briggs & Stratton engine, but the procedure for changing the oil is similar for both. Change the oil after the first two to five operating hours, then at least once a year or every 25 operating hours afterwards. Most Toro walk-behind mowers take 20 oz. of SAE 30 detergent oil classed SF, SG, SH, SJ, SL or higher, but check your owner's manual or ask when you purchase the oil for the type of oil specified for your particular mower.
Run the mower for five minutes to warm the oil so it will drain more easily.
Disconnect the wire from the spark plug by pulling the rubber cap off.
Unscrew the black cap of the dipstick, located on the top of the mower, and pull the dipstick out.
Place a pan beside the mower, on the side near the dipstick hole, to catch the used oil. Tip the mower sideways so the dipstick hole is on the lower side and let the oil drain into the pan. When the oil no longer flows out, set the mower upright again.
Pour about 15 oz. of oil into the dipstick hole. Wipe off the dipstick with a rag, wait a minute for the oil to settle, insert the dipstick, pull it out and check the level. Gradually add more oil and check again until it reaches the "full" mark on the dipstick but no higher. If you accidentally overfill, tip the mower again to drain out the excess oil.
Insert the dipstick into the hole again and turn the cap clockwise to tighten it. Take the used oil to a recycling center for disposal.