Convert Engines To Closed Cooling System

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Phil'n Nauti

Member
Mar 28, 2009
35
Cape Coral, FL
Boat Info
320 Sundancer
Engines
Twin 350 MAG Mercrusier V drives
I purchased a home in Cape Coral, FL and I am contemplating converting my 320 to a closed cooled system for when I move it down to Florida. In getting quotes I had a marina service person advise me that I have to change the ECM's on both engines to convert them "otherwise the engines will not run right"? From what I understand the ECM's are the brain of a fuel-injection system. It controls the fuel and airflow as well as the engine timing and spark curve. Why would the ECM's need to be changed to convert to a closed cooling system? Or was he trying to jack the cost of converting the engines? Can anyone provide me guidance on this, so I am not wasting hard earned money on something that does not have to be replaced. I thank all of you for your input and guidance on this matter.
 
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.
 
trit21 said:
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.
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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.
 
You will also have to change both computers or get them reprogramed. Closed cooling uses different computer just check merc parts on line.
 
trit21 said:
I didn't realize there was a full system available, learn something new all the time I guess. Thanks Westie.
Click to expand...

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.
 
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
 
speakrdude said:
"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
Click to expand...

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.
 
speakrdude said:
"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
Click to expand...

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.

On my current boat I have a factory installed half system and I have been seriously considering upgrading to a full system.
 
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.
 
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mwph said:
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.
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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.
 
Westie said:
The raw water has to go somewhere and the exhaust gases have to be cooled before going to the y pipe.
Click to expand...

This goes the point I was trying to make.

I will leave this subject alone now and I stand by my original observations that there is no such thing as a full fresh water cooled system. You can cool the engine itself or the engine and the manifolds with fresh water, but you still need raw water to cool the remainder of the exhaust system.

I know that no one here was trying to debate otherwise. I guess the words half & full just got under my skin a little. As long as the word full refers to only 2/3 of the cooling system and that you'll need another separate system to cool the other 1/3 its all good.
 
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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?
 
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