Winter afloat. Will the block crack?

[35mm]

I'm on the south west coast (UK) and have a drying mooring on a salt water (not too brackish) estuary. I'm leaving my boat in the water over the winter, and hope to get out on her for a winter sail and spot of fishing from time to time.

My engine is an old (but reasonably good) Volvo MD1B - 10hp single cylinder, diesel with raw water cooling. I've started wondering about the safety of the engine block if the temperature gets below freezing this winter. In the past I've had outboards and haven't had any freezing problems with them as they tend to drain when left cocked. My father had diesel inboards and some times wintered his boats on the mooring, but he's no longer alive to give me his pearls of wisdom. The internet seems surprisingly sketchy on this subject. I recently purchased 10ltr of propylene glycol, for the water tank and heads, and was thinking I might have to flush some through the engine each time I run it through the winter, which would be a pain in the neck. This evening I was talking to a local fisherman friend and asked him what he does to protect the raw side of his closed/fresh water cooling system. "Nothing!" he said. "Just make sure it don't get clogged up with muscles and clams." I told him about my engine, and he said if it's raw water cooled it should be fine, and he'd never heard of any boats on the river having problems with freezing. So now I'm totally confused. Sea water freezes at about -2C and apparently it doesn't freeze the same way as fresh water. The fresh water within it starts to freeze but leaves pockets of brine which won't freeze until the temperature gets much lower. So does this mean it might go slushy, but not solid enough to crack the block? What are people's opinions and experiences of raw cooled engines left afloat in sea water over the winter?

 

[rob2]

It's good that you've got concerns about this - there are no absolutes as all the variables are unpredictable, so keep it in mind over the winter. When the boat is afloat, the seawater will help keep the boat's temperature up, frosty air will chill the engine though. As you say, seawater doesn't freeze the same as fresh, and I've even seen slushy ice ejected from the exhaust of a boat on starting! The up side is that it means that the internal pressure from expansion is likely to be less. You might like to consider draining the block (and leaving the drain open) during really cold snaps - leave yourself a note to remind you to close it before starting.

Rob.

 

[MASH]

How can your block crack if you use antifreeze correctly? Use of antifreeze is the only factor, nothing else has any bearing on ice damage to the block. Seawater is irrelevant as it is nowhere near the block. Anyway it never falls below zero or you'd be in pack-ice which is rare in UK so in really cold weather the seawater environment will be ensuring your engine never gets near to the antifreeze's limit

Its up to you to decide what temperature you want protection down to but -10 would be more than adequate, even -15 is easily achievable with standard antifreeze.

There is no problem to worry about.

 

[Chris_Robb]

If there is a really cold snap forecast, you may just want to run 50% antifreeze through the water system. Disconnect your intake, fill a bucket with fresh water, run for a couple of bucketfulls, then a gallon of 50/50 antifreeze - stop when bucket dry. Antifreeze also has a corrosion inhibitor, so best to winterise the engine this way rather than training down.

 

[pvb]

Seawater is irrelevant as it is nowhere near the block.

Errr... he has a raw water cooled engine. It's full of seawater.

 

[Tranona]

How can your block crack if you use antifreeze correctly?

Its up to you to decide what temperature you want protection down to but -10 would be more than adequate, even -15 is easily achievable with standard antifreeze.

Sea water is nowhere near the block so is not a factor.

There is no problem to worry about.

Not the case. The OPs engine is seawater cooled so is full of seawater. You cannot realistically use anti freeze because the water flows through the engine and back into the sea. Although it is common to leave a seawater cooled engine full of anti freeze if it out of the water, it is not sensible to use it when afloat as it is harmful to the environment if pumped out (as it will be).

To the OP - nothing to worry about. Turn the seacock off just before you stop the engine and it will pump most of the water out. Remember to open it before you restart. I wintered my seawater cooled Yanmar in the water for 20 years (in Poole) and never had a problem.

 

[pvb]

Turn the seacock off just before you stop the engine and it will pump most of the water out.

How does that happen? Where does the air come from to replace the water?

 

[Avocet]

Depends very much on the design of the engine, I think. If it is such that all the voids end up with some air in them, you'd probably be fine. If it ends up with only the higher ones having their water expelled, it could be a problem. I've never had a problem in seawater (and the harbour in Whitehaven can have a lot of freshwater in it during times of high rainfall). It froze a few years ago, and I don't think any of the boats suffered. However, I've had problems in freshwater:

That was the cast iron cylinder barrel.

I agree that running a strong antifreeze solution through (and catching what comes out of the exhaust) is the best for the engine. Draining it always leaves "puddles" in the various hollows that accelerate corrosion.

 

[testmonkey]

if the boat is kept in water then no problems with the do-nothing approach. Saildrive or direct shaft will conduct enough "heat" from the seawater below the boat to keep engine block temperature at, or slightly above 0 degrees Celsius, so no risk of freezing. Problems would only start if you get solid ice also below the propeller but that is unlikely in the UK... Most frost damage actually happen when winter is coming to an end and what was frozen solid starts to thaw, this is when biggest volume expansion happens and pipes and blocks burst etc.

So - if in water no problems. However, if the boat is on the hard - no warm seawater is around and then yes you will get frost damage unless you drain all the water or replace with proper anti-freeze mix.

 

[pvb]

if the boat is kept in water then no problems with the do-nothing approach. Saildrive or direct shaft will conduct enough "heat" from the seawater below the boat to keep engine block temperature at, or slightly above 0 degrees Celsius, so no risk of freezing. Problems would only start if you get solid ice also below the propeller but that is unlikely in the UK... Most frost damage actually happen when winter is coming to an end and what was frozen solid starts to thaw, this is when biggest volume expansion happens and pipes and blocks burst etc.

So - if in water no problems. However, if the boat is on the hard - no warm seawater is around and then yes you will get frost damage unless you drain all the water or replace with proper anti-freeze mix.

So, as the OP said he has a drying mooring...

 

[35mm]

Yea I was wondering about the dry mooring bit. She dries out for about 2 hours around low springs and sits on the mud.

I did look the other day to see if I could find a block drain, and I undid a bolt I found on the side and water came out so that was that, however it's right behind the dynastart and very tricky to get to. I have propylene glycol which is non toxic antifreeze for fresh water tank etc. I can run some through the engine if needs be, but again that's fiddly to do every time I use the boat. Having read some of your replies I'm now not so worried about leaving it with sea water in the block, but would still be interested to hears other's experiences with this.

 

[BabaYaga]

Although it is common to leave a seawater cooled engine full of anti freeze if it out of the water, it is not sensible to use it when afloat as it is harmful to the environment if pumped out (as it will be).

Propylene glycol is not considered harmful for the environment, provided it does not contain anti-corrosion chemicals, dye etc (should not be the case if intended for water tanks).

 

[savageseadog]

It's helpful to disconnect the water pump outlet hose

 

[vyv_cox]

Very few boats left in the sea in UK winters will come to much harm, even on a drying mooring. Minimum seawater temperature in your area rarely falls below 10C, see here. The likelihood of freezing within a few hours at low tide is very remote indeed.

If you are really worried, drain the block. Contrary to what has been said above, engine designers are not stupid, even when yours was designed and the drain cocks will empty it. You might want to think about draining the exhaust trap but I doubt that it will give you any trouble. There have been stories of water pumps cracking when frozen, which again seems unlikely in your area, but you could loosen the cover screws to drain it if you were really concerned.

 

[35mm]

Thanks for your comments. They have made me more confident about the "not bothering too much" technique. All considered, I think the engine will be all right, but if it comes to a severely cold spell I might chuck some propylene glycol into it. Should probably do the same with the heads?

 

[alahol2]

... I have propylene glycol which is non toxic antifreeze for fresh water tank etc....

Not sure I understand the logic of this. Surely you will have to get the antifreeze out of the water tank come spring, which will involve draining it. Why not drain it now? Or is the antifreeze drinkable?

 

[35mm]

Not sure I understand the logic of this. Surely you will have to get the antifreeze out of the water tank come spring, which will involve draining it. Why not drain it now? Or is the antifreeze drinkable?

Have drained the tank, but there will always be some water left in there, so adding propylene glycol will stop that from freezing and causing damage. Propylene glycol is non toxic (same stuff they use in electronic cigarettes and smoke machines etc.) so come spring time, I'll flush it out, fill up and all will be good.

 

[Avocet]

I don't think there would be any danger of damage by freezing with a drained block. The pockets of water that are left will have plenty of room to expand. I'd be more worried about them causing corrosion, locally, because the anodes won't be immersed.

 

[GrahamM376]

Who knows what the temperature may drop to this winter. A couple of gallons of antifreeze costs a lot less than having to replace an obsolete broken engine.

 

[vyv_cox]

Who knows what the temperature may drop to this winter. A couple of gallons of antifreeze costs a lot less than having to replace an obsolete broken engine.

If you follow the thread and the link I posted, the OP is in SW England. The boat will remain afloat on seawater whose temperature has not dropped to anywhere near freezing in the past ten years at least. There is no risk of his engine freezing.

My view, which I have posted several times, is that filling a raw-water cooled engine with antifreeze is hit or miss at best and a considerable hassle, especially as he would have to do it every time he uses the boat, which he intends from time to time. Far better to drain it. OK, there may be an increased corrosion penalty but these engines are heavily cast with a big corrosion allowance. Flushing with fresh water before draining would help a little.

I see the link I posted seems to be down. It's the Defra seawater temperature records for Plymouth. Minimum from memory was about 8C for one month a couple of years ago.