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scraggs

Engine Cooling

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Just seeing a post on facebook about fitting a new engine in a boat and it got me thinking about this again.

Is there any particular reason boat engines don't run a conventional cooling system ?
I assume it's to do with overheating in a confined space and maybe a cooler exhaust side of things ?, but we run both big and small engines in enclosed spaces at work and have never yet had an issue with overheating.

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Where do your engines get their cooling air from? It's usually ducted in from outside via fans if it's a truly enclosed space. On a boat, with a limited amount of air intake into the engine area (usually under a floor somewhere), you'd have to have large vents in the hull, and probably a cooling fan in front of a radiator. There's a limited amount of room for all that on a boat. You certainly couldn't find room for a fan and radiator on mine!

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I would guess that an unlimited supply of free cooling water just outside has something to do with it. water cooling is more efficient than air cooling, so can be done in a more compact space.

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And water cooling produces a lot less noise compared to air/water cooling. :)

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Land based gensets have radiator cooling but the radiators are huge with great big fans on them, not much good on a Broads boat.

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Hi Scraggs It is noise it would make. and the size of the air intakes and exhaust air exits would have to be,  these would have to be in the hull which would unsightly noisy and if boat tipped let water in water cooled 3/4 inch hole with valve to let water in a then squirt/direct into exhaust system cooling the exhaust pipe and gasses  which exit the rear/side low down to direct the fumes away from persons. your air cooled engine will have the exhaust going vertically through roof along with cooling air difficult to do on a holiday boat. John 

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I remember raising this a few years ago, but people thought I was initially referring to 'air cooled engines' (like a VW Beetle).

I thought the main issue would be larger physical holes in hulls and that is not something things that generally like to float ought to have, but my idea was you have a conventional engine of choice, far easier to source and cheaper than a marinised version. Then you simply mount the radiator in a separate enclosed externally, could be 'hidden' within a GRP louvred box that contained the fans. I am sure this would work perfectly well, since under most conditions marine engines operate at pretty low RPM's.

The only bonus would be a possible cost saving on the new engine, anything else though will be hassle and those fans will cause a racket when running too. All in all therefore the best idea I think is stick to marinised raw water cooled systems.

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I marinised a pair of car engines for my old boat but went for the normal route of closed circuit coolant and heat exchanger, I originally made up my own water cooled manifolds/heatexchanger/header units but the welds kept cracking so in the end went for bowman header/exchanger and separate cooled manifolds, they run smooth and saved me a fortune (about £2.5K total for 2 engines sourced, overhauled, marinised, fitted, with new iroko bearers glassed in. Ok it didn't include the silly number of my hours put into it and a few favours were used.

But with all that cold water under the boat why would you use air for cooling?

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Marinising a engine is mostly enclosing the exhaust manifold in a water jacket otherwise it would get red hot and cooling the sump oil, this  is not needed  on vehicles as there is a flow of air around the sump and exhaust system to keep them cool, the sump oil also helps to cool the interior of the engine, And like any low production item like marinising/altering a engine adds to costs. John

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