Why have a thermostat on a raw water cooled engine?

[jamie N]

Just mulling the point, the engine that I've just rebuilt had an enormous salt build up inside the barrel, with about '75%' of the volume taken up with these salt crystals. As a part of the rebuild, I was renewing the exhaust elbow anyway, which is where the thermostat is sited, with a stainless unit and no thermostat, and just having the cooling water cool and then out of the exhaust. The most basic system.
I searched around for info on this and it appeared to show that above 60°C-70°C the salts will attach themselves to the internals of the barrel, gradually building up and blocking the cooling water. This happens when the thermostat becomes 'a little' bit blocked and on shutdown of a hot engine.
This raises the question in the title? I understand it on an engine with a heat exchanger, and I understand that the engine temp is desirable at about 75°C-85°C but it does seem to be a bit daft on a raw water engine, even with good anodes for corrosion.

 

[pvb]

Engines need to reach a working temperature in order to achieve a reasonable level of efficiency. If the engine is too cold, its thermal efficiency will be poor and it will produce less power. It may also suffer higher levels of wear. The idea of the thermostat is to allow the engine to reach a decent temperature. Salt can start to crystallise inside the engine at temperatures above about 70°C. Many raw water cooled engines will have a thermostat which starts to open at around 60°C and will be fully open at around 70°C.

If you dispense with the thermostat, your engine won't reach optimum operating conditions and you may have reduced power, increased fuel consumption and increased wear as a result.

Anodes do nothing to prevent salt crystallisation.

 

[PCUK]

52 degrees is the recommended temp' for raw water engines.

 

[pvb]

52 degrees is the recommended temp' for raw water engines.

It's rather dependent on the manufacturer's specifications. For older Volvo Penta engines, 60°C is the typical opening temperature for the thermostat. Yanmar specify a lower opening temperature (only 42°C on GM engines).

 

[vyv_cox]

The thermostat on several raw water cooled engines, Bukh and Yanmar to name two, have a dual action. As the engine warms the thermostat opens and simultaneously closes the bypass, directing cool water into the engine. Removing the thermostat will make the engine run hotter, as most water will take the path of least resistance through the bypass.

 

[PCUK]

It's rather dependent on the manufacturer's specifications. For older Volvo Penta engines, 60°C is the typical opening temperature for the thermostat. Yanmar specify a lower opening temperature (only 42°C on GM engines).

52 degrees is the well established generic average But different manufacturers will have their own ideas. I'm amazed that raw water cooling is still used anywhere as it has no advantage other than initial price Which only involves additional costs in the future due to high wear and short life.

 

[jamie N]

52 degrees is the well established generic average But different manufacturers will have their own ideas. I'm amazed that raw water cooling is still used anywhere as it has no advantage other than initial price Which only involves additional costs in the future due to high wear and short life.

That's really what I was working towards; it's just a slightly cheaper off the shelf system. My own engine is over 40 years old, so it's excusable I guess, and is now 'converted' to freshwater cooling.
As an analogy, it's a bit like 'earlier' motorcycles being air-cooled, and now having so many liquid cooled examples. Efficiency overtaking simplicity?
On a previously raw water cooled engine, it tended to run at around 30°C, albeit I'd no idea of the oil temperature.

 

[pvb]

52 degrees is the well established generic average But different manufacturers will have their own ideas. I'm amazed that raw water cooling is still used anywhere as it has no advantage other than initial price Which only involves additional costs in the future due to high wear and short life.

Most engine manufacturers stopped offering raw water cooled engines some years ago. About the only one still on sale that I can think of is the baby 10hp Yanmar.

 

[jamie N]

Cheers, I reckon that if one is assiduous about flushing and maintenance, it's got a place, but (like mine) without the flushing is potentially vulnerable to salt build up and over heating.
Interesting about the Yanmar; I was offered one at the same time!

 

[Catalina36]

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.

 

[pvb]

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.

The crystallisation occurs when the temperature is high, not after the engine has been switched off and cooled down.

 

[Catalina36]

The crystallisation occurs when the temperature is high, not after the engine has been switched off and cooled down.

And the flushing with hot fresh water while it's still soft after each run would hopefully help remove it before it became a big problem. That's precisely why people do it to outboard motors.

 

[pvb]

And the flushing with hot fresh water while it's still soft after each run would hopefully help remove it before it became a big problem. That's precisely why people do it to outboard motors.

Maybe, but most of these raw water cooled engines are already around 30 years old, so I don't know that the effort to extend their life is worthwhile, as parts shortages will most likely affect their lifespan.

 

[Poignard]

I took the liner out of my raw water cooled BUKH DV10 not long ago and I was surprised how little corrosion there was inside the block. The engine was installed in 1982.

 

[jamie N]

And the flushing with hot fresh water while it's still soft after each run would hopefully help remove it before it became a big problem. That's precisely why people do it to outboard motors.

Why specifically "hot" water, wouldn't that exacerbate the problem of crystallisation, which 'seems' to happen once cooling water has ceased to circulate?
Unfortunately, I've been googling this today, and have got bits and pieces of 'slight' information, clues really rather than facts born from the experiences that are being shared here: it does interest me!

 

[jamie N]

Maybe, but most of these raw water cooled engines are already around 30 years old, so I don't know that the effort to extend their life is worthwhile, as parts shortages will most likely affect their lifespan.

This interests me greatly. On my engine, I bought the only remaining (apparently) head gasket left in the UK! Rings are still available, so I did buy and fit a set of new rings. The injector is an item which is 'adaptably replacable' as there're so many that are similar. If the water pump goes, I'd be able to adapt a standard Jabsco or whatever. If however we've an oiling disaster which required new big ends or a new crank, the engine would be 'beyond economical repair', as I believe it's called. Out of ignorance, and having the ability to do rings, but not crankshaft stuff, wouldn't that make most engines in the 10hp area 'almost' disposable given a major problem?

 

[NormanS]

My old 6 cylinder Gardner 6L3 , (brand new in 1955) was originally raw water cooled, with the temperature controlled by using a manual bypass valve. The engine instructions recommended maintaining a temperature which, "the hand can momentarily bear"!
I would find that if bashing into bad weather, the engine had to do more " work", and so the valve would have to be adjusted.
I installed a heat exchanger, and an extra pump, to convert it to fresh water cooling, which was very successful.

 

[Refueler]

Perkins as example actually mention this matter directly and advise to run a raw water cooled engine at lower temperature to avoid salts etc being deposited in the waterways - eventually causing overheating and failure.

They specify 60C as the maximum for raw water cooled. Temperature is controlled by varying the water flow by using a manual valve .....
Later engines had a thermostat fitted to maintain this but necessitates a bypass to open when thermostat closes. The thermostat is a 60C unit.

Heat Exchanger systems (indirect) is over 65C .... and of course I would always put enough Antifreeze in - not for the cold - but to have the 'cleaning / anti-corrosion' benefit ... OK - I live in a very cold winter location and a close system would be better for me to save the flooding engine with AF before laying up ..

 

[Refueler]

My old 6 cylinder Gardner 6L3 , (brand new in 1955) was originally raw water cooled, with the temperature controlled by using a manual bypass valve. The engine instructions recommended maintaining a temperature which, "the hand can momentarily bear"!
I would find that if bashing into bad weather, the engine had to do more " work", and so the valve would have to be adjusted.
I installed a heat exchanger, and an extra pump, to convert it to fresh water cooling, which was very successful.

Me ? I'm supposed to regulate water flow - but TBH - I don't ... I have it full open and I know my engine is running cool - BUT I have still same clear waterways .. no failed exhaust parts ... engine runs sweet ..... and its been in my hands for 20yrs or so ... it was old when I got it ....

 

[VicS]

Engines need to reach a working temperature in order to achieve a reasonable level of efficiency. If the engine is too cold, its thermal efficiency will be poor and it will produce less power. It may also suffer higher levels of wear. The idea of the thermostat is to allow the engine to reach a decent temperature. Salt can start to crystallise inside the engine at temperatures above about 70°C. Many raw water cooled engines will have a thermostat which starts to open at around 60°C and will be fully open at around 70°C.

If you dispense with the thermostat, your engine won't reach optimum operating conditions and you may have reduced power, increased fuel consumption and increased wear as a result.

Anodes do nothing to prevent salt crystallisation.

You speak knowledgeably about this but why does this crystallisation occur when the temperature rises above70C ?
The available data show that the solubility of sodium chloride increases steadily with increasing temperature from just over 36g / 100cm³ at 0C to nearly 39 g/100 cm³ at 100C
and the concentration of sodium chloride in seawater is only about 1/10th of these figures anyway.