Fresh water engine cooling

[John_Walker]

I am thinking of replacing my 20 year old Volvo 2002 with a Yanmar 2GM20. The only reason for choosing this engine is that it is the only one I can find that has a starting handle and I hate the idea of relying on batteries and starter motors. One problem is that the engine is only available with a starting handle if it is the raw water cooled version. I assume the idea of fresh water cooling is to reduce internal corrosion, but does it matter? The old Volvo is raw water cooled and has lasted 20 years. Does anyone have any thoughts on the matter?

John Walker

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[Avocet]

I have a raw water cooled engine and, like yours it's 20 years old and seems OK. I change the sacrificial anodes every year. That said, I was given a similar engine for spares because the cast iron cylinder head had corroded right through the water gallery and into the exhaust port. This meant the head was completely scrap. If ever I replace this engine (perhaps I should say "when") I will want one with indirect cooling if at all possible. I'd much rather replace a heat exchanger than a cylinder head! That said, mine too can be started with a handle (at least I could when I first got it!) and although I've never needed to, I know what you mean about depending on starter motor / battery etc. Ask the dealer what the differences are and maybe you'll find it's just a relatively simple change to add the heat exchanger.

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[sailorman]

i just wonder if u have a car with a stsrting handle, only a thought.

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[paulrossall]

I have a Yanmar 2GM20 and I have a starting handle and have used it.
My car is a Volvo 940Auto which does not have a starting handle and can not be bump started. I do not carry flares, VHF radio and emergency ariel, liferaft, Avon inflateable, outboard engine, 2 anchors, emergency rations or an axe in my car!
I do not understand how safety considerations on a boat have anything to do with motor cars.

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[sailorman]

take your point.
it was slightly "tonge-in-cheak"
i have mooring 202 at Ramsholt for the past 30 years
c u some time

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[StugeronSteve]

My 2020 Volvo relies has no starting handle and the thought of a flat battery is not a pleasant one. My Mondeo has no starting handle but it's dead easy to get someone alongside to jump start it if needed.

Steve.

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[pete]

I have a 1GM 10 and have converted it to fresh water cooling after having the head corrode through above the exhaust port like one of the other posts and have a starting handle, but have been unable to swing it over compression ( MANY HAVE TRIED BUT ALL HAVE FAILED ) at least it starts at the touch of the key but I know what you mean.

Pete

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[vyv_cox]

Have you seen the correspondence a few months ago on spring-powered starter motors? In emergency these might solve your quandary.

Maybe another answer might be to invest in your battery management? In 20 years of boat ownership I have never had an engine starting problem, simply by ensuring that my starter battery is never used for anything else and is always fully charged. This is not done by any fancy electronics, simply by the discipline of changing over switches as required.

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[dickh]

There is a a company called MARTEC who do fresh water conversion kits for raw water cooled engines which have an electric pump for water circulation. May not be perfect due to your aversion to electrical kit.
I think you should get a fresh water cooled engine and live with the fact that you cannot start it if the battery is flat. Invest in a decent dedicated starter battery, with seperate domestic batteries which you could use in an emergency by a changeover switch. If you are that worried by battery failure, change the battery every 3/4 years.
With fresh water cooling you will get extended engine life because the engine will be operating at a higher temperature and hot water if you fit a calorifer.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[saturn]

decompress the engine with the lever, spin the engine then put the lever back to normal,this also works if you have a low battery.

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[theia]

i have a yanmar 2gm 20 which is the raw water cooled version, to which i fitted a 'martec' fresh water cooling system as previously mentioned. simple to fit and you can always change it back again if required. also gives you the option of hot water for free if you fit a calorifier at the same time. got everything from asap supplies. last time i checked they were doing some good deals on calorifiers.

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[timevans2000]

I have a 3 cylinder Yanmar engine installed in 1981. It cannot be hand started. It is raw water cooled. Due to its age, I am taking it out in the winter for a strip down and repaint. There is plenty of corrosion on the external oil pipes so a preventative rebuild seems prudent. It does not burn oil and has needed to oil adding between oil changes. Tho old oil was very clean after 100 hours use.

I talked to the Yanmar main dealer about retro fitting a fresh water cooloing system whilst I had the engine out. His advise was not to bother. Yanmars appear to have little problems with raw water cooling according to him. Anybody with any differnt experience?

I am not sure about fresh water cooling running hotter or why you think a hotter engine will last longer. My raw water engine has a water temp stat, so one would assume that it is operating as it was designed. It certainlt runs very well at 22 years old.

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[dickh]

Raw water engines have thermostats set to approx 60ºC, any higher and the waterways clog up very quickly and corrode faster(Hot sea water is VERY corrosive).
Fresh water cooled engines have thermostats which are in the region of 80 - 90ºC, just as hot as car or industrial engines so they run much more efficiently. The other advantage is that with fresh water cooled engines there is NO internal corrosion of the engine waterways as it is filled with a 'coolant/antifreeze' mixture just like your car engine. The sea water only cools the 'coolant/antifreeze' mixture through the heat exchanger. A much more efficient system which promotes longer engine life. It is also easier to plumb in a calorifier using the fresh water side, with benefit that the water will be hotter.


<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[vyv_cox]

The only case that I can report is a Sunsail boat in Turkey. This was a flotilla lead boat of which my son was engineer. It had no engine hour meter but had served in this duty for years, motoring everywhere something like 8 or 9 months of the year, Yanmar 30 GM raw water cooled. He thought it might have done well over 10,000 hours and was utterly reliable, used no oil and did not suffer salting up problems.

Their Volvo fresh water cooled engines were a constant source of trouble, mainly due to the plug-in piping. He converted them all back to raw water cooled, making them far less irksome.

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[timevans2000]

Not being an expert on corrosion, I am surprised that a 25 degree difference in temperature can make such as a difference. Why is slightly hotter water more corrosive and why does it clog up faster?

I appreciate that raw water running through the block is not ideal due to the potential for corrosion and build up of deposits, but there are a lot of engines out there that have been doing this for the last 20 years or so without problem. There are some advantages to.

only one pump to go wrong. No narrow water way tubes to block in the heat exchanger. less pipe work and pipe clips to maintain. less belts, etc.

I was advise not to fit one by a Yanmar dealer on the basis of little advantage and lots of cost!

I dont need hot water from my engine so this bit is not an issue. Mine is generated seperately.

I would be interested to know why the difference in stat opening temperatures though and why corrosion is worse in hotter water

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[frilaens]

The nice graph from distillation shown below is difficult to interpret but they suffer from the same problems; corrosion and scaling. They choose to operate below 70 degrees C.

<A target="_blank" HREF=http://www.ide-tech.com/code/aqua.html>http://www.ide-tech.com/code/aqua.html</A>

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[vyv_cox]

In answer to your questions there are two issues:

Corrosion is a chemical reaction. It is very well established that the rate of all chemical reactions doubles for every 10 degree C rise in temperature.

The problem with raw water cooled engines is more that the salts tend to be deposited at higher temperatures. Various engines have specific problems, for example the injection quill on Bukh engines. NaCl may redissolve but there are several nearly insoluble components of seawater and these form hard scales. Most raw water cooled engines operate at somewhere around 60 C to overcome this.

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[dickh]

I think Viv Cox's answer gives a good answer to your higher temperature query and that is how I understand the situation. However, Yanmar is one of very few purpose designed marine engines(like SAAB) which offer raw water cooling as an option, so presumably they have taken corrosion into account and they have thicker material in all the vulnerable places.
Most modern marine engines are based on auto or industrial liquid cooled engines that have been designed for light weight and speed and therefore have been designed with the minimum, and a mixture, of different metals. These obviously have to be liquid cooled to reduce the internal corrosion and galvanic action between dissimilar metals.
I accept that a raw water cooled engine has fewer bits to go wrong/block up but I personally prefer the fresh water cooled version as all that corrosion would forever be nagging at the back of my mind.
At the end of the day, it's your choice, and if you are happy with raw water cooling then thats fine.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[bob26]

ever tried bump-starting a boat?

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