Why have a thermostat on a raw water cooled engine?

[LittleSister]

Bukh suggests that indirect cooling is only required if the engine does more than about 500 hours per annum (but doesn't state the rationale for that recommendation).

The Bukh DV36 Manual specifies the working temperature as 50 to 70 degrees C for direct cooling, and 70 to 95 degrees C for indirect cooling.

By contrast the Bukh DV10/24 Manual specifies 50 to 75 degrees C whether direct or indirect cooled.

 

[jamie N]

I installed a heat exchanger, and an extra pump, to convert it to fresh water cooling, which was very successful.

That's what I've done, yet to be tested of course, but it should be OK. What can possibly go wrong...........!!

 

[TC Tuckton]

Another case for the line I've been pushing re the benefits of flushing engines with fresh water, preferably hot, after each run, using a supply from the calorifier via the galley pump and a stopcock. My boat is indirectly cooled but I've no doubt the heat exchanger and exhaust elbow benefit, just as any outboard does. It only takes a minute after each run.

On a directly cooled cast-iron engine it seems intuitively that it might be even more beneficial, both to protect against rusting and as you point out, salt crystalisation. A cast iron engine sitting for days, weeks or months with its waterways full of brine seems not a good idea.

Another case for the line I've been pushing re the benefits of flushing engines with fresh water, preferably hot, after each run, using a supply from the calorifier via the galley pump and a stopcock. My boat is indirectly cooled but I've no doubt the heat exchanger and exhaust elbow benefit, just as any outboard does. It only takes a minute after each run.

On a directly cooled cast-iron engine it seems intuitively that it might be even more beneficial, both to protect against rusting and as you point out, salt crystalisation. A cast iron engine sitting for days, weeks or months with its waterways full of brine seems not a good idea.

Perhaps there is an advantage in having a mooring 2 miles up river.

 

[lw395]

Take care to distinguish between 'salt' and 'salts'.
Common salt, sodium chloride, the stuff that is in sea water. More soluble at higher temperature.
Other salts include compounds of iron, aluminium or whatever, more likely to be formed at higher temperatures.
There is also calcium and other stuff about.
Your engine will corrode more at higher temperatures, the scale produced may then trap salt.
There is calcium in sea water, enough for your engine to scale up like a kettle if you run it hot enough for long enough.
I guess that varies a lot from the Solent Brown to the Gin Clear Med or whatever.

It's not so simple as rinsing out the sodium chloride after use. But that helps. Outboards which don't get rinsed for instance end up full of corrosion. Then full of holes.

It's surprising that raw water cooling works at all really, but like Victorian piers, cast iron can be fairly long lived in seawater.

 

[Refueler]

Bukh suggests that indirect cooling is only required if the engine does more than about 500 hours per annum (but doesn't state the rationale for that recommendation).

The Bukh DV36 Manual specifies the working temperature as 50 to 70 degrees C for direct cooling, and 70 to 95 degrees C for indirect cooling.

By contrast the Bukh DV10/24 Manual specifies 50 to 75 degrees C whether direct or indirect cooled.

Which agrees with Perkins as well ...

Max 60C with direct ... 65 - 93C for indirect

 

[Refueler]

Take care to distinguish between 'salt' and 'salts'.
Common salt, sodium chloride, the stuff that is in sea water. More soluble at higher temperature.
Other salts include compounds of iron, aluminium or whatever, more likely to be formed at higher temperatures.
There is also calcium and other stuff about.
Your engine will corrode more at higher temperatures, the scale produced may then trap salt.
There is calcium in sea water, enough for your engine to scale up like a kettle if you run it hot enough for long enough.
I guess that varies a lot from the Solent Brown to the Gin Clear Med or whatever.

It's not so simple as rinsing out the sodium chloride after use. But that helps. Outboards which don't get rinsed for instance end up full of corrosion. Then full of holes.

It's surprising that raw water cooling works at all really, but like Victorian piers, cast iron can be fairly long lived in seawater.

Thanks for Chemistry lesson - but it does not change the advice from engine manufacturers that above 60C on direct cooling - saltS will start to deposit ... and that in Indirect cooling of course you don't have that problem .....

As an ex Lab owner - I can say that comment "Common salt, sodium chloride, the stuff that is in sea water " is a bit sparse on reality !! Seawater in fact is a combine of many different salts derived from so many factors, such as the rivers passing over rocxks / beds / strata .... including even what is collected by rain as it falls through the air !!

 

[lw395]

Thanks for Chemistry lesson - but it does not change the advice from engine manufacturers that above 60C on direct cooling - saltS will start to deposit ... and that in Indirect cooling of course you don't have that problem .....

As an ex Lab owner - I can say that comment "Common salt, sodium chloride, the stuff that is in sea water " is a bit sparse on reality !! Seawater in fact is a combine of many different salts derived from so many factors, such as the rivers passing over rocxks / beds / strata .... including even what is collected by rain as it falls through the air !!

My remark was a reaction to other posters.
Completely agree that indirect cooling is a better 'solution' (see what I did there?) avoiding the problem, but direct cooled engines have given good service to many people over the years. I had a 1GM which worked fine for me.
But now I've grown used to boats with calorifiers and actual hot water for washing up, I wouldn't go back. I came close to buying another 1GM powered boat and even started looking at indirect cooling conversions. But recalling what the 1GM was like (noise and vibration, hard to say where pne stops and the other takes over...), something with a more reasonable number of cylinders might be a better bet. That was an aftermarket DIY conversion of an outboard boat to be fair.

 

[oldmanofthehills]

Bukh suggests that indirect cooling is only required if the engine does more than about 500 hours per annum (but doesn't state the rationale for that recommendation).

The Bukh DV36 Manual specifies the working temperature as 50 to 70 degrees C for direct cooling, and 70 to 95 degrees C for indirect cooling.

By contrast the Bukh DV10/24 Manual specifies 50 to 75 degrees C whether direct or indirect cooled.

Marine Enterprises said about 82 degrees for my indirect cooled DV24. Slightly alarmed me until I spoke to them as temp guage was unchanged and all of sudden new engine was touching the mid green to bordering red

 

[jamie N]

Bukh suggests that indirect cooling is only required if the engine does more than about 500 hours per annum (but doesn't state the rationale for that recommendation).

Like you, I'd like to discuss that with them for clarity?