How does the cooling system work on an outboard?

If you’re a boat owner, you probably know that the cooling system is one of the most important parts of your outboard motor. It’s responsible for keeping the engine from overheating and ultimately seizing up. Here, we’ll go into more detail about how the cooling system works on an outboard, so you can better understand how to maintain it and keep your boat running smoothly.

First, it’s important to understand that there are two types of cooling systems used in outboards: the raw water system and the closed-loop system. The raw water system, as the name suggests, pumps in water from the body of water your boat is in (such as a lake, river, or ocean) to cool the engine. The closed-loop system, on the other hand, uses a separate coolant (usually a mix of water and antifreeze) that circulates through the engine to absorb heat, then passes through a heat exchanger, which cools it down before it goes back into the engine.

Raw water systems are more common and simpler than closed-loop systems, so let’s focus on how they work. When you start your outboard, the impeller (a small, rubber fan inside the water pump housing) begins to spin, which draws water in through a series of intake grates at the bottom of the lower unit. The water travels up through a tube and into the engine where it circulates through the coolant passages to absorb heat from the engine block and cylinder head. The water is then expelled through the exhaust system and back into the body of water.

One common problem with raw water systems is blockages in the intake grates. These can be caused by debris (such as seaweed or trash) getting caught in the grates, or by growths of barnacles or other aquatic life on the lower unit. If the intake grates become blocked, water flow to the engine can be reduced or cut off entirely, which can cause the engine to overheat. That’s why it’s important to check and clean the intake grates regularly to keep water flowing freely.

Another maintenance task you should perform regularly is flushing your outboard after each use in saltwater. Salt can leave behind corrosive residue in the cooling system, which can cause damage over time if not removed. To do this, connect a water hose to the flush port on the lower unit and turn on the water. Then, start the engine and let it run for several minutes to flush out any salt water.

In summary, the cooling system on an outboard is critical to the engine’s function, and it’s important to understand how it works and how to maintain it. Regular cleaning of the intake grates and flushing the system after saltwater use will help extend the life of your outboard and keep your boat running smoothly.

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