Fresh Water/Raw Water Cooling ?

[NIC SURRY]

I've allways wondered why most V8 engines for marine application allways seem to be Cast Iron Blocks and heads. With Raw water cooling suffering with all the problems that occur with salt water and freezing blocks.With the alloy block alloy head engines being so much lighter why are these not being used as surely with a fresh water sealed system(antifreeze-corrosion inibitor) its the way forward or are there major problems with fresh water cooling,to the novice the only additional weight seems to be the heat exchanger and a few extra hoses and surely in the event of failiure of the raw water pump a sealed system has a better chance of survival ie; it would boil over as per a car hopefully spotted by the temp gauge or warning buzzer?,can exhaust manifold/headers be encompassed with the fresh water cooling or are these still raw water cooled if fresh water would this allow the use of alloy for this again saving weight.I'm sure there's some very knowledgable people on here that can give the pro and cons of each system to a novice. As most manufacturers seem to be producing Alloy units it could open the door to a lot more automotive units being used in marine instalations as Illmore.I'm just being enquisitive-Thanks Nic

[Tony Davis]

Most of the Mercruiser raw water cooled motors are available as fresh water, and the latest big uns are fresh as standard.

[Matt]

Historically, it wasn't really necessary, an iron motor lasted long enough, especially in fresh water. But basically it made em cheaper. Downside is less than optimal running temp, bigger bore clearances and ring end gaps, plus the accumulation of crap in the block over time.

As TD says, all the big stuff is closed cooled now. Ya still have to winterise them though.
With Ali, it's not just the internals, but external bits too that fuzz up. I've just ordered some heads and have had em anodised, but I bet it'll be a constant battle.
Running a hotter thermostat is better for emissions, better for the motor if built for it, not really any downside i can think of other than cost and more plumbing.

The arrow motor will be closed cooled.

[Alacrity]

Never really understood it myself either, but, as others have said, the cost factor came into play I think. Also a lot of motors originate in the USA where a high percentage of their boating (certainly leisure wise) is on fresh water.

Other than cost & weight, indirect cooling is win win as far as I am concerned. Normally the ex manifold will run in raw water still though, although I have seen them hooked up to the fresh water system, so long as the heat exchanger is big enough to cope I can only see advantages here as well.

I am not, however up to speed on recent developments so others here may be better informed & may be be to advise you better than I..