Join Date: Dec 2004
Location: Alameda, San Francisco Bay
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The vast, vast majority of sailboats have a two loop cooling system. The primary loop circulates water/coolant through the engine block and is moved by the metal water pump mounted on the front of the engine block. This water/coolant circulates on the primary side of the heat exchanger (think car’s radiator). The secondary loop takes water from the outside of the boat and flows it through the heat exchanger. This water is moved by the bolted on water pump that you replaced the rubber impeller on. The engine’s zinc is mounted in the “outside water” side of the exchanger. If you have a heat exchanger, you have a zinc. Look for a brass bolt head mounted on the bottom side of exchanger where the sea (outside the boat) water comes in. Chances are when you remove the brass bolt head, you won’t see a zinc as it has completely dissolved some time ago. What is your engine's operating temperature? It should be around 160 – 165 degrees, 180 max. If it is over this this, you need to take out your exchanger and clean it out (you can go to a radiator shop for this). If you are around 180, you should still clean it, but it is not yet mission critical.
For those of you that don’t have a heat exchanger, you still have a zinc mounted somewhere. Consult your engine’s manual. Getting a heat exchanger re-cored is easy, re-coring an engine block is hard. That’s why most boats have heat exchangers.
Last edited by GeorgeB; 02-24-2010 at 04:11 PM.