Mercury Mariner 25HP 4-Stroke Outboard Service Manual 1997, Page 17Get this manual
Flushing The Cooling System Flush the internal water passages of the outboard with fresh water after each use in saltpolluted or muddy waterThis will help prevent buildup of deposits from clogging the internal water passages
Fuel System
Avoid serious injury or death from gasoline fire or explosionCarefully follow all fuel system service instructionsAlways stop the engine and 00 NOT smoke or allow open flames or sparks in the area while servicing any part of the fuel systemBefore servicing any part of the fuel system, stop engine and disconnect the batteryDrai the fuel system completelyUse an approved contai ner to collect and store fuelWipe up any spillage immediatelyMaterial used to contain spillage must be disposed of in an approved receptacleAny fuel system service must be performed in well ventilated areaInspect any completed service work for sign of fuel leakage
IMPORTANT: The engine must be run during flushing in order to open the thermostat and circulate water through the water passagesNOTE: You can have the outboard tilted or in the vertical operating position during flushing