Doesn't sound 'normal' to me.. it also means your impeller must run dry on every startup for a moment.. Is there room to relocate it? Ours is also below waterline and always 'primed'.The seawater strainer placed above sealevel and on the highest point on the seawater system on our Yanmar 3gm30f is empty when the engine is not running.
Is this normal ?
Faster is absolutely correct the impeller will run dry for a short period. Even if it is downhill from the strainer to the pump and that section of hose is full of water, the air in the empty strainer will get sucked through the impeller.Are you saying the strainer is after the impeller? If the impeller is (properly) downstream of the strainer then it's pulling air for a bit until the system is once again flooded...
Glad you got it worked out. I'd recommend you pull that impeller for a close inspection and if possible reposition the strainer as low as you can get it, preferably below waterline (difficult in many sailboats).You are right. The strainer should be full when the engine is not running. Greased the O-ring on the lid to the strainer. Now there is vacuum when the engine is not running and water In in strainer
The OP reported the issue resolved in post#7I agree with minnewaska there must be a loose fitting or opening somewhere in the line that is allowing for the vacuum in the line. Does it immediately empty, or does it take its time? Does that water run back to the engine or through the exhaust line? Speaking of which, you may want to check the exhaust line and make sure that it doesn't exit below the strainer. That would create the vacuum issue you are experiencing.
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NO, its not normal as the contents of the strainer can drain-back and thus leave the strainer body full of air. If that slug of air reaches to the raw water pump, the pump may have difficulty 'priming itself' all the way to the pump ... especially as the pump normally wears/ages and the 'sides' of the pump vanes no longer 'seal' the impeller to the pump body vs. air. Once the pump and strainer are fully filled with water by the action of the pump, the water in the pump will make the proper seal to the sides; if the pump 'air leaks' past the impeller sides you may be running 'dry' pump for a long interval.The seawater strainer placed above sealevel and on the highest point on the seawater system on our Yanmar 3gm30f is empty when the engine is not running.
Is this normal ?