Raw water cooling

S

slipknot

Well-Known Member
Joined
28 Nov 2003
Messages
548
Location
South Coast
Visit site
I am considering buying a boat which has a Yanmar 2GM20 diesel which is raw water cooled.

My previous boats have been freshwater cooled with a heat exchanger and I have been happy with this arrangement. The thought of sea water in the engine does not really appeal as I would have thought that it may have had some disadvantages. Such as coating of internal components leading to poor cooling performance, and worse still, corrosion reducing engine life.
Any informed views/experience of this you can share?
Ian
 
Change it if you can as everything will corrode quicker when raw water cooled - especially if left for long periods without flushing through with fresh water. Also, the engine runs cooler, which is less efficient and means you can't heat domestic water from the engine.
 
[ QUOTE ]
I would have thought that it may have had some disadvantages. Such as coating of internal components leading to poor cooling performance, and worse still, corrosion reducing engine life.


[/ QUOTE ] Yes most likely.

If the engine has an anode make sure you replace it regularly.

When laying up drain out the salt water, flush it by running on fresh water until the thermostat has opened and run for long enough to ensure all the salt is flushed out.
Then drain down again and fill with antifreeze mixture.

The antifreeze does not do pump impellers any favours so don't be tempted to use it super strong and if the impeller is due for renewal do it at the end of the winter.

Never seen it mentioned in this context but Zn anodes are not suitable for fresh water as they become coated with a layer of oxide (?) which then renders them ineffective so again change at fitting out time rather than laying up time.
 
"
The antifreeze does not do pump impellers any favours so don't be tempted to use it super strong and if the impeller is due for renewal do it at the end of the winter."???????????????????????????????????????????????????????????????

Ive never heard of anyone putting antifreeze in a boats engine???In the north all the boats are out and in the south it never freezes not even in the UK??Dose it?
 
The reason for this - well at least my reason for this is that I flush the raw water side with fresh water on lay up which obviously replaces the salt water. So to prevent that fresh water freezing, I finally add a mixture of anti-freeze to the final flush and leave it in the 'system' until the beginning of next season.
 
hi, my boat has the yanmar 2gm20 engine which has, at some time in the past, had a conversion to freshwater cooling. This consists of a heat exchanger and a small johnson electric pump and a plastic header tank. The manufacturers of this kit are Martec but I'm not sure if this is still available. The cooling water heats the domestic hot water via a calorifier in the normal way. This generally works very well except for two problems. Firstly, the heat exchanger must be a bit on the small side as if you really push the engine it will overheat after a while. Secondly, the system relies on the electric pump. However, I have had the boat for several years without any problems and the hot water is very nice. My previous boat had a bukh raw water cooled engine, apart from having to change the engine anodes every year, and an occasional exhaust elbow, she was completely trouble free. She was over 20 years old with the original engine when I sold her. I think, like almost everything else where boats are concerned, its a matter of the compromise which suits you best.
 
[ QUOTE ]
Ive never heard of anyone putting antifreeze in a boats engine???In the north all the boats are out and in the south it never freezes not even in the UK

[/ QUOTE ] It can freeze in the UK even in the south. Filling the system with antifreeze is standard procedure, and more important if the boat is out of the water than if still afloat. (An indirectly cooled engine would normally be filled with anti freeze anyway)

It you are in a area where it is not going to freeze then fill with a corrosion inhibitor (antifreeze contains an inhibitor). Don't leave drained but wet, that will cause the most amount of corrosion.
 
Raw water cooling is not as bad as might be supposed. If the engine in your next yacht is in good order, then it will do you fine, provided you winterise it as advised on an earlier post ( ie drain the salt water and fill with antifreeze which has rust inhibitor). Also it is not true that raw water cooling systems do not heat the domestic water sufficiently. It does just fine on my yacht. In short, don't be kneejerked into needless expense in changing your engine. /forums/images/graemlins/cool.gif
 
I converted my 1GM 10 to fresh 7 years ago
Built a water pump housing from a alloy block following plans in an old PBO article, fitted a fiesta pump into this housing driven from the altenator belt (for the fresh water side)

Fitted a heat exchanger from a gas combi boiler (about the size of a large flask. I take these out at work now and then so have built up a stock as I did not know how they would last but am still on the first one.


A small header tank from a mini metro I think (with a small hole in the top to prevent pressurization)

And replaced the temperature warning sender to fresh as it runs slightly hotter now.

no problems and it has to be better for the engine.

pete
 
There are thousands of boats around with raw water cooling. Their reliability and life are just as good as a fresh water cooled engine. I know of several that are at least 25 years old, with no problems. I replaced my raw water cooled Bukh when it was about 20 years old, it had no problems associated with the coolant, just getting rattly and a bit undersized.

I also know of several fresh water cooled Volvos that have been converted back from original fresh to raw water cooled to overcome the horrendous unreliability of the push fit piping that they come with.

And before someone starts telling you that you can't run a calorifier with a raw water cooled engine, you can. You just have to do it properly and you will enjoy (?) scalding hot water within 15 minutes of start-up.
 
If the engine is designed for raw-water cooling, then there is no advantage to fresh-water cooling. As another poster has pointed out, many thousands (I would guess the majority) of boats have raw-water cooling; the engines wear out or fatally fail from other causes before there is trouble from the cooling system. The additional complexity of the fit simply gives you more places for something to go wrong! And of course,you can perfectly well run a hot-water calorifier from a raw-water cooling system
 
I have a martek cooling kit on my 2gm20, they were sold by aquafax marine. The company who makes them can be found online.
The heat exchanger used is the same for the 1gm10 and the 2gm20, mine has worked without any problems now for seven years, as the instructions say, its a good idea to flush a previously raw water cooled engine several times to get best cooling.
I also fitted a temp gauge to keep an eye on the temp which never goes above 80 degrees, i also get a better mileage
 
my previous boat had a 2GM20 raw water cooled engine which I had eventually to replace. so I took it to bits and was astounded at the good condition of the block and its waterways after 15 years use. so impressed that I replaced it with another raw water cooled engine, and the yanmar dealer who supplied me with the new one gave me several hundred pounds part ex for the old one. He's a very reputable engineer and his view was that the engine could be re-conditioned to be as good as new ( I took the safety first course of a new one because at that time I was planning to take the boat to the eastern med and wanted the security of new)

personally, I wouldnt worry at all about a raw water cooled yanmar. they are true marine engines not converted earth moving kit, and they last well.

for what its worth, the insides of my current volvo 2003 raw water cooled look equally good. what seems to happen is that the passageways get lined with a deposit of carbonates which together with a layer of iron oxide seperates the iron metal from the water I'm guessing in saying this - dont know if anyone on the forum has hard facts?
 
[ QUOTE ]
a deposit of carbonates together with a layer of iron oxide seperates the iron metal from the water I

[/ QUOTE ] It is almost certainly not a layer totally impervious to water that will afford protection against corrosion and it will definitely reduce the heat transfer to the water coolant. Cooling is what the cooling system is all about. Don't be lulled into a false sense of security by a normal temperature indication on the gauge. The water temperature will be controlled by the thermostat and the reading will remain normal until the waterways become so fouled that insufficient water flows to conduct the heat away. The metal temperature, and that is what is important, will be higher than it should be under the layers of calcium carbonate and iron oxides.

I'm not familiar with the Vovo 2000 series but i can tell you that scaling and corrosion in the old MD11 engines becomes a major problem after 20 or 25 years service.

I'm with you though on not worrying unduly about raw water cooling in the short term but in the long term indirect cooling must be a better choice.
 
You must log in or register to reply here.

Share this page

Top