I have a 1975, 4.5 hp mercury outboard that runs great but won't seem to pump any cooling water. I have changed the entire water pump assembly including impeller, have flushed all of the water line segments with a water hose from top to bottom and in reverse, removed the powerhead from the drive shaft housing, cleaned all the cooling ports and replaced with a new gasket and have removed the pickup screen and checked for blockage...clean as well. The manual I have doesn't seem to indicate that this particular motor has a thermostat. Any suggestions would be appreciated!
