1995 Mariner Mercury Outboards Service Manual 50HP 4-Stroke, Page 17Get this manual
Out-of-Season Outboard Storage As safety precaution, when boat is in storage, remove positive (+) battery cableThis will eliminate possibility of accidental starting of engine and resultant overheating and damage to engine from lack of waterIn preparing an outboard for out-of-season storage, precautions must be considered: 1) The engine must be protected from physical damage and 2) the engine must be protected from rust, corrosion and dirtFUEL SYSTEM
IMPORTANT: Gasoline containing alcohol (ethanol or methanol) can cause formation of acid during storage and can damage the fuel systemIf the gasoline being use contains alcohol, it is advisable to drain as much of the remaining gasoline as possible from the fuel tank, remote fuel line, and engine fuel system
PROTECTING INTERNAL ENGINE COMPONENTS 78Remove the spark plugs and inject small amount of engine oil inside of each cylinderRotate the flywheel manually several times to distribute the oil in the cylindersReinstall spark plugs