There are two types of cooling systems found on MerCruiser engines, raw water and closed loop. Raw water cooling systems use the body of water in which the boat is operating to cool the engine. Closed loop cooling systems have a freshwatercoolant that circulates through the engine block and cylinder heads before being cooled by a heat exchanger.
The main component of either type of cooling system is the sea water pump. The raw water pump pulls in seawater from outside the boat and pushes it through the engine to absorb heat. The fresh water pump does not come into contact with seawater; instead it only circulates the glycol-based coolant mixture through the engine block, cylinder heads, and hoses. A belt connects the sea water pump pulley to the crankshaft pulley; as the crankshaft turns, so does the impeller inside
the raw water pump.
As seawater enters the raw water side of things, it first passes through a strainer (often called a “pick-up”) which removes any large debris that could potentially damage or clog up your impeller. From there, it goes straight to your sea water pump where it’s then pushed through your engine block via hoses connected to waterways inside your engine casting (the big aluminum housing that contains all your internal engine parts). As it flows through these waterways, heat from inside your engine is transferred to
the cooler seawater passing by on its way out. These waterways are located around areas that create most of the heat in your engine such as cylinders, exhaust valves & manifolds, and bearings supporting moving parts like connecting rods and camshafts..
Once cooled seawater exits your engine back into open waters, there’s one more stop before it can be considered “job done” – The Raw Water Cooling System Heat Exchanger. Your MerCruiser’s Heat Exchanger works similar to how radiator works in a car except instead of air flowing across metal fins filled with hot coolant liquid, raw seawater does this job as it flows past tubes carrying hot glycol mix coming from youengine before finally being discharged overboard via an exit hose..
Closed Loop Cooling Systems work similarly but instead of using raw seawater for cooling purposes; they recirculate a 50/50 mixture of fresh drinking quality distilled H2O & propylene glycol anti