The John Deere 318 was manufacture from 1983 to 1993; it featured an 18-horsepower Onan gasoline engine. Changing the oil is general maintenance that you must complete every 100 hours of operation. If left unchanged, the oil will start to break down and no longer provide the lubrication needed to keep the internal parts cool, causing damage to the engine.
Park the lawn mower on a hard, level surface. Set the parking brake and remove the key from the ignition.
Raise the hood covering the engine; on the right side of the engine is a shroud cover. Remove the three screws holding the shroud in place with the 3/8-inch wrench; this will expose the oil filter and oil plug.
Place the oil pan under the oil plug to catch the draining oil. Remove the oil drain plug at the bottom of the engine, in front of the oil filter, with the crescent wrench; allow the oil to drain completely. Turn the oil filter counterclockwise to remove it.
Install the new oil filter; turn until it's hand tight. Reinstall the oil plug with the crescent wrench. Remove the oil dipstick located on the left side of the engine. Insert the funnel into the dipstick hole; pour 1 1/2 qt. of oil in. Check the oil with the dipstick. Keep adding oil until the mark on the dipstick indicates it's full.