When I had my 320 I was also comtemplating changing to fresh water cooled and the dealer told me the same thing. Once I started looking into it further, I realized the exhaust manifolds would not be fresh water cooled and will still be raw salt water. So basically, it wasn't worth the money to change. My boat was equipped with a fresh water rinse down port that basically would allow me to run fresh dock water thru the engine when I docked to rinse the engine, riser and exhaust manifold after use. I choose to do that instead of spend that much money for so little gain. Not worth it IMO.

 

It depends on if you get a full or a half system. On a full system the block and manifolds are cooled by the coolant. On a half system only the block is.
I have heard the original posters concern but can not say for sure if it is true or not. A closed cooling system allows the engine to run at a more optimal temperature so there may have to be some tweaks made to the ECU to allow that.

 

I didn't realize there was a full system available, learn something new all the time I guess. Thanks Westie.

 

A full system leaves the exhaust manifold elbows cooled with raw water.
So, flushing is still a great idea..

I'm with you, just install a flush valve and leave it raw water cooled.

 

You will also have to change both computers or get them reprogramed. Closed cooling uses different computer just check merc parts on line.

 

http://bpi.ebasicpower.com/c/MER8H/Fresh+Water+Cooling+Kits+for+Mercruiser
Scroll through the listings and you will see both FULL and 1/2 listed, meaning full kit or 1/2 kit.

 

I'll offer a dissenting opinion. Before investing in cooling systems or pulling saltwater into your blocks, consider how you expect to use the boat. Florida boating is really different! I've logged many hours between a small and a mid-size cruiser in that area over the last 8 years or so (in fact, if you're on an accessible canal, I've probably cruised by your new home). Neither boat has ever been "over-nighted". The beds have been used for naps, the AC and heads have been used, but by sundown, we're always heading to a lift/rack.

I'm guessing your routine in the Great Lakes is similar to mine: after a cruise, I pull into my own slip, or a transient slip, or drop anchor and relax. The music gets turned up, cocktails get made and every moment is appreciated, because we only have so many moments. That hasn't been my experience in Florida. We don't squeeze every moment because there's an opportunity to do it all again tomorrow, and the day after, the wkd after, and of course, 6 months after... So we head for the lift before sundown, and then we pull out hose and start rinsing exterior of the boat. When that's done, we're only half done. We lift the hatch, fill the salt-away reservoir, attach the hose to the flushing fitting, start each engine and run water and solution through them. While we do this, we're also covering ourselves in deet because the no-see-ums have found us. When salt damage has been mitigated as best we can, we stow the hose, close everything up and retreat into the house.

Even after all this, the engines and manifolds are rotting from the inside out. No matter how diligent any boater is, iron and salt DO NOT play well together.

I'll admit, my opinion is based partially on experience, and partially on emotion. I didn't renew my marina contract for the 280 this season because the stbd engine shows signs of significant internal corrosion. The engine block is being consumed by salt. The port engine and all manifolds have already been replaced.

IMO, it's crazy to cool the internals of an engine with saltwater. Congrats on the purchase of your new home. The boating opportunities are incredible, but if I recommend that you take a look at the predominant style of boat there, and quiz some of your new neighbors about how they use their boats. As awesome as your 320 is, it may not suit your new boating lifestyle. I'm not saying it WON'T - I'm just pointing out that there's a lot to be said for a "throw & go" style of boat that won't consume cash and valuable time with upkeep. If you decide that the 320 will continue to suit your needs, then I would really recommend you do her the favor of closed cooling.

 

Thanks guys. I was looking for (and have often searched for) a diagram of how water/coolant in a so called full system actually cooled the exhaust manifolds. The two sentences below were copied from the monitorpro link which attempts to define a "Half" and a "Full" system....

HALF = �Raw Water� which has removed heat from the engine through the heat exchanger is then injected into the exhaust manifold, from which it flows to the exhaust elbow to cool and exit through the exhaust.

FULL = �Raw Water� which has removed heat from the engine through the heat exchanger is then injected into the exhaust elbow and exits through the engine exhaust.

Maybe I'm missing something here but I just don't get it.
Thanks for all responses. As always, I only ask in order to learn.

 

The difference between the two above phrases are Exhaust manifold and Exhaust elbow. Either and all systems will use the exhaust elbow to "dump" the hot water out the exhaust and to keep the rubber exhaust parts from melting.

When you go "Full" cooled, which is the best if you can, There HAS TO BE a block-off gasket between the exhaust manifold and the exhaust elbow, (AKA riser). This gasket keeps the glycol in the engine AND exhaust manifold, and the hot water through ONLY the Exhaust Elbow.
"Full Cooled" requires an external pump, typically a belt driven or crank-mounted pump.
The Alpha stern drive pump will not support Full-Cooled on it's own, thereby, creating the need for Half-Cooled.

Even Half-Cooled is miles ahead of raw-water cooled, for many reasons. Protects the block and circ pump. Glycol keeps metal parts lubricated and rust free.
Block runs hotter as it was designed to do. Fuel burns more efficiently. No need to drain the block in the winter. Resale value is better. No sand and crude being sucked through your block.

The ONLY reason all MFGs Do Not make it mandatory to be installed, is the few $$ extra it makes the sale price.

Convinced yet?

I install both half and full kits all the time. Let me know if you have any more questions.

Jim

 

"Full Cooled" requires an external pump, typically a belt driven or crank-mounted pump.
The Alpha stern drive pump will not support Full-Cooled on it's own, thereby, creating the need for Half-Cooled.

Jim

On my previous boat I installed a full system on a 5.0 L with an alpha drive and never had any issues with it. Now I do boat in water that has colder temperatures than a lot of places so that will have helped. I did have a long conversation with a guy from monitor before I did the conversion about the alpha drive having the water flow capacity though.

 

Thanks again. The last couple of posts from Rolercoastr & Speakerdude are what I was hoping would come into this thread.

I guess my definitions of half and full are somewhat distorted. For some reason I have read more on this subject than I care to admit. I understand the concept(s) involved, I've just become almost pissed that everything I read ignores the components after the manifold itself. I can read until my eyes hurt that SOME "full" system uses the heat exchanger to cool the block, heads & manifolds, only to be disappointed again when the last sentence tells me that a separate system uses raw water to cool the rest of the exhaust system like the risers, elbows, and mufflers.

Sorry if I've hijacked the thread, or if I'm splitting hairs, or if I'm beating a dead horse.

 

The raw water has to go somewhere and the exhaust gases have to be cooled before going to the y pipe. The area most prone to rusting is the small passages at the manifold / elbow (or risers if you have them) junction. I full system blocks this off with a block of gasket so there is no longer a weak point to fail. The dry joint exhaust set up also removes this weak point.

 

A "half-system" is engine block only, manifolds and risers raw water cooled
A "full system" is engine block and exaust manifolds fresh water cooled, riser is raw water cooled

 

Risers are always raw water cooled as the raw water needs to be discharged somewhere and something is needed to cool the risers, exhaust hoses, elbows etc. Its a fairly easy system to understand once you see one in person. A 'full system' is a far superior way to cool a marine engine than to simply circulate salt water thru the engine block, manifolds and risers. I can't imagine a more corrosive fluid to cool cast iron than hot brine solution.

 

So im changing my manifolds. I currently have a "half" fresh water cooling system. If I wanted to turn that into a "full" system what would I have to do?

 

I believe the full system uses a larger diameter heat exchanger with additional hoses and fittings to connect the heat exchanger to the manifolds. The larger heat exchanger is needed to cool the manifolds in addition to the engine block. In addition you need to add the block off plates and gaskets needed to separate the manifolds from the elbows/risers (if equipped). You can find the diagrams online. Added parts cost probably about $1200 for the heat exchanger and hoses. Sell the take offs to reduce the cost.

 

Just bought two brand new heat exchangers. .. day late a dollar short i guess. Maybe next time

 

All,

Thank you for the responses it is greatly appreciated and gives me food for thought before spending money.

 

Hey folks hoping you can help advise me similar thinking on this thread. I just bought a used 2005 Sea Ray 320 with Twin 350 Mercruiser (5.7L) MAG MPI Horizons V drive engines. The port side engine just failed with milky oil and salt water in engine. I ordered 2 new engine cores and we will reuse sea water pumps, alterators and other components. I really wanted to convert the new rebuilt engines over to full fresh water cooled heated exchangers. I have been looking at after market options but am concerned at the idea that the ECM needs to be replaced also. Does anyone have advice on if ECM can be reprogrammed or needs to be replaced? Can anyone comment on aftermarket dealer vs OEM? OEM per engine is $6300 CAD$$. That is about $4000 US per side!! Yes I know I can flush with hose kit everytime but there are times when I will not have a hose around for weeks at a time. Thanks.

 

I thought the horizons were already set up w/fwc, anyway if you are going the expense of a repower ,positively go w/fwc full and use dry joint exhaust, or try and find a ss riser for the saltwater, and change your coolers (oil and power steering)

 

Never could understand the ECM difference. I converted mine to closed cooled a couple of years ago with no issue at all. Went with a Seacamp exchanger and used all Merc hoses and T-stat housing, runs at 160 same as it was with open cooling.

 

A quick review of Mercruiser's site shows the same ECM as a part being used on both raw water and closed cooling engines. If there is no operating temp difference.....not sure why somebody would have made this up.

 

Were your manifolds and risers new at the time of conversion? How old were the engines? Thanks for this info.

 

New exhaust. Rebuilt my 20 year old engine, hot tanked and steel shot.

 

I looked at Merc's site and 10 different ECM's were used on V8's with a 0W prefix which is what the OP probably has Lot of combo's there. Does he need to change it? Don't know.

 

Oh this boat has rudders and V drive FYI