engine question from a newby..

[craigbalsillie]

Marine diesels?

I read a post about marininsing a diesel and the post mentioned upgrading the pump to handle saltwater and also mentioned a header tank for fresh water...

I though to start with that the salt water was for the cooling system but having slept on it, that would be silly..
so , if i am right and the fresh water is the cooling system...
what's the salt water for, apart form sailing in...

cheers,,,


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[duncan]

cooling the fresh water via a heat exchanger - in some setups but not all. Can also be cooled direct by seawater but that has lots of problems and only simplicity going for it.

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[craigbalsillie]

Of course... there is no radiator is there...
doh!

thanks for that..

so the heat exchanger.. how does that work then, similar to a radiator I guess..
a water jacket type effect with the "hot" fresh water inside immersed in a "cold" sea water...?


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[duncan]

Re: yes....(nm)

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[chippie]

Another not so common cooling method is keel cooling where the engine is cooled by freshwater that is circulated through pipes alongside the keel (think of these as the radiator in a car). There is usually a separate saltwater input that cools the exhaust . The manifold would have to be lagged as there is no waterjacket around it.

Cheers

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[snowleopard]

also...

the cold salt water, having cooled the fresh water in the block, is injected into the exhaust to prevent the rubber pipe melting.

a fresh water cooled engine has two water pumps, one for fresh and one for salt.

other differences: a fresh water cooled engine runs about 10 deg C hotter as it is under pressure which prevents the water from boiling. they will also either not have zinc anodes in the cylinder block or if they do they won't need changing so often. raw water cooled engines are difficult to use for domestic water heating through a calorifier.

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[tcm]

Re: anode/engine question

ooh a chance here for me to ask a supplementary. These MAN v12 diesel engines with ( i think) freshwater secondary cooling i have have no anodes innem. But the caterpillar 426 hp ones did, and they had a separate expenaion filing tank for the coolant, whereas these MAN diesels don't. So why's that then? Any ideas?

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[craigbalsillie]

Re: anode/engine question

I didn't realise you sailde a small frigate TCM..

A MAN V12,,, bugger me that's a bit of a beast isn't it..

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[tr7v8]

Re: anode/engine question

It depends on design origins and layout. If designed from scratch as a marine engine then generally their won't be a mix of metals in the cooling system that demand an anode. However if either by cock up or design this does occur then the manufacturers have no option but to add anodes. I do remember someone posting that Volvo thought it a waste of time.
As regards the reservoir thats just design, my Volvos run a header tank integral with the fresh cooling loop, but it could have just been an expansion tank and filled thru' that. Sensible thing I've seen in some boat reviews is mount the headers somewhere where they ca be got at like under a bunk. then coolant checks without lifting floors!

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Draco 2500

 

[colvic]

Re: anode/engine question

You want to hear a pair of them inside a dep lock on the French canals...very impressive.


Phil

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