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Cooling systems
There are two types of cooling system on the marine engine.
Raw-water system The body of water you are floating in, be it sea or fresh water, is pumped around the outside of the internal parts of the engine in what are called cooling galleries by a raw-water pump, also called an impeller pump. There needs to be a constant flow of water around the system not just to keep the engine at its operating temperature but also to lubricate and cool the working parts such as the rubber impeller and exhaust system. Raw water goes to the pump and then splits, one feed going to the
cooling galleries and the other to the exhaust. Once the water exits the cooling galleries, it will join the feed to the exhaust and both are pumped out of the boat via the exhaust pipe outlet. There is a thermostat on the engine side to keep the raw water in the cooling galleries at a constant temperature round the engine. When it closes, all the raw water will circulate within the cooling galleries until it reopens, enabling cooler water to enter. This process can repeat quickly or slowly depending on engine load and speed but the end goal is for the temperature to stay as constant as possible within the engine. We will explain this further, later in the chapter.
Raw water flow
Engine cooling galleries Sea-water filter
Exhaust Sea-water pump
Hull valve
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Stress-free engine maintenance
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