Seawater system cleaning

[cmedsailor]

How important is the annual clean up (flushing) with fresh water of the seawater system? Is it something “good to make” or a “must do” thing?
I got the boat out of the water about a month ago but couldn’t run the engine until a couple of days ago due to some other repairs. Now that I can run it will a couple of buckets with fresh water make any difference to the system, keeping in mind that after so many days any salt will be crystallised?
Thanks

 

[vyv_cox]

I wouldn't go so far as to say that it's essential, but well worth doing. The problem is that when the coolant runs out of the engine it leaves some salt behind. This attracts water absorbed in the air, creating a local corrosive cell. Unlike the situation when the engine is full of water, an internal anode cannot protect against these corrosive cells. Rapid corrosion can occur locally, leading to pits inside the coolant jacket.

Running some fresh water through, even at this late stage, will help.

Having said that, my old raw-water cooled Bukh engine had this treatment from me in its last five years, but almost certainly didn't for its previous ten or so. Although water draining from the coolant chamber was rusty there was no evidence that it had done severe damage.

 

[VicS]

I agree with Vyv, it's not essential, but well worth doing.

BUT leaving the system wet but empty, even wet with fresh water, will lead to more corrosion that if left full of fresh water. Better therefore to flush through with a corrosion inhibitor, eg antifreeze, and preferably leave full with an inhibited mixture, antifreeze where freezing could occur.