Q. What is air and oil cooled system and how it is different from liquid cooling system?

Primarily there are 2 types of cooling used for the engine. Air and Liquid. Air cooled engines are cheaper but the cooling may not be uniform since the rear portion of the cylinders cannot be cooled by air when the vehicle is moving forward. Liquid cooled engines are more expensive to make due to the cooling jackets that go around all the heat generating parts of the engine. Liquid cooled engines have more uniform cooling and they must have a radiator. Either of these can have a supplementary oil cooler, which has a small radiator that takes away the heat from the oil that circulates inside the engine. Oil cooling is not an alternate to either air or liquid cooling, but only supplementary to those. Hope this helps.

Oil Cooled and Water Cooled are terms used by Manufacturer's to differentiate the slight difference between the cooling systems. Oil cooling: Technically , An oil cooled engine is predominantly air cooled with oil cooling assistance, the majority of the heat transfer is through the fins on the cylinder block.Air-cooled engines are fuel efficient, affordable and require lesser engine space than that of liquid cooled engines. The Maintenance costs of liquid cooled ones are higher than air-cooled engines. Liquid cooled ones are easy to operate (better riding experience) but certainty of liquid spilling out is high.

In layman terms, air cooled means there is no special cooling mechanism and the air outside will be used to cool the bike. Oil cooling and liquid cooling is as described above. In short liquid cooling>oil cooling>air cooling. Also the same for maintaince cost.