Winterising Raw Water Circuit

[Oily Rag]

I've left the engine's fresh water circuit with plenty of anti-freeze , but have only drained down the raw water system upstream of the engine.

I've left the system downstream of the exhaust with the seawater it had in it when the boat was lifted out for the winter. Should I have drained it, flushed it with fresh, flushed it with old anti-freeze or flushed with a strong salt solution to prevent frost damage?

 

[Skylark]

I’m sure that there are plenty of boats lifted each winter without owners touching the raw water system to no ill effects.

My routine is to flush the system. With the boat in the slings, as soon as she clear of the water I start the engine and pour a bucket of fresh water into the strainer followed by 4 litres of cheap, ready-mixed antifreeze. I leave the impeller in place over winter and replace it in Spring as part of prep for launch.

 

[Tranona]

Really no need in most of the UK to do anything with the raw water circuit. The small amount of seawater in the exhaust water trap is highly unlikely to freeze. Some have drains at the bottom if you are worried about it. If the boat is in a location exposed to the late winter, early spring Easterly winds then there might be a possibility of freezing, but even then unlikely.

 

[jwilson]

I do much as Skylark does, only after liftout but before any frosts arrive. In fact I was planning to do it today. The last few winters have been so mild we barely had frost here in Cornwall, but some years back we did have a prolonged hard freeze up.

The cost difference of some antifreeze vs a new heat exchanger is very significant, and some raw water could get left in there....

 

[[2574]]

But always the worry is pumping the anti-freeze directly in to the sea when you start your engine in the spring……at least I worry about it.

 

[Stooriefit]

Like Skylark and jwilson I also flush through with fresh water and then antifreeze, leaving the latter in over the winter. I'd rather not have worries about the potential damage of (a) saltwater sitting needlessly over the winter months and (b) the slight chance of freezing. As to what happens in the spring I flush the antifreeze back out before going in the water thereby avoiding Robih's situation.

 

[vyv_cox]

I bought my boat with a 10 year old raw water cooled Bukh in it 25 years ago. This was long before things like flushing engines were commonplace or discussed on forums. I doubt very much that the previous owners ever flushed it and I did not for probably 10 years. Despite that it never froze nor seemed to have suffered much from internal corrosion.

Now I have an indirectly cooled Yanmar I flush it with 11 litres of fresh water via the Vetus strainer at season end. Removing the impeller will drain it completely, nearly all tubing is rubber and the heat exchanger will drain aft. I see no reason to go further.

 

[Skylark]

But always the worry is pumping the anti-freeze directly in to the sea when you start your engine in the spring……at least I worry about it.

Changing the impeller prior to launch should allay your fears

 

[NormanS]

My exhaust system seems to contain a large volume of water in its various parts, waterlock, muffler, pipework etc. OK, I'm in Scotland, where we get weather, but if the boat is ashore for the winter, I definitely flush the exhaust system with antifreeze. It's just part of my normal winterizing, and simple to do. The last thing I want is to find a split caused by freezing, in any part of the exhaust.

 

[Elessar]

I've left the engine's fresh water circuit with plenty of anti-freeze , but have only drained down the raw water system upstream of the engine.

I've left the system downstream of the exhaust with the seawater it had in it when the boat was lifted out for the winter. Should I have drained it, flushed it with fresh, flushed it with old anti-freeze or flushed with a strong salt solution to prevent frost damage?

If you’re boat is in the water don’t worry. The water will keep the boat warm enough.
If it’s not in the water put it back in and enjoy winter sailing.

 

[Daydream believer]

I put the water inlet pipe into a tub of fresh water, start the engine. then to keep it topped up I put the spray hose from the shower in the tub & drain the fresh water from my tank. I finish off with 5 litres of antifreeze, stopping when i see it exit from the exhaust. I prefer to flush the salt from the system annually if possibly..
Some of the fresh drinking water goes through the heads whilst I am at it. It is a bit cleaner when I service the pump & check pipes for calcium build up. The rest of the fresh water from my main tank is drained by disconnecting pipes- particularly at the water heater etc
So I do 3 jobs in one go