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Old 16-06-2013, 18:11   #1
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Thru Hull size intake on volvo md11c

Hi there. Im hauling my boat out this summer and Im going to scrap the old gate valves and replace the raw water one with a seacock. Currently there is a two and a half inch gate valve for the water intake witch used to be coupled with the sink drain in the galley. there is a T on this valve that reduces it to a half an inch. Im new to diesel engines and this to me seems a very small hose to be cooling the engine. But since it is original and the water pump">raw water pump only takes a fitting that size I guess its ok. And it works. My question is if it matters to have the thru hull bigger than a half inch when the hose is only that size??? Im going to need to drill out a new hole for the smaller thru hull, but I like the idea better than buying a 400$$$ bronze seacock that is 2 and a half inches. If anyone can help me out with this let me know.
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Old 16-06-2013, 18:36   #2
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Re: Thru Hull size intake on volvo md11c

Hi Liveitwell, as far as I know it is better to have a dedicated intake for the engine. By combining the intake for the engine and the sink drain you will suck almost everything you put true the sink into the cooling system of the engine. Apart from food parts also all soap you use in the sink will go in the cooling system, I have no idea if this can harm the impellor or other parts but it doesn't sound good.
To answer your question; a dedicated raw water intake can have the same size as the hose, increasing the intake size will not give any advantage because of the hose size.
My volvo penta md2020 has a 3/4 raw water intake.
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Old 17-06-2013, 04:55   #3
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Re: Thru Hull size intake on volvo md11c

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Originally Posted by Bregts View Post
Hi Liveitwell, as far as I know it is better to have a dedicated intake for the engine. By combining the intake for the engine and the sink drain you will suck almost everything you put true the sink into the cooling system of the engine. Apart from food parts also all soap you use in the sink will go in the cooling system, I have no idea if this can harm the impellor or other parts but it doesn't sound good.
I'll start at the end, one common "lubricant" used when rebuilding raw water (Jabsco type) pumps is dishwashing liquid (a.k.a. soap). The idea being to lubricate the rubber vanes until the water takes over that duty.

As such, "soap" won't be a problem. Neither will small particles (e.g. what's left over after the "garburator" has done its thing). They will just flush through the system. Not unlike other debris that's not caught in the raw water strainer. You do have one of those right?

Having said that, I would hesitate connecting a sink drain to the suction side of the raw water system. My concern would be sucking air instead of water. The inherent risk of yet another through-hull is offset by that concern.
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