Cars do not come with oil catch cans because it is not a necessary part of the car's operation and function. An oil catch can is an aftermarket accessory that helps to minimize engine sludge build-up by collecting excess crankcase emissions from the PCV system. This device, typically installed between the valve cover and intake manifold, captures any residual oil vapor in order to prevent clogging up the entire air intake system, as well as preventing oily residue from building up on vital components such as spark plugs and oxygen sensors. Although these types of devices are beneficial for those looking for extra protection against buildup within their engines, they are still considered optional extras rather than being a regular feature when one purchases a new car.