Closed Cooling System

[Cruising Roo]

Me again. What are the "brains trusts" opinion on a closed cooling system on a small inboard (with leg) engine. Also, can the boat be operated out of the water. Thank you for your replies

[ranger58sb]

Somewhat more complicated, due to extra components... but better choice, especially for saltwater use.

Yes, as long as you provide cooling water while running. You're thinking about flushing after use? That's not uncommon...

-Chris

[tkeithlu]

Ditto. You can start the engine dry just to see that it starts, and shut it down promptly. The lack of cooling water only becomes an issue when the engine heats beyond the temperature that would occur with coolant present.

[Tin Tin]

We would, close the sea water intake, take the lid off the strainer and put a hose in, start the engine and adjust hose to feed water in at same rate it goes down. This way you can not over pressure the system and force water back through the elbow into the engine.

[rslifkin]

Originally Posted by tkeithlu

Ditto. You can start the engine dry just to see that it starts, and shut it down promptly. The lack of cooling water only becomes an issue when the engine heats beyond the temperature that would occur with coolant present.

Not necessarily. Usually with no cooling water you'll burn up the exhaust hoses (and possibly damage fiberglass mufflers) long before you overheat the engine. Not to mention the failed impeller from running it dry.



Personally, I wouldn't start an engine dry unless it was fresh out of maintenance to confirm it'll start, impeller lubed with something and then shut it down as soon as it fires.

[Cruising Roo]

Thank guys. This will prove just how much of "virgin" I am but from what I can gather from Dr Google although there are articles that are either not clear or have left me wondering if I really have any idea how they work... I do not. So am I right that a 'closed system' runs like a car with coolant running through the engine BUT still uses raw water to cool the heat exchanger? If that is correct, surely no system allows salt water to run through the engine!! Just the thought of that makes me cringe. Thanks. Darren

[Ballsnall]

Originally Posted by Cruising Roo

So am I right that a 'closed system' runs like a car with coolant running through the engine BUT still uses raw water to cool the heat exchanger?

That's correct, engine block has closed system with coolant and raw water through heat exchanger

If that is correct, surely no system allows salt water to run through the engine!! Just the thought of that makes me cringe.

Incorrect, some engines run raw water through the engine (no heat exchangers) outboard engines are a good example but also applies to inboards thought no so common these days with modern engines.

Another common method is a closed system with keel cooling, this is the system most similar to a car. Instead of a heat exchanger there is a keel cooler (which is a type of heat exchanger) that circulates through the engine block. This is a common system on steel vessels especially work boats and is commonly used with dry exhaust but can have wet exhausts as well.

[Cruising Roo]

Thanks Balsnall. Informative reply. yes I understand with outboards and have owned hundreds BUT, you can flush an outboard. Are these raw water systems just left with salt in the engine? This is not important but i love to learn about anything 'marine'. Cheers. Darren

[Benz]

Originally Posted by Cruising Roo

Thanks Balsnall. Informative reply. yes I understand with outboards and have owned hundreds BUT, you can flush an outboard. Are these raw water systems just left with salt in the engine? This is not important but i love to learn about anything 'marine'. Cheers. Darren

I have a boat with a tiny Yanmar diesel that cools directly with seawater (no heat exchager). When winterizing I flush the system by taking the intake hose off the seacock and holding it in a bucket of fresh water that's being replenished by a hose.
Then I fill the bucket with antifreeze and run that all the way through till it comes out the exhaust, then I'm done.

[Cruising Roo]

Thanks Benz but that is once a season. Evidently marine engines can cope with the salt which is extraordinary to me. The cooling lines through the engine must be lined with something pretty "resilient" of the salt water. As mentioned, I am very much a virgin on inboards and the topic is interesting...well to me anyway. It would be very interesting how merchant ship engines cope with salt water. Somehow i don't think they would ... pop the engine out to flush it !!

[Fore and Aft]

Cruising Roo I bet your stern leg is never flushed if it's left in the water. Leaving saltwater in an engine is not that bad as long as the anodes are regularly changed. I see plenty of older Yanmar diesels that are saltwater cooled. Just last week I surveyed a yacht with a 44 year old 3QM diesel raw water cooled and it was still running fine. Same with outboards, plenty of cats have outboards in pods under the cockpit floor and they never get flushed. Regular use and maintenance is the key to longevity.
I take it you have a MerCruiser so you should be able to get some earmuffs to put on the leg so you can run the engine out of the water.
Cheers

[Benz]

Originally Posted by Cruising Roo

Thanks Benz but that is once a season. Evidently marine engines can cope with the salt which is extraordinary to me. The cooling lines through the engine must be lined with something pretty "resilient" of the salt water. As mentioned, I am very much a virgin on inboards and the topic is interesting...well to me anyway. It would be very interesting how merchant ship engines cope with salt water. Somehow i don't think they would ... pop the engine out to flush it !!

Saltwater corrodes steel more when the steel is dipped and dried over and over again: look where steel dock pilings rust away--not ten feet under water, but at the waterline.
A cooling system with only water in it and no air will rust a lot slower than one where salt dries and washes continually.
Big ships use coolant with heat exchangers, so saltwater never enters the engine. Sometimes a keel cooler, mentioned above, pumps the coolant through a run of pipes outside of the boat (attached to the keel), making the entire ocean the heat exchanger.

[Cruising Roo]

Originally Posted by Fore and Aft

Cruising Roo I bet your stern leg is never flushed if it's left in the water. Leaving saltwater in an engine is not that bad as long as the anodes are regularly changed. I see plenty of older Yanmar diesels that are saltwater cooled. Just last week I surveyed a yacht with a 44 year old 3QM diesel raw water cooled and it was still running fine. Same with outboards, plenty of cats have outboards in pods under the cockpit floor and they never get flushed. Regular use and maintenance is the key to longevity.
I take it you have a MerCruiser so you should be able to get some earmuffs to put on the leg so you can run the engine out of the water.
Cheers

Thanks. Well as mentioned, I have only ever owned outboards and I agree that if they are used all of the time then flushing is not important due to the water "constantly" moving through them. I am sure you are right about engines clearly being fine because there are so many of them. As mentioned,
I just enjoy learning and i am far from making any bold statements. I am also aware that a boat with a leg does not do too well if left permanently in the salt water but I am sure there are. Time for this old rooster to go and get his beauty sleep cos sure as hell...i need it

[Ballsnall]

Originally Posted by Cruising Roo

Thanks. Well as mentioned, I have only ever owned outboards and I agree that if they are used all of the time then flushing is not important due to the water "constantly" moving through them. I am sure you are right about engines clearly being fine because there are so many of them. As mentioned,
I just enjoy learning and i am far from making any bold statements. I am also aware that a boat with a leg does not do too well if left permanently in the salt water but I am sure there are. Time for this old rooster to go and get his beauty sleep cos sure as hell...i need it

Outboards and legs are built with corrosion resistant materials and flushing is not done for corrosion control, it is meant to help prevent salt build up internally that could potentially limit the cooling flow. Legs and outboards for that matter, left in the water 'dont do well' is usually due to marine growth and or electrolysis. For raw water cooled inboards they are all cast iron engines which is quite corrosion resistant and also not prone to electrolysis either.