how do you know how much oil to put in lawn mower?
Refill the crankcase with the amount and type of oil recommended by the engine manufacturer. Most small engines need 20 to 24 fluid ounces of oil. Small engines typically use SAE 30 single-weight detergent motor oil service-rated SG or higher, but some can use multiviscosity oils such as 10W-30 or 10W-40.