strainer empties when heeled?

[hornby sailor]

water strainer empties when heeled, sailing, doesn't fill back up when i start the motor, unless i open the lid, then it fills. Yanmar 3gmd raw water cooled. third time now, whats up with this? first time I didn't let on, (short hop back to dock)second time, sailed right to the dock, she thought i was a pro. Third time i checked the strainer, don't know if I'll get a fourth date. come on sailors, I really need you here.

[LittleWing77]

If it's on one heel versus the other, your thru-hull is in the wrong place.

Have you had a look at the raw water inlet to see if it's blocked? Other than that, maybe syphoning/air lock...?

I'm just brainstorming, though. We need Wotname, Compass790 and/or tkeithlu to weigh in here.

Fair winds,
LittleWing77

[Tomodore]

Agree with above, is inlet to sea strainer near keel and not too far aft so it's never out of the water? Might check your impeller by now since they don't do well running dry.

[hornby sailor]

was fine for seven years, fills rapidly when cap is off. now going to look at impellor, see if its worn and letting air break siphon? not sure of dynamics of that though.

[tkeithlu]

It doesn't all add up in my mind, but you didn't move the inlet or start sailing at a 70 degree heel, so I'm ready to explore other problems than the inlet being in the wrong place. It used to work. Now it doesn't. Something changed, but it is not the location of the inlet.

The air is between the inlet and the pump. That whole area is at a vacuum when the pump is working. While I can't quite see how the pump sucking air somewhere matches with it's fooding when you open the lid, I would start by carefully checking that whole circuit for a leak inward. Include the lid itself. Look for a loose hose clamp, for example.

Second, I would check the inlet for a partial blockage. If the pump is trying to suck more water than is readily available, the vacuum increases. The tendency to leak inward goes up. The reflill that you observe when you open the lid may not be fast enough to meet the demand from the pump.

Try a test at the dock. See if you can replicate the failure with the boat sitting level. You know that the inlet is under water then. When you start the engine, if you get a glob of water followed by none, you've recreated the failure, and it's gotta be air sneaking in between the inlet and the pump.

This is an interesting "who done it". Do come back with a progress report as you chase down the problem.

[tkeithlu]

If none of that works, I'd start looking at the "breaks siphon" scenario. For this one, the pump will need to be above the waterline, and the whole system drain backwards through the heat exchanger and then through the pump. That would mean an impeller that leaked badly. Where it doesn't make sense is flooding when you open the lid. In this scenario, the water in the system should be sitting at the waterline, and not move when you open the lid.

[GreenWave]

Have you considered that your thru hull may be blocked or partially plugged?

[LittleWing77]

Originally Posted by tkeithlu

It doesn't all add up in my mind, but you didn't move the inlet or start sailing at a 70 degree heel, so I'm ready to explore other problems than the inlet being in the wrong place. It used to work. Now it doesn't. Something changed, but it is not the location of the inlet.
. . .

This is an interesting "who done it".

Do come back with a progress report as you chase down the problem.

See?
I KNEW you would offer a voice of reason!

Now where the heck are Wottie and Compass790...?

Cheers,
LittleWing77

[BillKny]

My bet is the problem is with the raw water pump, not anything to do with the plumbing.

It is perfectly normal to have air bubbles travel under the hull when sailing fast or in waves. They travel back and when they get to the thru-hull, up they go and collect in the strainer. You just never noticed before. Now that your raw water pump has worn out it can not self-prime.

Fix pump, fix problem.

[Cadence]

If your impeller is shot is it the cause or the result? If changing it does not solve the problem I would look at the pluming for a minor air leak which you would never notice under normal circumstances. You are going to have a certain venturi effect at your through hull while sailing.

[sailor_ed]

The OP said RAW water cooled engine. This may well be pertinent. No?

Ed

[hornby sailor]

it didnt happen while just motoring out, and didnt happen on a gentle sail, just on 3 days of 15* heeling. mixing elbow, exhaust manifold, pump, and thermostat all removed and put back in, in the interim, thinking of a blockage somewhere. will put new impellor in , after check connections on way to strainer. and check flow rate changes upon startup,

[rondelais]

Also check the water pump cover for wear. If it is worn by passage of time and water, the seal to the impeller is poor, allowing a lot of leakage. You can reverse the cover, or file it flat again, or just replace.

[Wotname]

Lot of good information already posted so excuse me if I recap some of it without crediting previous posters.

We know the cooling system used to work but is now intermittent presumably occurring only after significant time heeling.

Was the engine running during this heeling period???

My take - the pump has slowly worn over the past seven years the OP has owned it and may have never been rebuilt in it's life (likely to 20+ years). It has lost it's ability to 'suck' enough. It used to have enough but now it doesn't have enough. As BillKny says 'Fix pump, fix problem'.

Check rear of pump chamber face for wear or scoring, if fitted, replace rear wear plate. Replace cam lobe, replace front cover, use the correct thickness front gasket or O ring as required, replace impeller, replace all seals and bearings.

You might be surprised how much water the pump will deliver after a full rebuild.