Re: merc 4.3 coolant pump question
You should really take the time to understand the cooling system on your boat. IMHO cooling system failures (including lack of maintenance on the elbows / risers / manifolds) are probably the #1 reason why engines come out on boats. The thing is you can follow other poeple's advice or a maintenance schedule ... but if you understand how everything works you'll KNOW what needs to be done and when ... you will KNOW when something is a problem.
To answer your question directly, there are two water pumps on your boat. One that circulates coolant around the engine (I take it you have a closed cooling system). This water pump has a cast iron impeller and circulates the coolant by flinging it off to the side at high speeds. It is located at the front of the engine. The other water pump is located inside the lower leg. It is inside a stainless steel housing and has hard rubber blades. Its purpose is to pump sea water to your heat exchanger which cools the engine coolant which then in turn cools the engine. This raw water pump as iti s called also pumps into both of your exhaust manifolds and risers. Therefore it cools the exhaust manifolds, exhuast gasses and helps to muffle the noise. So as you can see, its very important.
This raw water pump is different because this style of pump can actually generate some suction force to pull the water in. Whereas the coolant pump isn't designed to do that.
