Water Lift Flow Problem

[model 10]

After some rough sailing there is no water flow through the exhaust when you start the engine. I remove the outlet hose from the heat exchanger and get some flow, re-connect the hose and all is well. I have checked the hoses and the vented loop and all is well. The engine temp is fine when water is flowing. The amount of water coming from the exhaust seems normal when the system is working. The salt water pump has a new impeller and cam.
This problem is new this for this cruise.

[FlyingCloud1937]

VARMETS

Originally Posted by Guy

After some rough sailing there is no water flow through the exhaust when you start the engine. I remove the outlet hose from the heat exchanger and get some flow, re-connect the hose and all is well. I have checked the hoses and the vented loop and all is well. The engine temp is fine when water is flowing. The amount of water coming from the exhaust seems normal when the system is working. The salt water pump has a new impeller and cam.
This problem is new this for this cruise.

[GILow]

Originally Posted by Guy

After some rough sailing there is no water flow through the exhaust when you start the engine. I remove the outlet hose from the heat exchanger and get some flow, re-connect the hose and all is well. I have checked the hoses and the vented loop and all is well. The engine temp is fine when water is flowing. The amount of water coming from the exhaust seems normal when the system is working. The salt water pump has a new impeller and cam.
This problem is new this for this cruise.

This is odd. I just read about something similar with the Sydney Hobart in 1998. In the interview they reckoned the engine overheated as the pickup point was sucking air from time to time during the big waves.

When I read that I thought it was highly improbable, I would have thought the raw water pump would have self primed again practically instantly, but could this be the case for you? When you say "rough sailing" is it possible the boat is healing over enough to suck air in to the pickup and if so, does this stop the water flow until you effectively bleed it again by removing the outlet hose and thus removing a bit of the head or some minor back pressure?


Matt

[Ziggy]

Put some vaseline or silicone grease on the impeller and see if that helps. Raw water pumps can definitely loose prime (personal experience).

[Neo]

Hmm. I learn something new every day. Never would have thought that could happen.

[Vasco]

Loss of prime. Check the strainer next time to see if it's full.

[model 10]

Those are all good points. As I think back on this, the strainer has been empty during these episodes. If I crack the bowl it fills immediately but I'm not sure the system starts pumping right away until remove a hose downstream. My thinking was if the strainer can get water that was not the problem but maybe the pump is loosing prime and if I just waited a moment the system would have started pumping.
Could this be caused by a leaking gasket in the strainer? There is no sign of any water leak but perhaps air could be getting in?
I'm not sure the boat was rolling enough to uncover the inlet as it is pretty far down, but maybe.

[Jim Cate]

Had similar symptoms some years ago, and the culprit for us turned out to be a worn cover plate on the vane pump. Reversing the cover (at least on that particular Johnson pump) gave a fresh surface, and the symptoms disappeared.

Just another thing to check...

Good luck

Jim