The Yard Machine brand of lawn mowers, manufactured by MTD, require an engine oil for operation. This oil functions exactly like a car's oil, keeping the crankcase lubricated during operation. Without engine oil the crankcase and piston will overheat and seize up, and the engine will die. Always make sure the lawn mower has plenty of oil before each use.
The manufacturer recommends an SAE 10W 30 oil for the Yard Machine line of lawn mowers. This oil offers high quality performance in most general, all-temperature conditions and situations. However, when the air temperature drops below 40 degrees Fahrenheit, a thinner oil--such as an SAE 5W 30--may help engine performance. While this change isn't an absolute requirement it will help the engine run better and more efficiently in the colder weather.
Check the Oil
Before every use the operator should check the oil level. If the oil level in the crankcase falls too low, the engine can suffer damage very quickly. Unscrew the oil dipstick from its seat above the oil tank. Wipe the oil off the tip with a rag, then refit the dipstick completely into its place. Unscrew the dipstick again and check the oil level. If the reading on the dipstick falls below the "Add" line, you must add more oil before using the lawn mower.
Topping the Oil
Unscrew the cap on the oil filler hole and set the cap in a safe place. Set a funnel into the filler hole, which prevents any oil spills from starting a fire during operation. Add the oil slowly, about 1/8 to ¼ cup at a time, until the oil reaches the "Full" mark on the dipstick reading. Periodically check the oil reading when topping the oil off. Don't overfill the oil tank, which can actually damage the crankcase.
Changing the Oil
The oil inside the crankcase will go bad after 30 to 40 hours of operation. This oil must be drained and resupplied in the same manner as an automobile. However, the Yard Machine's oil changing methods vary from model to model. These methods also vary from a walk-behind to a riding lawn mower. Some mowers have an oil drain plug near the bottom of the oil sump, but others may not, and require tilting of the engine to drain the oil out of the oil filler hole. Take the mower to a professional if you don't feel qualified to change the oil yourself.