the air cooled one is a duitz air diesel . they are very reliable about the only maintenance it will ever need is filters and the cooling fins cleaned from time to time. it is lighter than a water cooled version and freezing will not hurt it.
Water cooled is hydrolic obviously and it don't really go faster depends what horse power the engine or motor is. Air cooled is just your basic diesal that need a spark to start and needs air to cool down.
In water cooled Diesel Generators.The diesel enginee is cooled by water and in Air cooled diesel generators enginee is cooled by air.In water cooled, water is circulated around diesel enginee the heated water is cooled by radiator.And in air cooled Pistonblock is in direct contact with air pistonblock has fin or groves to increase surface area for better heat exchange.
probably only that the water cooled one has a higher efficiency. because of higher temperature gradient. can't say anything for sure.
