The water-cooled version with the smooth water cooling cylinder and smooth cylinder head. 4-Gears and 280-73 Liste 5 engine block. From the well-known advertising leaflet with the lying lady on the orange KS. One of the most wanted Zündapp mopeds. Many models were later converted by their owners from air to water cooling. The water in the cylinder casing is heated by the running engine and is automatically transported upwards. Hot water expands and rises upwards. Via the mounted radiator, which hung between the vertical frame tubes, the water cooled again and was brought back into the cooling jacket through the water hoses. Everything without a water pump according to the thermosiphon cooling principle. The water jacket makes the 517-36 quieter than an air-cooled Zündapp moped.