How to convert a V8 Merc to a heat Xchgr?

Mr. Fisherman · 06-12-2002, 08:45 PM

Any of you Salty Dogs ever convert a V8 Mercruiser to fresh water cooling (heat exchanger)?

What is entailed and about how much should it cost if I do it myself?

Thanks in advance...

Mr. F.

Small Fry · 06-12-2002, 09:03 PM

Did you buy a new boat? :whazzup:

06-12-2002, 10:01 PM

It's a minor plumbing job. :smile:

Mr. Fisherman · 06-12-2002, 10:16 PM

Deal Pending. :grin:

shakerfish · 06-13-2002, 12:00 AM

Well now this is just my view now don't get mad please! I have a fresh water system on my boat and it has been the biggest pain in the butt! It seem to leak only when it's in the water and from where? who really knows! I havehad it in the shop 4 or 5 times they say its good to go and after about a hour or so there goes the temp gauge! and the radiator is empty! But my biggest let down was I was told by my machanic that i still have too winterize the water system each year and flush out the outdrive each time it's in salt! So I say don,t change a thing just be sure to flush and winterize as needed and you will have no problems! :smile: ...shakerfish!...

Threemuch · 06-13-2002, 05:05 AM

I concur with shakerfish. I have many salty friends who don't have fresh water cooling and have run their boats for years without issue. I have yet to know someone who had a cooling system failure due to saltwater corrosion.

KB

Orca · 06-13-2002, 09:01 AM

Hi Ray,

I have closed cooling on mine and have no problems. It was on the boat when I got it, and I am happy with it. If I recall correctly, to put a system on an engine would run about $500 - $1000 (depending on whether you put antifreeze on the manifolds (full system), or only on the block (1/2 system)) from what I have seen in the catalogs and other posts. But, check the links below to make sure I am not confused.

I have seen other posts elsewhere and attempted to decypher the whole issue. I think the bottom line is: If you put your boat in the water for the day (or 2) then pull it and flush, you should not have a problem with corrosion. If you stick your boat in the water and moor for the whole summer, then you will have a problem with corrosion.

Winterizing is slightly easier with closed cooling. I only have to let the raw water out of my heat exchanger. I have antifreeze on my manifolds, so I don't have to drain them or the block. Still have to fluch and drain outdrive though.

Do some searches here, and you will find a lot more info on systems and prices -

www.boatered.com

http://pub12.ezboard.com/bbocweb (www.boc-web.org forums)

Orca - Previously Mystic Sea

Mr. Fisherman · 06-13-2002, 11:58 PM

Thanks guys,

Hopefully I'm gonna have to make a decision soon....

Ray

Pilar · 06-14-2002, 06:33 PM

Been there .. done that.

I upgraded to the closed loop cooling during the extended refit of 'Pilar' in 1998. The Mercruiser 140 is a 4 banger inline and has the 'block only' option available. The manifold log and exhaust neck are on raw water and will eventually rot out. In the v8 systems you can do either option.

Shakerfish, I hate to tell you this but it sounds like you have a cracked block or head. Maybe the heat exchanger has a hole in it somewhere. You might get off easy with just a head gasket but hear what I said. Your symptoms coincide exactly with the problems I was having before I replaced my cracked block. It only leaks when hot because the crack expands and leaks only then. You might find it by doing a compression test. The only sure way to find it is to pressure test your water jacket and cooling system to about 10 - 12 lbs. I would do this with engine hot so the crack is expanded to full size. The test should show you the problem beyond any denial. If it leaks water will go somewhere where it shouldn't be. Into the pan, through a cracked or holed heat exchanger tube or wherever.

As for converting an existing power plant ...

'Pilar' s 140 was done during a repower. Fresh block and head. This is the best thing that ever happened to that motor. It runs cool, there are never any issues with freeze up and the erosion that caused the first engine (original) to crack is down to a 20 year rate, just like a car.

Doing it for a motor that has hours on it is a wash at best. The block would have a load of corrosion and scale built up. As you run it this normally breaks free and goes out the hub of the prop. With the closed system it will circulate and find a place to settle and clog something up. In the heat exchanger or in a narrow passage or spark plug cooling channel.

I would definitely add this relatively inexpensive item on a repower. It doubles the life of the motor. With the clean block you have no issues with scale. It will continue to look like that for years with antifreeze not saltwater for coolant. There is no scale or rust inside my 140 after 3 years.

One last thing You must insist on a pressure test with water before and after a motor is rebuilt. Boring and machining will often thin already badly eroded blocks and cause cracking. I know about this because I took an engine rebuild guys word that my original block was good to go for a rebuild. One year later I had to replace the broken block.

Just my $0.02

Mr. Fisherman · 06-18-2002, 09:48 PM

Thanks for all the replies.
It has been educational. Doesn't look like I'm gonna get to implement the original plan.

Maybe I'll buy one with FWC already installed and save my self lots of headaches.

I apopreciate everyones input :grin:

Ray

[ 06-18-2002, 10:50 PM: Message edited by: Mr. Fisherman ]

KrystalFlash · 06-18-2002, 11:46 PM

Ray, I'm sure that I could lend you some helpful advice on this. I have the FWC system on my boat......as well as diagrams of both systems...... They are in the manual... Let me know what you're up to...

M.G.