Is it correct to say that a Yanmar 2GMF is a "fresh water" cooled engine, meaning no heat exchanger but rather the lake water passes through the block? Only 1 zinc required?
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Engine Cooling
- Thread starter gr8_2_av8
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Fresh water cooled means there is an engine cooling system separate from the raw water plumbing which cools the engine system via the heat exchanger. A raw water cooled engine has no separation and therefore no heat exchanger. You'd need to consult your engine manual or another 2GMF owner to verify whether there is/are zincs but I don't think so. As an fyi, raw water cooled engines can have anodes.
Gr8-2
Don't confuse the fact that you sail on fresh water with 'fresh water cooling' (FWC). If you have no heat exchanger (HX) then the lake water is what cools your engine via a 'raw water cooling' (RWC) jacket - your raw water just happens to be fresh water.
To make things even more confusing with a 'fresh water cooled' engine there is a closed circuit of anti-freeze (not fresh water) that takes heat from the engine to the HX where the raw water takes the heat out of the boat. A more accurate description of FWC would be cooled by anti-freeze.
Raw water (fresh or salt) simply circulates through the engine in a RWC scenario.
Don't confuse the fact that you sail on fresh water with 'fresh water cooling' (FWC). If you have no heat exchanger (HX) then the lake water is what cools your engine via a 'raw water cooling' (RWC) jacket - your raw water just happens to be fresh water.
To make things even more confusing with a 'fresh water cooled' engine there is a closed circuit of anti-freeze (not fresh water) that takes heat from the engine to the HX where the raw water takes the heat out of the boat. A more accurate description of FWC would be cooled by anti-freeze.
Raw water (fresh or salt) simply circulates through the engine in a RWC scenario.
The GMF designation means a "fresh water cooled" GM model. As others have said, there is coolant in the closed system engine block that re-circulates through a heat exchanger .. just as in most automobiles.. The radiator in a car is the heat exchanger where the coolant rejects heat to the air passing through.. In the little Yanmar, the heat exchanger rejects heat to the "raw" water that is passing through. The raw water side is a once thru system .. The elastomer impeller pump pulls in the raw water from outside the boat and pumps it thriough the heat exchanger where it picks up heat from the "fresh" coolant water in the block. It does not mix with that block system, just as the coolant in your car does not (normally) mix with the air flowing through the radiator. The raw water (seawater or lake water) then leaves the heat exchanger and gets mixed into the exhaust gas stream in the elbow which cools and quietens the exhaust. It goes overboard then and is what you hear splashing from the exhaust exit.
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