If you're new to the idea of doing this work yourself, you'll want to avoid common mistakes people make when changing lawn mower oil and vehicle oil. One mistake is adding oil made for automobiles to your lawn mower. Because the car's motor is water-cooled to regulate its temperature, though, its oil isn't intended to endure high engine temperatures. To achieve better performance in these temperatures, lawn mower oil uses different formulations than what's used in a motor vehicle. Consequently, you don't want to put car oil in your lawn mower or vice versa.