A raw water cooled engine has one water pump. It pulls in water from outside of the boat, circulates it through the engine block, and out the exhaust.
A fresh water cooled engine has two pumps. One, like the water pump in your car, circulates a mixture of fresh water and antifreeze through the engine block and the fresh water side of the heat exchanger. The other pump, generally the one with the rubber impeller, draws in water from outside the boat and supplies it to the heat exchanger (to cool the fresh water in the engine) and out the exhaust. The heat exchanger performs the same function as the radiator in your car. I used to run a 1987 Hunter 37 as a charter boat for boy scout sail training programs. It had a 3GM30 with a SenDur fresh water conversion kit on it. The other Hunter we used had a 3GM30F, which was fresh water cooled from the factory. I seem to recall that Yanmar stopped building raw water cooled marine engines sometime in the 90s. Rick Brass Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Mazen Aziz via CnC-List Sent: Sunday, August 2, 2020 10:36 PM To: cnc-list@cnc-list.com Cc: Mazen Aziz <mazen.a...@olympian.org> Subject: Stus-List Water pump Hello everyone, Hope you had a great weekend. I was in the process of changing the impeller and I think I have two water pumps? I’m looking all over the manual and that top water pump(picture attached) doesn’t exist in the manual. My engine is 3gm. Anyone familiar or has similar? What’s the purpose of two water pumps? Thank you all, Enterprise 35-3 San Francisco MAZEN AZIZ https://mazenaziz.wixsite.com/mazenaziz “To most people, the sky is the limit. To those who love aviation, the sky is home. “Jerry Crawford "I don't think that architecture is only about shelter, is only about a very simple enclosure. It should be able to excite you, to calm you, to make you think." Zaha Hadid "It isn't the mountains ahead to climb that wear you out; it's the pebble in your shoe." Muhammad Ali
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