Water intake problem

[Daydream believer]

Engine is a Volvo Penta 2020 MD Sail drive
Never had a problem with water cooling on sea water side in 13 years from new until August when I had a lift out for mid season pressure wash.
When I started engine no water came out & i had to prime the system at the filter. I guessed perhaps some dirt had been pushed into the slots in the saildrive.
Everything worked OK & I motored out of Burnham yacht harbour & sailed to the Swin.
Due to shallow water I decided to start the engine in case I ran aground & no water came out. I checked impeller & had to change as running dry for a few minutes lost a vane.
Still no water in spite of pouring water in to the filter with a kettle.
Finally got water in by laying boat over ( 25Kts wind) on inlet side & then starting engine
Motored into Bradwell OK
2 weeks later started engine & water came out immediately
Sailed to Ostend & no water until I did the same trick of laying boat over
berthed for 24 days & water came out strongly & immediately
Sailed to Flushing & no water again
The sea water pump recently had new shaft & seals fitted & there is no leak. The pipes & all water connections have been checked. I do not open & close the sea cock between the use mid season

Any ideas as to why all this is happening after I sail the boat please

 

[TSB240]

Check that you don't have mussel or similar growth inside the sail drive at the stop cock inlet. This can block your water inlet enough to block water flow as you describe. Shut cock remove pipe open cock and rod through. Expect slight fountain effect! and possibly small amounts of broken shell in filter. Steve

 

[RichardS]

Are you putting loads of silicon grease on the lid of the filter housing when you replace it. Your symptoms are typical of air ingress upstream of the water pump and the filter lid is the usual culprit, even if it looks OK.

Richard

 

[Tranona]

First thing to do is take the hose off he seacock on the saildrive end to check you are actually getting water in. If the cock is open and no water the blockage is in the leg. However, if you have manged to get it primed then If water there, then the problem is further along. Prime suspects are leaking cap of the water strainer or loose hose connections as Richard suggested. if not then the seawater pump, such as impeller of worn face plate.

 

[Daydream believer]

Are you putting loads of silicon grease on the lid of the filter housing when you replace it. Your symptoms are typical of air ingress upstream of the water pump and the filter lid is the usual culprit, even if it looks OK.

Richard

But if it worked immediately after a 24 day lay off would that still be the problem??

 

[Tranona]

But if it worked immediately after a 24 day lay off would that still be the problem??

Sounds like air is getting in somewhere, either the seal on the cap or perhaps a crack. These things can be infuriating to track down. I once had a similar intermittent problem that eventually traced to an otherwise healthy looking jubilee clip that had a stripped thread.

 

[scottie]

The water comes in through the vertical hole in the nose of the older sail drives rather than the slots
You should be able to clear this with a rod whilst out of water
Pumping air in the water inlet pipe with a dinghy pump is also useful

 

[runningman]

Check that you don't have mussel or similar growth inside the sail drive at the stop cock inlet. This can block your water inlet enough to block water flow as you describe. Shut cock remove pipe open cock and rod through. Expect slight fountain effect! and possibly small amounts of broken shell in filter. Steve

Or remove hose from filter (not saildrive), raise hose above water level and rod through with no slight fountain effect. Fit a longer hose if the top is still below the water line. Much drier and not as stressful!

 

[RichardS]

But if it worked immediately after a 24 day lay off would that still be the problem??

It's very much a hit and miss affair depending upon how tightly you screwed down the lid last time, especially if there is a crack in the lid which can be made worse rather than better by overtighening. The only way to rule it out is to examine it carefully for tiny cracks in the plastic or rubber seal and then put on loads of grease and nip it up ..... but not too tighly.

If the problem goes away, you've sorted it.

Richard