a rad, water pump , water hoses
Just as you said, in air cooled, air is passed over the engine usually by a fan. In a water cooled engine water is piped through the engine. In boats there can be raw water cooled or an enclosed system that recycles the water, cooled by a fan. In the raw water the water is drawn in goes through the engine and is mixed with the exhaust and pumped out the stern. Diesel generators generally have a radiator system. There are dual systems that have both.
An air cooled engine's temperature is maintained by a flow of air over the engine itself (usually with an assortment of cooling fins molded into the design of the block and head(s)) to reduce the heat produced by the engine. A liquid cooled engine circulates a liquid around the engine (in a water jacket) and passes that liquid through a radiator or heat exchanger in the case of a marine application to dissipate the excess heat.
