A cooling system for an outboard motor having a water propulsion device and an internal combustion engine positioned in a cowling, the engine having an output shaft arranged to drive the water propulsion device, is disclosed. The cooling system includes a coolant delivery mechanism driven by the engine, the delivery mechanism arranged to deliver coolant selectively to at least one of two coolant jackets of the engine. One coolant jacket is associated with at least one combustion chamber of the engine. The other cooling jacket is associated with an exhaust manifold for that combustion chamber. The cooling system also includes at least one coolant drain line through which coolant may drain from each of the cooling jackets of the engine.