OMC Stern Drives And Motors 1964-1986 Repair Manual., Page 338Get this manual
COOLING 9- DESCRIPTION
An impeller-type pump (make-up pump) installed in the vertical drive supplies circulating coolant the engineIn addition this pump, conventional centrifugal-type recirculating pump is mounted the of the engine cylinder blockThis circulating pump similar the pump installed on an automobile engineBecause of the pump installed the stern drive, the following caution MUST ALWAYS observed before starting the engine for any reason, at any time: CAUTION: Water must circulate through the lower unit to the engine any time the engine is run to prevent damage to the water pump in the lower unitJust five seconds without water will damage the water pumpThe impeller pump the vertical drive is keyed the vertical driveshaf and is self-priming pumpDuring slow-speed operation, the impeller functions centrifugal pumpAn eccentric action is developed by the impeller because is offset from center the housing