If you put too much oil in your lawn mower, it will likely start to blow white smoke as soon as you turn it on, unless the excess oil has been cleaned up thoroughly. This is because the excess oil will not be able to spread to an area of the engine where it’s used, and instead will coat the outside of the heated engine block and cause burning. While this is not the end of the world for a lawn mower, it’s important to not overfill the oil tank in your lawn mower, and to clean up any spills as soon as they happen to avoid the plumes of smoke that can result from burning oil.