Mercury Outboard Cooling Systems

Most newer Mercury Marine outboard engines use an enclosed cooling system. This means that there is a small tank on the top of the engine that uses a combination of fresh water and coolant.

This fresh water is circulated through the engine and through a heat exchanger. The fresh water, in this system, absorbs the heat of the engine. Mercury outboard motors are typically designed as open loop cooling systems. Meaning the motor draws water from the host body. That water is circulated through the engine, and fuel pump to maintain prop engine temperatures. After passing through the engine or fuel pump the water is then dumped back into the host body. Water is drawn into the water pump through the intake opening of the lower unit, where it passes through a cavity that ends up entering the pump itself. At that point, the impeller pressures the water into the long inlet tube leading to the bottom side of the powerhead. Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. For small or special-purpose engines, cooling using air from the atmosphere makes for a lightweight and relatively simple system. Cooling system, apparatus employed to keep the temperature of a structure or device from exceeding limits imposed by needs of safety and efficiency.

Water is inducted through the lower unit by a water pump impeller in the cooling system on an outboard and then forced upward to circulate throughout the powerhead, and eventually exits through the exhaust system.