Can you use SAE5W20 for 4 cycle lawnmower?

most small engine manufacturers recommend a single viscosity oil...usually SAE30. Some even recommend that it be non detergent oil. Whatever the owner's manual recommends is alwaysthe first and best choice. If you have no other choice for some reason, you can use the 5W20, but check the oil before each and every time you use the mower - it will go through the oil rapidly. If that sounds like a bother - that's why you use the oil recommended in the owner's manual.