Forced Air Cooling: A fan makes a difference between natural air cooling and forced air-cooling. The fan supplies the required air to carry away heat from the engine cylinder. As indicated by the name of cooling system, the air is forced towards the engine cylinder by the fan that passes over the engine and takes away heat and discharges to the atmosphere. Generally, this type of cooling is used in scooters. In bigger size engines, forced air cooling mechanism or liquid cooling (water or other coolants) system may be required.