Freshwater cooling. Is it worth it?

bobtooke

bobtooke

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Is it worth converting a Mercruiser Alpha/Bravo to a closed cooling system?
My boat is based on the south coast so running with direct Seawater currently.
Is the cost of a conversion worthwhile?
What are the practical pros and cons?
 
Depends if you can drystack or not. When we drystacked we flushed the engine every time, never had an issue .... risers lasted 15 years, main components all original and engine had 800 hours
 
i think there is a fresh water flushing kit you can retro fit that will enable you to flush your Mercruiser with fresh water while its afloat. That may well make a lot of difference to the life of your exahaust risers if done religiously after every use.
 
My boat is on a marina pontoon so its in the salt 24/7 that's why I was considering the effects of the corrosive stuff.

I guess a connection in the outdrive pump line for a hose would allow you to flush whilst floating, that's a stirling idea!

Generally, I was just wondering whether the to bite the bullet and go for a closed system conversion. It's about £1000 to convert but wondering if there are any pros or cons to be aware of and if it's even worth it from someone who's maybe done it?
 
bobtooke said:
Is it worth converting a Mercruiser Alpha/Bravo to a closed cooling system?
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Closed fresh water cooling is optional on some Merc engines, and standard in their top of the line ones.
That alone tells you that it's something worth having...
But I never heard of retrofitted conversions, are you sure it's feasible?
Other than that, fresh water flushing achieves 90% of the result at (I would guess) less than 5% of the cost.
That's definitely the option I would investigate first.

As an aside, you mention Alpha/Bravo, as if cooling would have anything to see with the outdrives.
To my knowledge, there isn't any difference in them - either ways, outdrives are always raw water cooled, it's only the block that is affected.
 
I take your point re: top line models. I do believe that closed cooling is recommended for seagoing boat engines from factory and at face value seems essential.
Am I sure it's feasible? Yes, there are a number of companies that do conversion kits. Its really just a shell and tube heat exchanger that uses the outdrive cooling pump to provide seawater cooling. The engine block and manifold coolant is then separated and sealed/pressurised with inhibitor and antifreeze.
To get the original parts from Merc is about £2k but there are lots of aftermarket kits for around £1k.
Perhaps I'll try freshwater flushing for a bit and see how that goes while I save the pennies ?
 
how does the closed system protect the risers? Was under the impression this is where the exhaust and water meet. Wont this still be the same as post heat exchanger raw water will still be used to cool the exhaust , presumably via the risers?
 
david_bagshaw said:
how does the closed system protect the risers? Was under the impression this is where the exhaust and water meet. Wont this still be the same as post heat exchanger raw water will still be used to cool the exhaust , presumably via the risers?
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Yes, as I understand it, the risers atop the manifolds are the only item not protected as it is raw water mixing with the exhaust. Not a lot can be done about that really. They just have to be considered as a regular replaceable component even after the closed system is fitted.
 
Yup, your understanding is correct: also on OEM closed circuit Merc engines, risers are always raw water cooled.
Which is another reason why a fresh water cooling system is worth having anyway.
By rinsing the whole system before leaving the boat unused for some time, you leave nothing but fresh water everywhere.
I mean, not only the block and risers, but also outdrive, raw water pump and heat exchanger, should you decide to retrofit a closed circuit cooling.
And also the intercooler (if any).
 
MapisM said:
Yup, your understanding is correct: also on OEM closed circuit Merc engines, risers are always raw water cooled.
Which is another reason why a fresh water cooling system is worth having anyway.
By rinsing the whole system before leaving the boat unused for some time, you leave nothing but fresh water everywhere.
I mean, not only the block and risers, but also outdrive, raw water pump and heat exchanger, should you decide to retrofit a closed circuit cooling.
And also the intercooler (if any).
Click to expand...
That's useful to consider so as to delay replacement. Regardless of fitting a closed system, the flush facility would be good.
I suppose that if I fit a freshwater flush now, when I do convert to a closed system later, its all ready to go as you suggest.
No intercoolers I'm afraid, mine is a simple old naturally aspirated murcan v8 (yeehaw!).
 
Good thread, I'm in the middle of buying a boat that'll be dry stacked, it has a mercruiser 5.0 mag 350 engine. I didn't know anything about fresh water flushing after use...... I'll be doing some research now... cheers.
 
I had a 2006 sea ray with the merc 5.0 mpi engine that was raw water cooled. It lived in the sea 365 days per year, only coming out once per year for a few days for the usual service. It was never flushed with fresh water as it was always too much hassle. I owned it from brand new for 7 years, and it was still fine when I sold it, I still see it around and running fine.

Around 2002/2003 mercruiser redesigned the exhaust risers and switched to a dry joint design that eliminated the mode of failure that was common is the older style wet joint exhaust risers that would effectively trash the engine if the issue occurred.

So on the assumption were talking about an engine with the dry joint risers, I'd say flushing with fresh is worth it if you can easily do it, but not an essential thing, and retrofitting a fresh water closed cooling system is probably less worthwhile.
 
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