Q. What is the difference between air cooled and oil cooled engine?

In the process of chemical energy into mechanical energy by burning fuel and air, the engine tends to get heated and thus requires cooling in order to perform smoothly. An air-cooled engine is designed with fins on the outside which increase the surface area of the motor, thus improving airflow around it. In essence, these fins create channels around the engine and use passing air as a natural coolant which helps dissipate heat generated from the cylinder. Now, in case of oil-cooling, the circulating oil is cooled by pumping it through a radiator-like cooler which uses air flowing through it to cool down the engine oil. The cooled oil is then sent back to the engine and the process repeats itself to maintain its operating temperature and viscosity. While a mid-to-high-power air-cooled engine does benefit from oil cooling, since the oil is not directly used to cool engine parts directly, it doesn’t really qualify as a cooling system per se - even if manufacturers like to say otherwise.

Not to worry, all are good until that engine don't get heated up

Difference is negligible