A Craftsman lawnmower with a 4.5-horsepower engine requires a sufficient amount of lubrication to keep the piston from locking up inside the cylinder. Too much oil in the crankcase can also damage the oil pump and the valves around the crankcase. For this reason, make sure you supply your Craftsman lawnmower with the right amount of engine oil.
The Craftsman lawnmower doesn't come supplied with oil already in the tank. You must fill the oil tank before beginning to use the lawnmower. The first time filling the tank will require only 18 fl. oz. of engine oil, due to the residual oil left over from the manufacturer's quality testing procedures at the factory. However, the capacity of the oil tank on a 4.5-hp Craftsman lawnmower engine is 20 fl. oz. So, for regular oil changes, fill the tank with 20 fl. oz. and not 18 fl. oz.
Type of Oil
Briggs and Stratton manufactures the engine used in a 4.5 Craftsman lawnmower. The manufacturer recommends using an SAE 30 oil in all conditions above 32 degrees Fahrenheit. If you're operating the lawnmower in temperatures below 32 degrees Fahrenheit, the manufacturer recommends using an SAE 5W 30 oil in the engine. Using these oils will provide adequate protection as long as there is a sufficient supply of oil during operation. Never use reclaimed automotive oil or any other oil that has been previously used.
Checking the Oil
Before every use, you'll need to check the supply of oil to ensure adequate protection. If the oil tank doesn't have enough oil, the engine will seize. Make sure the lawnmower is on a flat surface before you check the oil reading. Pull the oil dipstick from the oil spout, wipe off the tip with a rag and reinsert the dipstick. Pull the dipstick out again and check the reading. If the oil line is below the "Full" section, add at least 5 to 10 oz. of oil slowly through the oil filler hole.
Changing the Oil
Craftsman recommends changing the oil in the 4.5 lawnmower after every 25 hours of operation. Position the lawnmower on a flat surface, and disconnect the spark plug wire from the end of the spark plug. Remove the oil drain plug from the bottom of the unit and let the oil drain into a pan. When the oil has completely drained from the engine, refit the plug into the unit and fill the oil tank with 20 fl. oz. of SAE 30 oil. Don't overfill the oil tank, or it will start smoking near the muffler.