Air-cooling systems work by forcing air to the metal fins around the engine cylinder. Liquid-cooling systems, on the other hand, have a radiator and a water pump. The pump distributes the liquid coolant to the engine block through hoses, and the heat from the engine is transferred to the coolant. The heated liquid then goes to the radiator where the air cools it. Modern generator engines commonly use liquid-cooling, but you will find most smaller portable generators are air-cooled models only.
Air-cooled engines are generally cheaper to produce than liquid-cooled engines. This is due to fewer parts and can function without any radiator. Air-cooled engines do not need any coolant. Their chances of overheating are minimal. Air-cooled engines can easily overheat.
Since air-cooled engines have the potential to over-heat, using them full time is not recommended. Air-cooled engines that fail generally require a major overhaul and their maintenance and repair tasks tend to be more frequent and more time consuming. Because air-cooled engines in portable generators work at much faster speeds, they also ware out much faster. Oil break down also happens faster and damage can occur with little warning. Aurora Generators recommends you do not run air-cooled engines full-time. Shut down your air-cooled engine every few hours so it can cool. This is a good time to check your oil, add fuel and perform a general maintenance and/or inspections.