Water should flow from the thru-hull to the sea cock, to the sea strainer to the pump, to the heat exchanger (or engine if you don't have a heat exchanger). The hose from the seacock to the strainer should not be longer than necessary. If your plumbing looks like that, with all hoses connected, the pump covered, and the seacock closed, follow the steps below. If at any time water doesn't flow, you've located the problem.
1. Remove hose from the seacock. Open the seacock. Water should flow. Close seacock. Reconnect hose. 2. Remove hose from the strainer. Open the seacock. Water should flow. If not, lower the hose and see whether the water flows. Close seacock. Reconnect hose. 3. Loosen the cover of the sea strainer. Open the seacock. Water should fill the strainer. Close seacock. Reconnect hose. 4. Continue as above, one step at a time. I suspect you have air in the strainer that's preventing water from flowing. Alan Bergen 35 Mk III Thirsty Rose City YC Portland, OR On Thu, Jun 5, 2025 at 7:35 PM David Knecht via CnC-List < cnc-list@cnc-list.com> wrote: > As I always told my students, there are no bad questions or dumb questions > or insulting questions. Just questions. So I appreciate everyone trying > to help. It is why I love this community. Knowing you are all out there > gives me confidence to tackle problems that don't have YouTube videos to > walk me through. > > > To sum from some earlier questions: > 1. I verified that the pump shaft is turning. > 2. I am pretty sure the impeller is turning because the pump housing got > very hot very quickly from a brief test engine run with no water moving. > 3. I can find no obstructions to flow from the seacock to the pump. > > You comment actually makes me wonder if I have been working under some bad > assumptions in doing diagnostics. I had presumed that water would flow > rapidly into the raw water pump due to water pressure and the pump would > move it along. But as you pointed out, the pump is quite a bit higher than > the entry point, so maybe the pressure is fairly neutral there. If I open > the seacock, with the cover off the pump, should I see water flowing into > the pump? Does the pump simply move water that is already there due to > pressure flow, or does the pump actually draw the water into the > seacock/strainer by sucking it in? If the latter, then many of my tests > have been beside the point and nothing is blocking the flow of water into > the boat. It is more that the pump is not drawing the water in, which gets > back to the air leak issues mentioned. > > 1. If it is air leaks in the pump seal, I would propose to use a gasket > sealant line Form A Gasket in addition to the o ring to seal the cover? > Any reason that is a bad idea? > > 2. I asked earlier, but is there possibly a pump priming issue? I have > never heard of someone having to do anything to prime there raw water > pump. I did read an online engine thread where people had this problem > with a particular engine, but simply revving the engine got the pump primed > and pulling water. Dave > > David Knecht > S/V Aries > 1990 C&C 34+ > New London, CT > > > Your contributions help pay the fees associated with this list and help to > keep it active. Please help by making a small contribution using PayPal > at: > https://urldefense.com/v3/__https://www.paypal.com/paypalme/stumurray__;!!LIr3w8kk_Xxm!tg_8QDotKaqQd0wXsfIx6YjF-MW1iI-XRUNZo_pju74lXlsXEKfJptG3m2r12_1JMIX1bNQYK7ljZE4_hDq3YE4$ > All contributions are greatly appreciated.
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