Seawater system

[carlager]

The seawater intake and output works fine on the the engine -abYanmar 3GM30F - in our Oceanis 36cc is running.

Recently I discovered that seawater strainer placed above sealevel and on highest point in the seawater system is empty when engine is turned off.

Does anybody know if there should be seawater in the strainer when is turned off ?

 

[Beneteau 321]

Our 1997 Beneteau 321 with 3GM30F is set up the same way.When engine is not running there will not be any water in the strainer as the strainer will drain back into the raw water intake line to the height of the water outside the boat.The engine side will still be full.When the engine is started raw water pump will draw water up into the strainer and through the engine.
As a side note I usually remove the top of the strainer to inspect the strainer basket for debris numerous times during our sailing season ,especially if we have been an area with a lot of weeds and shallow water (sailing on the Saint John River ,New Brunswick Csnsda

 

[Captn TJ]

Our 1997 Beneteau 321 with 3GM30F is set up the same way.When engine is not running there will not be any water in the strainer as the strainer will drain back into the raw water intake line to the height of the water outside the boat.The engine side will still be full.When the engine is started raw water pump will draw water up into the strainer and through the engine. As a side note I usually remove the top of the strainer to inspect the strainer basket for debris numerous times during our sailing season ,especially if we have been an area with a lot of weeds and shallow water (sailing on the Saint John River ,New Brunswick Csnsda

Same on our 423 with a Volvo. No water in the strainer when the engine is not running.

 

[Ron20324]

Being plastic-type material, if it was below the waterline and cracked you'd be flooded. It's somewhat like the vents in heads and other water lines.

 

[carlager]

Spoke to a Yanmar dealer. He told me that if the seafilter house is empty when the engine is not running there is a leak in the raw water system. This means that the impeller will suck in air during start up. This will reduce the lifetime of the impeller. The great risk is however that the exhaust hose will overheat and leak due to insufficient raw water intake.

 

[DougM]

Someone is getting conflicting information. I tend to agree with those who report no water or only residual water in the strainer. Its the high point in the system and it probably should drain back through the exhaust when the engine is shut down. I cannot recall any boat that I have had that had water in the strainer when I opened it up to clean it. If the Yanmar dealer states that this would indicate a leak in the system, there must be a lot of us with that problem.

 

[joker460]

I'd have to agree with the Yanmar Dealer, at least with my system(3GM30F).
With the engine off, there is water in the hose from the impeller to the filter, the filter has about an inch of water in it, and the hose from the filter to the raw water inlet is full.

When I open the filter cap, the residual water drains back to the raw water inlet. This releases the suction in the line.

 

[carlager]

When the lid on the strainer is loosend there is no longer vacuum In the seawater system. This means that water in the strainer will run back to the seawater level. If the strainer is located above seawater level there will be no water in the strainer when you remove the lid and "break"' the vacuum in the system. If you close the seacock on the rawwater intake and then remove the lid there will be water in the strainer IF there are no leaks in the system. If not the rawwater system is sucking air which means that the system is not cooled as required.

 

[Grouperhound]

Since the inlet is below water and the exhaust is above, the water will syphon back to the inlet. The pump impeller would act like a seal, to some extent, but whether it's enough to prevent drain back is unlikely. The pump should still have enough water in it to lubricate the impeller until it gets continuos flow.