cooling water pumping problems

[orion]

Having intermittent raw water pumping problems with my 2006 SO 32i, any advise appreciated.

Shamefully I ran the engine with the Sea cock closed for over 30 minutes approx 3 weeks ago. The result was that the inlet hose to the salt water pump split. I was able to cut 2 inches off the hose and reconnect and everything was back to normal or so it appeared.

Since then on two occasions (on the return trip) the engine failed to pump water when restarted, not sure if it's a result of above or not.

The old impeller still looked ok and has since been replaced and all hoses checked. On the first occasion simply topping up the filter bowl with water seem to prime the pump and everything functioned correctly. On the second occasion topping up the filter bowl did not work, only taking the cover off the impeller pump (bowl still full) seemed to release an air lock and the pump primed and the water pumped.

I am noticing two things with the engine running and water pumping but not sure if normal or not.
(1) the water in the filter bowl only fills the bowl 20% of the height, should the bowl fill more, the stains on the filter suggest the water use to rise more?
(2) I am seeing air bubbles in the hose leaving the 'Vetus Exhaust Airvent' when I block the overflow hose with a finger the bubbles reduce. Could the airvent be sucking in air. Is this unit serviceable, took the top off to show a spring and seal.

Next step anyone??

[Zanshin]

Sealing the impeller assembly is quite important, an opening that is imperceptable to the eyes can be enough to keep the impeller from working correctly. Did you replace the gasket/seal when you changed the old impeller? How bad was the old impeller? Like this

or


If the latter, then perhaps you have some pieces of impeller in the water flow.

[orion]

Thanks for your help Zanshin

No gasket only rubber ring. Did not replace the ring only smeared with petroleum Jelly. The old impeller looked perfect, no bits missing or any obvious damage, one or two of the vanes did appear weak,

What are your thoughts on the filter bowl level & the air bubbles?

[sitara]

I have occasionally forgotten to turn on the engine water intake to! I note that True Design manufactures "monitored ball valves" and that the raw water intake valve can be connected into the engine start wiring so that the engine cannot be started with the valve closed.

Orion, the water level in the filter bowl sound normal or at least much the same as mine. I am surprised that failing to turn on the water would create enough suction to split the inlet hose! It sound like there is a blockage somewhere. I once had a fish block the inlet to the heads.

[sailbleu]

Right you are Sitara , this definitly sounds like a blockage between de filter and the inlet underneath the boat.
Or maybe even an airleak in that passage.
Disconnecting the filter , close the inlet valve and try to put some air pressure on , soaping the lot and afterwards open the valve and flush/blow it .
Or if possible , connect a waterhose and test and flush with water instead of air.

Regards

[Zanshin]

The bubbles tell me that air is getting into the circuit and the impeller doesn't prime well on air. I wonder if you could try using a small baggie or other plastic foil (perhaps Saran Wrap) and manually seal around the impeller assembly temporarily to see if the bubbles go away. If they do, then you probably have a bad seal. While blockage is still a possibility, this test is easy to do. Likewise test the hoses going into and out of the impeller for possible cracking, since I find myself pulling and bending those hoses when doing a change it might be possible that you did the same and it has come partially loose.

[rene460]

Like Sitara, I would be surprised if there was enough suction to flatten the inlet hose and presumably as a result, cause it to split.  However as the hose was split, I would suggest replacing all of it at earliest opportunity as it may be perished or weakened due to being bent until flat at some stage of its life.
My filter usually flows about 80% full of water.
I once had lack of water flow at the exhaust and suspected a blocked inlet.  I assumed possibly a plastic bag or a sea critter found a safe home.  I filled the filter with water with the valve closed then quickly opened it and not much happened, so possibly not the plastic bag.  I tried some vinegar to discourage sea life, worth a try as the next step was the slip way, and found that when I filled the filter again, the level dropped like a stone when I opened the valve.  I filled the filter a couple more times with fresh water and drained it by opening the valve.  No further troubles since, however sailbleu's ideas for more pressure would be less costly and worth trying before resorting to the slip if the inlet strainer on the hull still seems blocked.   Of course a helpful diver would also be useful.
But also consider blockage on the pump outlet (water exchanger inlet) as a cause for low water flow which may not sweep the remaining air through after you have opened the filter.   Do you have normal water discharge with the exhaust or is it pretty weak/infrequent?  If the flow is low after your priming procedure it may be worth removing the end of the heat exchanger and checking that the tubes are clear.
Rene460

[orion]

I believe the damage to the inlet hose to the impeller pump was caused by the large increase in heat and possible hot air from the heat exchanger rather than suction, or all three, the hose had got very soft and split at the hose clip.

With regard a possible blockage between the sea cock and the filter, the hose is transparent and I can see its clear right down to the sea cock. I can even see the sea water find its own level in the hose when i remove the filter cap. I will try and push something down through the sea cock to confirm its clear. You must remember the engine starts and water pumps no problem 90% of the time, it failed to re-pump twice after a sail.

What are your thoughts on this exhaust air-vent and the visible bubbles?

[rene460]

Hi Orion,

You are probably right about the effect of heat from the original incident damaging the hose.

Apart from the transparent hose which would be hard to block, there is a strainer below the inlet valve, outside the hull over the water inlet, usually a pressed metal affair with longitudinal slots to let the water in.  It stops large fish, but can catch a plastic bag.   You may be able to poke a wire down through the valve and stir it around.

i have not yet had reason to look closely at the exhaust air vent system and am not sure how it works.  I am watching your thread develop for when my turn comes, but I am sure that others will answer that one.

Rene460